Implement HEVC intra picture reconstruction

src/ImageSharp/Formats/Heif/Hevc/HevcCabacContexts.cs

@@ -111,7 +111,7 @@ internal sealed class HevcCabacContexts
     /// <summary>
     /// The number of contexts used by the independently coded intra-picture syntax.
     /// </summary>
-    private const int ContextCount = 178;
+    public const int ContextCount = 178;
 
     /// <summary>
     /// The contiguous adaptive context storage owned by the entropy substream.
@@ -304,4 +304,16 @@ internal sealed class HevcCabacContexts
     /// </summary>
     public Span<HevcCabacContext> CrossComponentPrediction =>
         this.contexts.AsSpan(CrossComponentPredictionOffset, 10);
+
+    /// <summary>
+    /// Copies every adaptive probability context to caller-owned wavefront state.
+    /// </summary>
+    /// <param name="destination">The destination containing at least <see cref="ContextCount"/> elements.</param>
+    public void CopyTo(Span<HevcCabacContext> destination) => this.contexts.CopyTo(destination);
+
+    /// <summary>
+    /// Restores every adaptive probability context from caller-owned wavefront state.
+    /// </summary>
+    /// <param name="source">The source containing at least <see cref="ContextCount"/> elements.</param>
+    public void CopyFrom(ReadOnlySpan<HevcCabacContext> source) => source[..ContextCount].CopyTo(this.contexts);
 }

src/ImageSharp/Formats/Heif/Hevc/HevcCabacDecoder.cs

@@ -33,6 +33,11 @@ internal ref struct HevcCabacDecoder
     /// </summary>
     private int bitsNeeded;
 
+    /// <summary>
+    /// The raw-bit position used while a pulse-code-modulated coding unit suspends arithmetic decoding.
+    /// </summary>
+    private int pcmBitOffset;
+
     /// <summary>
     /// Initializes a new instance of the <see cref="HevcCabacDecoder"/> struct.
     /// </summary>
@@ -50,6 +55,7 @@ internal ref struct HevcCabacDecoder
         this.range = 510;
         this.value = ((uint)data[0] << 8) | data[1];
         this.bitsNeeded = -8;
+        this.pcmBitOffset = 0;
     }
 
     /// <summary>
@@ -263,6 +269,67 @@ internal ref struct HevcCabacDecoder
         return false;
     }
 
+    /// <summary>
+    /// Decodes the terminating-bin flag that enters pulse-code-modulated sample syntax.
+    /// </summary>
+    /// <returns><see langword="true"/> when raw PCM samples follow; otherwise, <see langword="false"/>.</returns>
+    public bool ReadPcmFlag()
+    {
+        bool pcm = this.ReadTerminate();
+        if (pcm)
+        {
+            // A successful terminating bin leaves the underlying byte reader at the first byte after the CABAC
+            // alignment pattern. PCM sample bits start there and temporarily bypass the arithmetic registers.
+            this.pcmBitOffset = this.byteOffset * 8;
+        }
+
+        return pcm;
+    }
+
+    /// <summary>
+    /// Reads one unsigned pulse-code-modulated sample while arithmetic decoding is suspended.
+    /// </summary>
+    /// <param name="bitDepth">The number of most-significant-bit-first sample bits.</param>
+    /// <returns>The decoded sample value.</returns>
+    /// <exception cref="InvalidImageContentException">The entropy substream ends within the PCM sample.</exception>
+    public ushort ReadPcmSample(int bitDepth)
+    {
+        DebugGuard.MustBeBetweenOrEqualTo(bitDepth, 1, 16, nameof(bitDepth));
+        if (this.pcmBitOffset > (this.data.Length * 8) - bitDepth)
+        {
+            throw new InvalidImageContentException("The HEVC pulse-code-modulated sample data is truncated.");
+        }
+
+        uint sample = 0;
+        int bitsRemaining = bitDepth;
+        while (bitsRemaining > 0)
+        {
+            int byteIndex = this.pcmBitOffset >> 3;
+            int bitIndex = this.pcmBitOffset & 7;
+            int bitsFromByte = Math.Min(8 - bitIndex, bitsRemaining);
+            int shift = 8 - bitIndex - bitsFromByte;
+            uint mask = (uint)((1 << bitsFromByte) - 1);
+            sample = (sample << bitsFromByte) | ((uint)(this.data[byteIndex] >> shift) & mask);
+            this.pcmBitOffset += bitsFromByte;
+            bitsRemaining -= bitsFromByte;
+        }
+
+        return (ushort)sample;
+    }
+
+    /// <summary>
+    /// Restarts arithmetic decoding after a complete byte-aligned PCM coding unit.
+    /// </summary>
+    /// <exception cref="InvalidImageContentException">The following arithmetic substream is truncated.</exception>
+    public void RestartAfterPcm()
+    {
+        DebugGuard.IsTrue((this.pcmBitOffset & 7) == 0, "The complete HEVC PCM payload must end on a byte boundary.");
+        this.byteOffset = this.pcmBitOffset >> 3;
+        this.range = 510;
+        this.bitsNeeded = -8;
+        this.value = ((uint)this.ReadByte() << 8) | this.ReadByte();
+    }
+
     /// <summary>
     /// Validates the stop bit and zero padding following a terminating entropy-coded value.
     /// </summary>

src/ImageSharp/Formats/Heif/Hevc/HevcCabacSyntaxReader.cs

@@ -45,6 +45,18 @@ internal ref struct HevcCabacSyntaxReader
     /// </summary>
     public readonly int BytesConsumed => this.decoder.BytesConsumed;
 
+    /// <summary>
+    /// Copies the adaptive contexts required to initialize a later wavefront row.
+    /// </summary>
+    /// <param name="destination">The caller-owned context destination.</param>
+    public readonly void CopyContextsTo(Span<HevcCabacContext> destination) => this.contexts.CopyTo(destination);
+
+    /// <summary>
+    /// Restores adaptive contexts captured after the second coding-tree block of the preceding wavefront row.
+    /// </summary>
+    /// <param name="source">The saved wavefront contexts.</param>
+    public readonly void CopyContextsFrom(ReadOnlySpan<HevcCabacContext> source) => this.contexts.CopyFrom(source);
+
     /// <summary>
     /// Decodes the coding-unit transquant-bypass flag.
     /// </summary>
@@ -87,6 +99,24 @@ internal ref struct HevcCabacSyntaxReader
         return !this.decoder.ReadDecision(ref selectedContexts[0]);
     }
 
+    /// <summary>
+    /// Decodes whether a square intra coding unit carries raw pulse-code-modulated samples.
+    /// </summary>
+    /// <returns><see langword="true"/> when PCM sample syntax follows; otherwise, <see langword="false"/>.</returns>
+    public bool ReadPcmFlag() => this.decoder.ReadPcmFlag();
+
+    /// <summary>
+    /// Reads one pulse-code-modulated component sample.
+    /// </summary>
+    /// <param name="bitDepth">The PCM sample precision.</param>
+    /// <returns>The decoded unsigned sample.</returns>
+    public ushort ReadPcmSample(int bitDepth) => this.decoder.ReadPcmSample(bitDepth);
+
+    /// <summary>
+    /// Restarts arithmetic decoding after the complete PCM coding-unit payload.
+    /// </summary>
+    public void RestartAfterPcm() => this.decoder.RestartAfterPcm();
+
     /// <summary>
     /// Decodes whether a luma intra mode is selected from the three most-probable modes.
     /// </summary>

src/ImageSharp/Formats/Heif/Hevc/HevcCodedBlockFlags.cs

@@ -0,0 +1,53 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <summary>
+/// Contains one or two coded-block flags for a square or vertically split HEVC component transform section.
+/// </summary>
+internal readonly struct HevcCodedBlockFlags
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcCodedBlockFlags"/> struct for one square block.
+    /// </summary>
+    /// <param name="first">The square block's coded-block flag.</param>
+    public HevcCodedBlockFlags(bool first)
+    {
+        this.First = first;
+        this.Second = false;
+        this.IsSplit = false;
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcCodedBlockFlags"/> struct for two rectangular sub-blocks.
+    /// </summary>
+    /// <param name="first">The first square sub-block's coded-block flag.</param>
+    /// <param name="second">The second square sub-block's coded-block flag.</param>
+    public HevcCodedBlockFlags(bool first, bool second)
+    {
+        this.First = first;
+        this.Second = second;
+        this.IsSplit = true;
+    }
+
+    /// <summary>
+    /// Gets a value indicating whether the first or only coefficient block contains coded residual data.
+    /// </summary>
+    public bool First { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the second rectangular sub-block contains coded residual data.
+    /// </summary>
+    public bool Second { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether two square sub-block flags are present.
+    /// </summary>
+    public bool IsSplit { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether either governed coefficient block contains coded residual data.
+    /// </summary>
+    public bool Any => this.First || this.Second;
+}

src/ImageSharp/Formats/Heif/Hevc/HevcCodingTreeState.cs

@@ -30,6 +30,16 @@ internal sealed class HevcCodingTreeState : IDisposable
     /// </summary>
     private readonly Buffer2D<sbyte> quantizationParameters;
 
+    /// <summary>
+    /// The combined picture, slice, and coding-unit Cb quantization offsets at minimum-coding-block resolution.
+    /// </summary>
+    private readonly Buffer2D<sbyte> chromaBlueQuantizationOffsets;
+
+    /// <summary>
+    /// The combined picture, slice, and coding-unit Cr quantization offsets at minimum-coding-block resolution.
+    /// </summary>
+    private readonly Buffer2D<sbyte> chromaRedQuantizationOffsets;
+
     /// <summary>
     /// The packed bypass and PCM flags at minimum-coding-block resolution.
     /// </summary>
@@ -59,6 +69,14 @@ internal sealed class HevcCodingTreeState : IDisposable
             this.WidthInMinCodingBlocks,
             this.HeightInMinCodingBlocks);
 
+        this.chromaBlueQuantizationOffsets = configuration.MemoryAllocator.Allocate2D<sbyte>(
+            this.WidthInMinCodingBlocks,
+            this.HeightInMinCodingBlocks);
+
+        this.chromaRedQuantizationOffsets = configuration.MemoryAllocator.Allocate2D<sbyte>(
+            this.WidthInMinCodingBlocks,
+            this.HeightInMinCodingBlocks);
+
         this.flags = configuration.MemoryAllocator.Allocate2D<byte>(
             this.WidthInMinCodingBlocks,
             this.HeightInMinCodingBlocks);
@@ -114,6 +132,8 @@ internal sealed class HevcCodingTreeState : IDisposable
     /// <param name="log2Size">The base-two logarithm of the square coding-unit size.</param>
     /// <param name="depth">The coding-tree depth.</param>
     /// <param name="quantizationParameter">The effective luma quantization parameter.</param>
+    /// <param name="chromaBlueQuantizationOffset">The combined Cb quantization-parameter offset.</param>
+    /// <param name="chromaRedQuantizationOffset">The combined Cr quantization-parameter offset.</param>
     /// <param name="transquantBypass">A value indicating whether transform and quantization are bypassed.</param>
     /// <param name="pcm">A value indicating whether the coding unit contains pulse-code-modulated samples.</param>
     public void SetCodingUnit(
@@ -122,6 +142,8 @@ internal sealed class HevcCodingTreeState : IDisposable
         int log2Size,
         int depth,
         int quantizationParameter,
+        int chromaBlueQuantizationOffset,
+        int chromaRedQuantizationOffset,
         bool transquantBypass,
         bool pcm)
     {
@@ -138,6 +160,8 @@ internal sealed class HevcCodingTreeState : IDisposable
         {
             this.depths.DangerousGetRowSpan(row)[unitX..endX].Fill((byte)depth);
             this.quantizationParameters.DangerousGetRowSpan(row)[unitX..endX].Fill((sbyte)quantizationParameter);
+            this.chromaBlueQuantizationOffsets.DangerousGetRowSpan(row)[unitX..endX].Fill((sbyte)chromaBlueQuantizationOffset);
+            this.chromaRedQuantizationOffsets.DangerousGetRowSpan(row)[unitX..endX].Fill((sbyte)chromaRedQuantizationOffset);
             this.flags.DangerousGetRowSpan(row)[unitX..endX].Fill(packedFlags);
         }
     }
@@ -160,6 +184,18 @@ internal sealed class HevcCodingTreeState : IDisposable
     public int GetQuantizationParameter(int x, int y)
         => this.quantizationParameters.DangerousGetRowSpan(y >> this.MinCodingBlockLog2)[x >> this.MinCodingBlockLog2];
 
+    /// <summary>
+    /// Gets the combined chroma quantization-parameter offset at a luma sample coordinate.
+    /// </summary>
+    /// <param name="plane">The Cb or Cr reconstruction plane.</param>
+    /// <param name="x">The luma sample X coordinate.</param>
+    /// <param name="y">The luma sample Y coordinate.</param>
+    /// <returns>The selected picture, slice, and coding-unit offset.</returns>
+    public int GetChromaQuantizationOffset(HevcPlane plane, int x, int y)
+        => plane == HevcPlane.Cb
+            ? this.chromaBlueQuantizationOffsets.DangerousGetRowSpan(y >> this.MinCodingBlockLog2)[x >> this.MinCodingBlockLog2]
+            : this.chromaRedQuantizationOffsets.DangerousGetRowSpan(y >> this.MinCodingBlockLog2)[x >> this.MinCodingBlockLog2];
+
     /// <summary>
     /// Gets a value indicating whether the coding unit at a luma sample coordinate bypasses transform and quantization.
     /// </summary>
@@ -187,6 +223,8 @@ internal sealed class HevcCodingTreeState : IDisposable
     {
         this.depths.Dispose();
         this.quantizationParameters.Dispose();
+        this.chromaBlueQuantizationOffsets.Dispose();
+        this.chromaRedQuantizationOffsets.Dispose();
         this.flags.Dispose();
     }
 

src/ImageSharp/Formats/Heif/Hevc/HevcCoefficientCodingParameters.cs

@@ -126,6 +126,7 @@ internal readonly struct HevcCoefficientCodingParameters
     /// <param name="transformSkip">Whether the transform block bypasses the inverse transform.</param>
     /// <param name="transquantBypass">Whether the coding unit bypasses inverse quantization and inverse transform.</param>
     /// <param name="residualDpcmMode">The residual differential-pulse-code-modulation mode selected for the block.</param>
+    /// <param name="useLumaSyntax">Whether a separately coded color plane uses the luma coefficient context set.</param>
     /// <returns>The coefficient entropy-coding parameters for the transform block.</returns>
     public static HevcCoefficientCodingParameters Create(
         HevcPictureParameterSet pictureParameterSet,
@@ -136,15 +137,17 @@ internal readonly struct HevcCoefficientCodingParameters
         int intraPredictionMode,
         bool transformSkip,
         bool transquantBypass,
-        HevcResidualDpcmMode residualDpcmMode)
+        HevcResidualDpcmMode residualDpcmMode,
+        bool useLumaSyntax = false)
     {
         HevcSequenceParameterSet sequenceParameterSet = pictureParameterSet.SequenceParameterSet;
-        bool isChroma = plane != HevcPlane.Y;
+        HevcPlane codingPlane = useLumaSyntax ? HevcPlane.Y : plane;
+        bool isChroma = codingPlane != HevcPlane.Y;
         bool nonTransformed = transformSkip || transquantBypass;
         HevcCoefficientScanType scanType = SelectScanType(
             width,
             height,
-            plane,
+            codingPlane,
             isIntra,
             intraPredictionMode,
             sequenceParameterSet.ChromaFormat,

src/ImageSharp/Formats/Heif/Hevc/HevcCoefficientDecoder.cs

@@ -96,6 +96,23 @@ internal sealed class HevcCoefficientDecoder : IDisposable
         8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9,
     ];
 
+    /// <summary>
+    /// Clears all persistent Rice adaptation statistics for a newly initialized entropy substream.
+    /// </summary>
+    public void ResetRiceAdaptation() => this.riceAdaptationStatistics = default;
+
+    /// <summary>
+    /// Copies the four persistent Rice adaptation statistics to caller-owned wavefront state.
+    /// </summary>
+    /// <param name="destination">The four-element destination.</param>
+    public void CopyRiceAdaptationTo(Span<int> destination) => this.riceAdaptationStatistics[..4].CopyTo(destination);
+
+    /// <summary>
+    /// Restores the four persistent Rice adaptation statistics captured for a later wavefront row.
+    /// </summary>
+    /// <param name="source">The four saved statistics.</param>
+    public void CopyRiceAdaptationFrom(ReadOnlySpan<int> source) => source[..4].CopyTo(this.riceAdaptationStatistics[..4]);
+
     /// <summary>
     /// Decodes one transform block into raster-ordered signed coefficient levels.
     /// </summary>

src/ImageSharp/Formats/Heif/Hevc/HevcDeblockingFilter.cs

@@ -0,0 +1,614 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Runtime.CompilerServices;
+using System.Runtime.Intrinsics;
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <summary>
+/// Applies the HEVC luma and chroma deblocking kernels to four-sample edge segments.
+/// </summary>
+internal static class HevcDeblockingFilter
+{
+    /// <summary>
+    /// Defines orientation-specific access to the four samples running along one deblocking edge segment.
+    /// </summary>
+    private interface IEdgeOperator
+    {
+        /// <summary>
+        /// Loads four samples at one signed distance across the edge.
+        /// </summary>
+        /// <param name="picture">The reconstructed picture.</param>
+        /// <param name="plane">The component plane.</param>
+        /// <param name="x">The first Q-side sample X coordinate.</param>
+        /// <param name="y">The first Q-side sample Y coordinate.</param>
+        /// <param name="distance">The signed sample distance across the edge.</param>
+        /// <returns>Four widened samples ordered along the edge.</returns>
+        public static abstract Vector128<int> LoadVector(HevcPictureBuffer picture, HevcPlane plane, int x, int y, int distance);
+
+        /// <summary>
+        /// Stores four samples at one signed distance across the edge.
+        /// </summary>
+        /// <param name="picture">The reconstructed picture.</param>
+        /// <param name="plane">The component plane.</param>
+        /// <param name="x">The first Q-side sample X coordinate.</param>
+        /// <param name="y">The first Q-side sample Y coordinate.</param>
+        /// <param name="distance">The signed sample distance across the edge.</param>
+        /// <param name="value">The four widened samples ordered along the edge.</param>
+        /// <param name="count">The number of low lanes to store.</param>
+        public static abstract void StoreVector(
+            HevcPictureBuffer picture,
+            HevcPlane plane,
+            int x,
+            int y,
+            int distance,
+            Vector128<int> value,
+            int count);
+
+        /// <summary>
+        /// Loads one scalar sample at a signed distance across and an offset along the edge.
+        /// </summary>
+        /// <param name="picture">The reconstructed picture.</param>
+        /// <param name="plane">The component plane.</param>
+        /// <param name="x">The first Q-side sample X coordinate.</param>
+        /// <param name="y">The first Q-side sample Y coordinate.</param>
+        /// <param name="distance">The signed sample distance across the edge.</param>
+        /// <param name="index">The sample offset along the edge.</param>
+        /// <returns>The selected sample.</returns>
+        public static abstract int LoadScalar(HevcPictureBuffer picture, HevcPlane plane, int x, int y, int distance, int index);
+
+        /// <summary>
+        /// Stores one scalar sample at a signed distance across and an offset along the edge.
+        /// </summary>
+        /// <param name="picture">The reconstructed picture.</param>
+        /// <param name="plane">The component plane.</param>
+        /// <param name="x">The first Q-side sample X coordinate.</param>
+        /// <param name="y">The first Q-side sample Y coordinate.</param>
+        /// <param name="distance">The signed sample distance across the edge.</param>
+        /// <param name="index">The sample offset along the edge.</param>
+        /// <param name="value">The filtered sample.</param>
+        public static abstract void StoreScalar(HevcPictureBuffer picture, HevcPlane plane, int x, int y, int distance, int index, int value);
+    }
+
+    /// <summary>
+    /// Filters four rows crossing one vertical luma boundary.
+    /// </summary>
+    /// <param name="picture">The reconstructed picture.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The first Q-side sample X coordinate.</param>
+    /// <param name="y">The top sample Y coordinate.</param>
+    /// <param name="beta">The scaled discontinuity threshold.</param>
+    /// <param name="tc">The scaled clipping threshold.</param>
+    /// <param name="partPNoFilter">Whether the P-side block retains its original samples.</param>
+    /// <param name="partQNoFilter">Whether the Q-side block retains its original samples.</param>
+    /// <param name="bitDepth">The component sample precision.</param>
+    public static void FilterVerticalLuma(
+        HevcPictureBuffer picture,
+        HevcPlane plane,
+        int x,
+        int y,
+        int beta,
+        int tc,
+        bool partPNoFilter,
+        bool partQNoFilter,
+        int bitDepth)
+        => FilterLuma<VerticalEdgeOperator>(picture, plane, x, y, beta, tc, partPNoFilter, partQNoFilter, bitDepth);
+
+    /// <summary>
+    /// Filters four columns crossing one horizontal luma boundary.
+    /// </summary>
+    /// <param name="picture">The reconstructed picture.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The left sample X coordinate.</param>
+    /// <param name="y">The first Q-side sample Y coordinate.</param>
+    /// <param name="beta">The scaled discontinuity threshold.</param>
+    /// <param name="tc">The scaled clipping threshold.</param>
+    /// <param name="partPNoFilter">Whether the P-side block retains its original samples.</param>
+    /// <param name="partQNoFilter">Whether the Q-side block retains its original samples.</param>
+    /// <param name="bitDepth">The component sample precision.</param>
+    public static void FilterHorizontalLuma(
+        HevcPictureBuffer picture,
+        HevcPlane plane,
+        int x,
+        int y,
+        int beta,
+        int tc,
+        bool partPNoFilter,
+        bool partQNoFilter,
+        int bitDepth)
+        => FilterLuma<HorizontalEdgeOperator>(picture, plane, x, y, beta, tc, partPNoFilter, partQNoFilter, bitDepth);
+
+    /// <summary>
+    /// Filters four rows crossing one vertical chroma boundary.
+    /// </summary>
+    /// <param name="picture">The reconstructed picture.</param>
+    /// <param name="plane">The Cb or Cr component plane.</param>
+    /// <param name="x">The first Q-side sample X coordinate.</param>
+    /// <param name="y">The top sample Y coordinate.</param>
+    /// <param name="tc">The scaled clipping threshold.</param>
+    /// <param name="partPNoFilter">Whether the P-side block retains its original samples.</param>
+    /// <param name="partQNoFilter">Whether the Q-side block retains its original samples.</param>
+    /// <param name="bitDepth">The component sample precision.</param>
+    /// <param name="count">The number of samples in the edge segment.</param>
+    public static void FilterVerticalChroma(
+        HevcPictureBuffer picture,
+        HevcPlane plane,
+        int x,
+        int y,
+        int tc,
+        bool partPNoFilter,
+        bool partQNoFilter,
+        int bitDepth,
+        int count)
+        => FilterChroma<VerticalEdgeOperator>(picture, plane, x, y, tc, partPNoFilter, partQNoFilter, bitDepth, count);
+
+    /// <summary>
+    /// Filters four columns crossing one horizontal chroma boundary.
+    /// </summary>
+    /// <param name="picture">The reconstructed picture.</param>
+    /// <param name="plane">The Cb or Cr component plane.</param>
+    /// <param name="x">The left sample X coordinate.</param>
+    /// <param name="y">The first Q-side sample Y coordinate.</param>
+    /// <param name="tc">The scaled clipping threshold.</param>
+    /// <param name="partPNoFilter">Whether the P-side block retains its original samples.</param>
+    /// <param name="partQNoFilter">Whether the Q-side block retains its original samples.</param>
+    /// <param name="bitDepth">The component sample precision.</param>
+    /// <param name="count">The number of samples in the edge segment.</param>
+    public static void FilterHorizontalChroma(
+        HevcPictureBuffer picture,
+        HevcPlane plane,
+        int x,
+        int y,
+        int tc,
+        bool partPNoFilter,
+        bool partQNoFilter,
+        int bitDepth,
+        int count)
+        => FilterChroma<HorizontalEdgeOperator>(picture, plane, x, y, tc, partPNoFilter, partQNoFilter, bitDepth, count);
+
+    /// <summary>
+    /// Applies the strong or weak luma kernel through one closed edge-orientation operator.
+    /// </summary>
+    /// <typeparam name="TOperator">The vertical or horizontal sample-access operator.</typeparam>
+    /// <param name="picture">The reconstructed picture.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The first Q-side sample X coordinate.</param>
+    /// <param name="y">The first Q-side sample Y coordinate.</param>
+    /// <param name="beta">The scaled discontinuity threshold.</param>
+    /// <param name="tc">The scaled clipping threshold.</param>
+    /// <param name="partPNoFilter">Whether the P-side block retains its original samples.</param>
+    /// <param name="partQNoFilter">Whether the Q-side block retains its original samples.</param>
+    /// <param name="bitDepth">The component sample precision.</param>
+    private static void FilterLuma<TOperator>(
+        HevcPictureBuffer picture,
+        HevcPlane plane,
+        int x,
+        int y,
+        int beta,
+        int tc,
+        bool partPNoFilter,
+        bool partQNoFilter,
+        int bitDepth)
+        where TOperator : struct, IEdgeOperator
+    {
+        if (beta == 0)
+        {
+            return;
+        }
+
+        int p2Start = TOperator.LoadScalar(picture, plane, x, y, -3, 0);
+        int p1Start = TOperator.LoadScalar(picture, plane, x, y, -2, 0);
+        int p0Start = TOperator.LoadScalar(picture, plane, x, y, -1, 0);
+        int q0Start = TOperator.LoadScalar(picture, plane, x, y, 0, 0);
+        int q1Start = TOperator.LoadScalar(picture, plane, x, y, 1, 0);
+        int q2Start = TOperator.LoadScalar(picture, plane, x, y, 2, 0);
+        int p2End = TOperator.LoadScalar(picture, plane, x, y, -3, 3);
+        int p1End = TOperator.LoadScalar(picture, plane, x, y, -2, 3);
+        int p0End = TOperator.LoadScalar(picture, plane, x, y, -1, 3);
+        int q0End = TOperator.LoadScalar(picture, plane, x, y, 0, 3);
+        int q1End = TOperator.LoadScalar(picture, plane, x, y, 1, 3);
+        int q2End = TOperator.LoadScalar(picture, plane, x, y, 2, 3);
+        int dpStart = Math.Abs(p2Start - (2 * p1Start) + p0Start);
+        int dqStart = Math.Abs(q0Start - (2 * q1Start) + q2Start);
+        int dpEnd = Math.Abs(p2End - (2 * p1End) + p0End);
+        int dqEnd = Math.Abs(q0End - (2 * q1End) + q2End);
+        int dp = dpStart + dpEnd;
+        int dq = dqStart + dqEnd;
+        int discontinuity = dp + dq;
+        if (discontinuity >= beta)
+        {
+            return;
+        }
+
+        int sideThreshold = (beta + (beta >> 1)) >> 3;
+        bool filterSecondP = dp < sideThreshold;
+        bool filterSecondQ = dq < sideThreshold;
+        bool strong = UsesStrongFiltering<TOperator>(picture, plane, x, y, 0, 2 * (dpStart + dqStart), beta, tc)
+            && UsesStrongFiltering<TOperator>(picture, plane, x, y, 3, 2 * (dpEnd + dqEnd), beta, tc);
+
+        if (!Vector128.IsHardwareAccelerated)
+        {
+            for (int index = 0; index < 4; index++)
+            {
+                FilterLumaScalar<TOperator>(
+                    picture,
+                    plane,
+                    x,
+                    y,
+                    index,
+                    tc,
+                    strong,
+                    partPNoFilter,
+                    partQNoFilter,
+                    tc * 10,
+                    filterSecondP,
+                    filterSecondQ,
+                    bitDepth);
+            }
+
+            return;
+        }
+
+        Vector128<int> p3 = TOperator.LoadVector(picture, plane, x, y, -4);
+        Vector128<int> p2 = TOperator.LoadVector(picture, plane, x, y, -3);
+        Vector128<int> p1 = TOperator.LoadVector(picture, plane, x, y, -2);
+        Vector128<int> p0 = TOperator.LoadVector(picture, plane, x, y, -1);
+        Vector128<int> q0 = TOperator.LoadVector(picture, plane, x, y, 0);
+        Vector128<int> q1 = TOperator.LoadVector(picture, plane, x, y, 1);
+        Vector128<int> q2 = TOperator.LoadVector(picture, plane, x, y, 2);
+        Vector128<int> q3 = TOperator.LoadVector(picture, plane, x, y, 3);
+
+        // Each Int32 lane is one row or column along the edge. The threshold decision is shared by all four lanes,
+        // while the filter arithmetic stays lane-local and exactly matches the scalar equations below.
+        if (strong)
+        {
+            Vector128<int> twiceTc = Vector128.Create(2 * tc);
+            Vector128<int> four = Vector128.Create(4);
+            Vector128<int> two = Vector128.Create(2);
+            Vector128<int> filteredP0 = Vector128.Clamp((p2 + (p1 * 2) + (p0 * 2) + (q0 * 2) + q1 + four) >> 3, p0 - twiceTc, p0 + twiceTc);
+            Vector128<int> filteredQ0 = Vector128.Clamp((p1 + (p0 * 2) + (q0 * 2) + (q1 * 2) + q2 + four) >> 3, q0 - twiceTc, q0 + twiceTc);
+            Vector128<int> filteredP1 = Vector128.Clamp((p2 + p1 + p0 + q0 + two) >> 2, p1 - twiceTc, p1 + twiceTc);
+            Vector128<int> filteredQ1 = Vector128.Clamp((p0 + q0 + q1 + q2 + two) >> 2, q1 - twiceTc, q1 + twiceTc);
+            Vector128<int> filteredP2 = Vector128.Clamp(((p3 * 2) + (p2 * 3) + p1 + p0 + q0 + four) >> 3, p2 - twiceTc, p2 + twiceTc);
+            Vector128<int> filteredQ2 = Vector128.Clamp((p0 + q0 + q1 + (q2 * 3) + (q3 * 2) + four) >> 3, q2 - twiceTc, q2 + twiceTc);
+
+            TOperator.StoreVector(picture, plane, x, y, -3, partPNoFilter ? p2 : filteredP2, 4);
+            TOperator.StoreVector(picture, plane, x, y, -2, partPNoFilter ? p1 : filteredP1, 4);
+            TOperator.StoreVector(picture, plane, x, y, -1, partPNoFilter ? p0 : filteredP0, 4);
+            TOperator.StoreVector(picture, plane, x, y, 0, partQNoFilter ? q0 : filteredQ0, 4);
+            TOperator.StoreVector(picture, plane, x, y, 1, partQNoFilter ? q1 : filteredQ1, 4);
+            TOperator.StoreVector(picture, plane, x, y, 2, partQNoFilter ? q2 : filteredQ2, 4);
+            return;
+        }
+
+        Vector128<int> primaryDifference = (q0 - p0) * 9;
+        Vector128<int> secondaryDifference = (q1 - p1) * 3;
+        Vector128<int> delta = (primaryDifference - secondaryDifference + Vector128.Create(8)) >> 4;
+        Vector128<int> filterMask = Vector128.LessThan(Vector128.Abs(delta), Vector128.Create(tc * 10));
+        delta = Vector128.Clamp(delta, Vector128.Create(-tc), Vector128.Create(tc));
+        Vector128<int> minimum = Vector128<int>.Zero;
+        Vector128<int> maximum = Vector128.Create((1 << bitDepth) - 1);
+        Vector128<int> filteredP0Weak = Vector128.ConditionalSelect(filterMask, Vector128.Clamp(p0 + delta, minimum, maximum), p0);
+        Vector128<int> filteredQ0Weak = Vector128.ConditionalSelect(filterMask, Vector128.Clamp(q0 - delta, minimum, maximum), q0);
+        TOperator.StoreVector(picture, plane, x, y, -1, partPNoFilter ? p0 : filteredP0Weak, 4);
+        TOperator.StoreVector(picture, plane, x, y, 0, partQNoFilter ? q0 : filteredQ0Weak, 4);
+
+        int halfTc = tc >> 1;
+        if (filterSecondP && !partPNoFilter)
+        {
+            Vector128<int> secondary = (((p2 + p0 + Vector128<int>.One) >> 1) - p1 + delta) >> 1;
+            secondary = Vector128.Clamp(secondary, Vector128.Create(-halfTc), Vector128.Create(halfTc));
+            Vector128<int> filtered = Vector128.ConditionalSelect(filterMask, Vector128.Clamp(p1 + secondary, minimum, maximum), p1);
+            TOperator.StoreVector(picture, plane, x, y, -2, filtered, 4);
+        }
+
+        if (filterSecondQ && !partQNoFilter)
+        {
+            Vector128<int> secondary = (((q2 + q0 + Vector128<int>.One) >> 1) - q1 - delta) >> 1;
+            secondary = Vector128.Clamp(secondary, Vector128.Create(-halfTc), Vector128.Create(halfTc));
+            Vector128<int> filtered = Vector128.ConditionalSelect(filterMask, Vector128.Clamp(q1 + secondary, minimum, maximum), q1);
+            TOperator.StoreVector(picture, plane, x, y, 1, filtered, 4);
+        }
+    }
+
+    /// <summary>
+    /// Applies the chroma kernel through one closed edge-orientation operator.
+    /// </summary>
+    /// <typeparam name="TOperator">The vertical or horizontal sample-access operator.</typeparam>
+    /// <param name="picture">The reconstructed picture.</param>
+    /// <param name="plane">The Cb or Cr component plane.</param>
+    /// <param name="x">The first Q-side sample X coordinate.</param>
+    /// <param name="y">The first Q-side sample Y coordinate.</param>
+    /// <param name="tc">The scaled clipping threshold.</param>
+    /// <param name="partPNoFilter">Whether the P-side block retains its original samples.</param>
+    /// <param name="partQNoFilter">Whether the Q-side block retains its original samples.</param>
+    /// <param name="bitDepth">The component sample precision.</param>
+    /// <param name="count">The number of samples in the edge segment.</param>
+    private static void FilterChroma<TOperator>(
+        HevcPictureBuffer picture,
+        HevcPlane plane,
+        int x,
+        int y,
+        int tc,
+        bool partPNoFilter,
+        bool partQNoFilter,
+        int bitDepth,
+        int count)
+        where TOperator : struct, IEdgeOperator
+    {
+        if (tc == 0)
+        {
+            return;
+        }
+
+        if (!Vector128.IsHardwareAccelerated)
+        {
+            int maximum = (1 << bitDepth) - 1;
+            for (int index = 0; index < count; index++)
+            {
+                int p1 = TOperator.LoadScalar(picture, plane, x, y, -2, index);
+                int p0 = TOperator.LoadScalar(picture, plane, x, y, -1, index);
+                int q0 = TOperator.LoadScalar(picture, plane, x, y, 0, index);
+                int q1 = TOperator.LoadScalar(picture, plane, x, y, 1, index);
+                int delta = Math.Clamp((((q0 - p0) << 2) + p1 - q1 + 4) >> 3, -tc, tc);
+                if (!partPNoFilter)
+                {
+                    TOperator.StoreScalar(picture, plane, x, y, -1, index, Math.Clamp(p0 + delta, 0, maximum));
+                }
+
+                if (!partQNoFilter)
+                {
+                    TOperator.StoreScalar(picture, plane, x, y, 0, index, Math.Clamp(q0 - delta, 0, maximum));
+                }
+            }
+
+            return;
+        }
+
+        Vector128<int> p1Vector = TOperator.LoadVector(picture, plane, x, y, -2);
+        Vector128<int> p0Vector = TOperator.LoadVector(picture, plane, x, y, -1);
+        Vector128<int> q0Vector = TOperator.LoadVector(picture, plane, x, y, 0);
+        Vector128<int> q1Vector = TOperator.LoadVector(picture, plane, x, y, 1);
+        Vector128<int> deltaVector = (((q0Vector - p0Vector) * 4) + p1Vector - q1Vector + Vector128.Create(4)) >> 3;
+        deltaVector = Vector128.Clamp(deltaVector, Vector128.Create(-tc), Vector128.Create(tc));
+        Vector128<int> minimum = Vector128<int>.Zero;
+        Vector128<int> maximumVector = Vector128.Create((1 << bitDepth) - 1);
+
+        if (!partPNoFilter)
+        {
+            TOperator.StoreVector(picture, plane, x, y, -1, Vector128.Clamp(p0Vector + deltaVector, minimum, maximumVector), count);
+        }
+
+        if (!partQNoFilter)
+        {
+            TOperator.StoreVector(picture, plane, x, y, 0, Vector128.Clamp(q0Vector - deltaVector, minimum, maximumVector), count);
+        }
+    }
+
+    /// <summary>
+    /// Applies the scalar luma equations to one sample along an edge.
+    /// </summary>
+    /// <typeparam name="TOperator">The vertical or horizontal sample-access operator.</typeparam>
+    /// <param name="picture">The reconstructed picture.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The first Q-side sample X coordinate.</param>
+    /// <param name="y">The first Q-side sample Y coordinate.</param>
+    /// <param name="index">The sample offset along the edge.</param>
+    /// <param name="tc">The scaled clipping threshold.</param>
+    /// <param name="strong">Whether the strong six-sample filter is selected.</param>
+    /// <param name="partPNoFilter">Whether the P-side block retains its original samples.</param>
+    /// <param name="partQNoFilter">Whether the Q-side block retains its original samples.</param>
+    /// <param name="thresholdCut">The weak-filter delta threshold.</param>
+    /// <param name="filterSecondP">Whether the second P-side sample is filtered.</param>
+    /// <param name="filterSecondQ">Whether the second Q-side sample is filtered.</param>
+    /// <param name="bitDepth">The component sample precision.</param>
+    private static void FilterLumaScalar<TOperator>(
+        HevcPictureBuffer picture,
+        HevcPlane plane,
+        int x,
+        int y,
+        int index,
+        int tc,
+        bool strong,
+        bool partPNoFilter,
+        bool partQNoFilter,
+        int thresholdCut,
+        bool filterSecondP,
+        bool filterSecondQ,
+        int bitDepth)
+        where TOperator : struct, IEdgeOperator
+    {
+        int p3 = TOperator.LoadScalar(picture, plane, x, y, -4, index);
+        int p2 = TOperator.LoadScalar(picture, plane, x, y, -3, index);
+        int p1 = TOperator.LoadScalar(picture, plane, x, y, -2, index);
+        int p0 = TOperator.LoadScalar(picture, plane, x, y, -1, index);
+        int q0 = TOperator.LoadScalar(picture, plane, x, y, 0, index);
+        int q1 = TOperator.LoadScalar(picture, plane, x, y, 1, index);
+        int q2 = TOperator.LoadScalar(picture, plane, x, y, 2, index);
+        int q3 = TOperator.LoadScalar(picture, plane, x, y, 3, index);
+        if (strong)
+        {
+            if (!partPNoFilter)
+            {
+                int filteredP0 = Math.Clamp(
+                    (p2 + (2 * p1) + (2 * p0) + (2 * q0) + q1 + 4) >> 3,
+                    p0 - (2 * tc),
+                    p0 + (2 * tc));
+
+                TOperator.StoreScalar(picture, plane, x, y, -1, index, filteredP0);
+                TOperator.StoreScalar(picture, plane, x, y, -2, index, Math.Clamp((p2 + p1 + p0 + q0 + 2) >> 2, p1 - (2 * tc), p1 + (2 * tc)));
+                TOperator.StoreScalar(picture, plane, x, y, -3, index, Math.Clamp(((2 * p3) + (3 * p2) + p1 + p0 + q0 + 4) >> 3, p2 - (2 * tc), p2 + (2 * tc)));
+            }
+
+            if (!partQNoFilter)
+            {
+                int filteredQ0 = Math.Clamp(
+                    (p1 + (2 * p0) + (2 * q0) + (2 * q1) + q2 + 4) >> 3,
+                    q0 - (2 * tc),
+                    q0 + (2 * tc));
+
+                TOperator.StoreScalar(picture, plane, x, y, 0, index, filteredQ0);
+                TOperator.StoreScalar(picture, plane, x, y, 1, index, Math.Clamp((p0 + q0 + q1 + q2 + 2) >> 2, q1 - (2 * tc), q1 + (2 * tc)));
+                TOperator.StoreScalar(picture, plane, x, y, 2, index, Math.Clamp((p0 + q0 + q1 + (3 * q2) + (2 * q3) + 4) >> 3, q2 - (2 * tc), q2 + (2 * tc)));
+            }
+
+            return;
+        }
+
+        int delta = ((9 * (q0 - p0)) - (3 * (q1 - p1)) + 8) >> 4;
+        if (Math.Abs(delta) >= thresholdCut)
+        {
+            return;
+        }
+
+        delta = Math.Clamp(delta, -tc, tc);
+        int maximum = (1 << bitDepth) - 1;
+        if (!partPNoFilter)
+        {
+            TOperator.StoreScalar(picture, plane, x, y, -1, index, Math.Clamp(p0 + delta, 0, maximum));
+            if (filterSecondP)
+            {
+                int secondary = (((p2 + p0 + 1) >> 1) - p1 + delta) >> 1;
+                secondary = Math.Clamp(secondary, -(tc >> 1), tc >> 1);
+                TOperator.StoreScalar(picture, plane, x, y, -2, index, Math.Clamp(p1 + secondary, 0, maximum));
+            }
+        }
+
+        if (!partQNoFilter)
+        {
+            TOperator.StoreScalar(picture, plane, x, y, 0, index, Math.Clamp(q0 - delta, 0, maximum));
+            if (filterSecondQ)
+            {
+                int secondary = (((q2 + q0 + 1) >> 1) - q1 - delta) >> 1;
+                secondary = Math.Clamp(secondary, -(tc >> 1), tc >> 1);
+                TOperator.StoreScalar(picture, plane, x, y, 1, index, Math.Clamp(q1 + secondary, 0, maximum));
+            }
+        }
+    }
+
+    /// <summary>
+    /// Determines whether one endpoint satisfies the strong-filter conditions.
+    /// </summary>
+    /// <typeparam name="TOperator">The vertical or horizontal sample-access operator.</typeparam>
+    /// <param name="picture">The reconstructed picture.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The first Q-side sample X coordinate.</param>
+    /// <param name="y">The first Q-side sample Y coordinate.</param>
+    /// <param name="index">The endpoint offset along the edge.</param>
+    /// <param name="discontinuity">Twice the endpoint's second-derivative sum.</param>
+    /// <param name="beta">The scaled discontinuity threshold.</param>
+    /// <param name="tc">The scaled clipping threshold.</param>
+    /// <returns><see langword="true"/> when strong filtering is permitted; otherwise, <see langword="false"/>.</returns>
+    private static bool UsesStrongFiltering<TOperator>(
+        HevcPictureBuffer picture,
+        HevcPlane plane,
+        int x,
+        int y,
+        int index,
+        int discontinuity,
+        int beta,
+        int tc)
+        where TOperator : struct, IEdgeOperator
+    {
+        int p3 = TOperator.LoadScalar(picture, plane, x, y, -4, index);
+        int p0 = TOperator.LoadScalar(picture, plane, x, y, -1, index);
+        int q0 = TOperator.LoadScalar(picture, plane, x, y, 0, index);
+        int q3 = TOperator.LoadScalar(picture, plane, x, y, 3, index);
+        int strongDiscontinuity = Math.Abs(p3 - p0) + Math.Abs(q3 - q0);
+        int strongThreshold = ((5 * tc) + 1) >> 1;
+        return strongDiscontinuity < (beta >> 3)
+            && discontinuity < (beta >> 2)
+            && Math.Abs(p0 - q0) < strongThreshold;
+    }
+
+    /// <summary>
+    /// Accesses four rows across a vertical edge.
+    /// </summary>
+    private readonly struct VerticalEdgeOperator : IEdgeOperator
+    {
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector128<int> LoadVector(HevcPictureBuffer picture, HevcPlane plane, int x, int y, int distance)
+            => Vector128.Create(
+                (int)picture.GetRowSpan(plane, y)[x + distance],
+                picture.GetRowSpan(plane, y + 1)[x + distance],
+                picture.GetRowSpan(plane, y + 2)[x + distance],
+                picture.GetRowSpan(plane, y + 3)[x + distance]);
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void StoreVector(
+            HevcPictureBuffer picture,
+            HevcPlane plane,
+            int x,
+            int y,
+            int distance,
+            Vector128<int> value,
+            int count)
+        {
+            for (int index = 0; index < count; index++)
+            {
+                picture.GetRowSpan(plane, y + index)[x + distance] = (ushort)value.GetElement(index);
+            }
+        }
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int LoadScalar(HevcPictureBuffer picture, HevcPlane plane, int x, int y, int distance, int index)
+            => picture.GetRowSpan(plane, y + index)[x + distance];
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void StoreScalar(HevcPictureBuffer picture, HevcPlane plane, int x, int y, int distance, int index, int value)
+            => picture.GetRowSpan(plane, y + index)[x + distance] = (ushort)value;
+    }
+
+    /// <summary>
+    /// Accesses four columns across a horizontal edge.
+    /// </summary>
+    private readonly struct HorizontalEdgeOperator : IEdgeOperator
+    {
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector128<int> LoadVector(HevcPictureBuffer picture, HevcPlane plane, int x, int y, int distance)
+        {
+            ref ushort source = ref picture.GetRowSpan(plane, y + distance)[x];
+            Vector64<ushort> packed = Unsafe.As<ushort, Vector64<ushort>>(ref source);
+            return Vector128.WidenLower(Vector128.Create(packed, Vector64<ushort>.Zero)).AsInt32();
+        }
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void StoreVector(
+            HevcPictureBuffer picture,
+            HevcPlane plane,
+            int x,
+            int y,
+            int distance,
+            Vector128<int> value,
+            int count)
+        {
+            ref ushort destination = ref picture.GetRowSpan(plane, y + distance)[x];
+            if (count == 4)
+            {
+                Vector64<ushort> packed = Vector128.Narrow(value, Vector128<int>.Zero).AsUInt16().GetLower();
+                Unsafe.As<ushort, Vector64<ushort>>(ref destination) = packed;
+                return;
+            }
+
+            destination = (ushort)value.GetElement(0);
+            Unsafe.Add(ref destination, 1) = (ushort)value.GetElement(1);
+        }
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int LoadScalar(HevcPictureBuffer picture, HevcPlane plane, int x, int y, int distance, int index)
+            => picture.GetRowSpan(plane, y + distance)[x + index];
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void StoreScalar(HevcPictureBuffer picture, HevcPlane plane, int x, int y, int distance, int index, int value)
+            => picture.GetRowSpan(plane, y + distance)[x + index] = (ushort)value;
+    }
+}

src/ImageSharp/Formats/Heif/Hevc/HevcDeblockingState.cs

@@ -0,0 +1,118 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <summary>
+/// Tracks luma transform and prediction boundaries at the four-sample resolution used to derive HEVC deblocking edges.
+/// </summary>
+internal sealed class HevcDeblockingState : IDisposable
+{
+    /// <summary>
+    /// The base-two logarithm of the boundary-map unit side.
+    /// </summary>
+    private const int UnitLog2 = 2;
+
+    /// <summary>
+    /// The packed flag identifying a vertical boundary at a unit's left edge.
+    /// </summary>
+    private const byte VerticalBoundary = 1 << 0;
+
+    /// <summary>
+    /// The packed flag identifying a horizontal boundary at a unit's top edge.
+    /// </summary>
+    private const byte HorizontalBoundary = 1 << 1;
+
+    /// <summary>
+    /// The boundary maps for the primary plane of combined coding or each independently coded color plane.
+    /// </summary>
+    private readonly Buffer2D<byte>[] boundaries;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcDeblockingState"/> class.
+    /// </summary>
+    /// <param name="configuration">The configuration providing the image memory allocator.</param>
+    /// <param name="sequenceParameterSet">The coded picture dimensions.</param>
+    public HevcDeblockingState(Configuration configuration, HevcSequenceParameterSet sequenceParameterSet)
+    {
+        int width = DivideCeilingByPowerOfTwo(sequenceParameterSet.Width, UnitLog2);
+        int height = DivideCeilingByPowerOfTwo(sequenceParameterSet.Height, UnitLog2);
+        this.boundaries =
+        [
+            configuration.MemoryAllocator.Allocate2D<byte>(width, height),
+            configuration.MemoryAllocator.Allocate2D<byte>(width, height),
+            configuration.MemoryAllocator.Allocate2D<byte>(width, height),
+        ];
+    }
+
+    /// <summary>
+    /// Records the left and top edges of one leaf transform or pulse-code-modulated coding block.
+    /// </summary>
+    /// <param name="plane">The primary coding plane.</param>
+    /// <param name="x">The block left coordinate in full-resolution primary-plane samples.</param>
+    /// <param name="y">The block top coordinate in full-resolution primary-plane samples.</param>
+    /// <param name="width">The block width in samples.</param>
+    /// <param name="height">The block height in samples.</param>
+    public void MarkBlock(HevcPlane plane, int x, int y, int width, int height)
+    {
+        Buffer2D<byte> map = this.boundaries[(int)plane];
+        int unitX = x >> UnitLog2;
+        int unitY = y >> UnitLog2;
+        int endX = Math.Min(DivideCeilingByPowerOfTwo(x + width, UnitLog2), map.Width);
+        int endY = Math.Min(DivideCeilingByPowerOfTwo(y + height, UnitLog2), map.Height);
+
+        // A transform boundary covers every four-sample segment along its edge. Packing both orientations into one
+        // byte keeps the decoder state contiguous and lets the later eight-sample deblocking traversal reject edges cheaply.
+        for (int row = unitY; row < endY; row++)
+        {
+            map.DangerousGetRowSpan(row)[unitX] |= VerticalBoundary;
+        }
+
+        Span<byte> top = map.DangerousGetRowSpan(unitY);
+        for (int column = unitX; column < endX; column++)
+        {
+            top[column] |= HorizontalBoundary;
+        }
+    }
+
+    /// <summary>
+    /// Gets whether a four-sample segment begins at a vertical transform or prediction boundary.
+    /// </summary>
+    /// <param name="plane">The primary coding plane.</param>
+    /// <param name="x">The segment left coordinate in full-resolution primary-plane samples.</param>
+    /// <param name="y">The segment top coordinate in full-resolution primary-plane samples.</param>
+    /// <returns><see langword="true"/> when the segment is a vertical boundary; otherwise, <see langword="false"/>.</returns>
+    public bool IsVerticalBoundary(HevcPlane plane, int x, int y)
+        => (this.boundaries[(int)plane].DangerousGetRowSpan(y >> UnitLog2)[x >> UnitLog2] & VerticalBoundary) != 0;
+
+    /// <summary>
+    /// Gets whether a four-sample segment begins at a horizontal transform or prediction boundary.
+    /// </summary>
+    /// <param name="plane">The primary coding plane.</param>
+    /// <param name="x">The segment left coordinate in full-resolution primary-plane samples.</param>
+    /// <param name="y">The segment top coordinate in full-resolution primary-plane samples.</param>
+    /// <returns><see langword="true"/> when the segment is a horizontal boundary; otherwise, <see langword="false"/>.</returns>
+    public bool IsHorizontalBoundary(HevcPlane plane, int x, int y)
+        => (this.boundaries[(int)plane].DangerousGetRowSpan(y >> UnitLog2)[x >> UnitLog2] & HorizontalBoundary) != 0;
+
+    /// <summary>
+    /// Releases the allocator-owned boundary maps.
+    /// </summary>
+    public void Dispose()
+    {
+        foreach (Buffer2D<byte> map in this.boundaries)
+        {
+            map.Dispose();
+        }
+    }
+
+    /// <summary>
+    /// Divides a nonnegative sample count by a power of two with upward rounding.
+    /// </summary>
+    /// <param name="value">The sample count.</param>
+    /// <param name="shift">The base-two divisor logarithm.</param>
+    /// <returns>The upward-rounded quotient.</returns>
+    private static int DivideCeilingByPowerOfTwo(int value, int shift) => (value + (1 << shift) - 1) >> shift;
+}

src/ImageSharp/Formats/Heif/Hevc/HevcInverseTransformer.Operations.cs

@@ -422,7 +422,7 @@ internal static partial class HevcInverseTransformer
     /// <param name="width">The transform-block width.</param>
     /// <param name="height">The transform-block height.</param>
     /// <param name="bitDepth">The reconstructed component precision.</param>
-    private static void AddResidual(ReadOnlySpan<int> residual, Span<ushort> destination, int destinationStride, int width, int height, int bitDepth)
+    public static void AddResidual(ReadOnlySpan<int> residual, Span<ushort> destination, int destinationStride, int width, int height, int bitDepth)
     {
         int maximum = (1 << bitDepth) - 1;
         for (int y = 0; y < height; y++)

src/ImageSharp/Formats/Heif/Hevc/HevcPictureBuffer.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Numerics;
 using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
@@ -33,7 +34,8 @@ internal sealed class HevcPictureBuffer : IDisposable
             sequenceParameterSet.BitDepthLuma,
             sequenceParameterSet.BitDepthChroma,
             sequenceParameterSet.ChromaFormat,
-            sequenceParameterSet.SeparateColorPlaneFlag)
+            sequenceParameterSet.SeparateColorPlaneFlag,
+            1 << sequenceParameterSet.MinCodingBlockLog2)
     {
     }
 
@@ -47,6 +49,7 @@ internal sealed class HevcPictureBuffer : IDisposable
     /// <param name="bitDepthChroma">The chroma sample precision.</param>
     /// <param name="chromaFormat">The HEVC chroma-format identifier.</param>
     /// <param name="separateColorPlane">Whether 4:4:4 components are coded as separate color planes.</param>
+    /// <param name="storageAlignment">The luma sample alignment applied to the owned reconstruction planes.</param>
     public HevcPictureBuffer(
         Configuration configuration,
         int width,
@@ -54,7 +57,8 @@ internal sealed class HevcPictureBuffer : IDisposable
         int bitDepthLuma,
         int bitDepthChroma,
         byte chromaFormat,
-        bool separateColorPlane)
+        bool separateColorPlane,
+        int storageAlignment = 1)
     {
         this.Width = width;
         this.Height = height;
@@ -66,11 +70,13 @@ internal sealed class HevcPictureBuffer : IDisposable
         // Separate color planes are independently coded at full resolution even though chroma_format_idc is 4:4:4.
         this.chromaSubsamplingX = !this.SeparateColorPlane && this.ChromaFormat is 1 or 2 ? 1 : 0;
         this.chromaSubsamplingY = !this.SeparateColorPlane && this.ChromaFormat == 1 ? 1 : 0;
-        this.Luma = configuration.MemoryAllocator.Allocate2D<ushort>(this.Width, this.Height);
+        int storageWidth = DivideCeilingByPowerOfTwo(this.Width, BitOperations.Log2((uint)storageAlignment)) * storageAlignment;
+        int storageHeight = DivideCeilingByPowerOfTwo(this.Height, BitOperations.Log2((uint)storageAlignment)) * storageAlignment;
+        this.Luma = configuration.MemoryAllocator.Allocate2D<ushort>(storageWidth, storageHeight);
         if (this.ChromaFormat != 0)
         {
-            int chromaWidth = DivideCeilingByPowerOfTwo(this.Width, this.chromaSubsamplingX);
-            int chromaHeight = DivideCeilingByPowerOfTwo(this.Height, this.chromaSubsamplingY);
+            int chromaWidth = DivideCeilingByPowerOfTwo(storageWidth, this.chromaSubsamplingX);
+            int chromaHeight = DivideCeilingByPowerOfTwo(storageHeight, this.chromaSubsamplingY);
 
             this.ChromaBlue = configuration.MemoryAllocator.Allocate2D<ushort>(chromaWidth, chromaHeight);
             this.ChromaRed = configuration.MemoryAllocator.Allocate2D<ushort>(chromaWidth, chromaHeight);
@@ -171,6 +177,25 @@ internal sealed class HevcPictureBuffer : IDisposable
             _ => this.ChromaRed!.DangerousGetRowSpan(row),
         };
 
+    /// <summary>
+    /// Copies the complete coded component planes to another picture buffer with the same dimensions and chroma layout.
+    /// </summary>
+    /// <param name="destination">The destination picture buffer.</param>
+    public void CopyTo(HevcPictureBuffer destination)
+    {
+        int planeCount = this.ChromaFormat == 0 ? 1 : 3;
+        for (int planeIndex = 0; planeIndex < planeCount; planeIndex++)
+        {
+            HevcPlane plane = (HevcPlane)planeIndex;
+            int width = this.GetWidth(plane);
+            int height = this.GetHeight(plane);
+            for (int row = 0; row < height; row++)
+            {
+                this.GetRowSpan(plane, row)[..width].CopyTo(destination.GetRowSpan(plane, row));
+            }
+        }
+    }
+
     /// <summary>
     /// Releases the owned luma and chroma plane allocations.
     /// </summary>

src/ImageSharp/Formats/Heif/Hevc/HevcPictureDecoder.Deblocking.cs

@@ -0,0 +1,390 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <content>
+/// Implements picture-level HEVC deblocking traversal and threshold derivation.
+/// </content>
+internal sealed partial class HevcPictureDecoder
+{
+    /// <summary>
+    /// Defines the orientation-dependent boundary lookup and four-sample filter dispatch.
+    /// </summary>
+    private interface IDeblockingDirection
+    {
+        /// <summary>
+        /// Gets a value indicating whether the boundary is vertical.
+        /// </summary>
+        public static abstract bool IsVertical { get; }
+
+        /// <summary>
+        /// Gets whether the selected four-sample segment is a transform or prediction boundary.
+        /// </summary>
+        /// <param name="state">The decoded deblocking boundary state.</param>
+        /// <param name="plane">The primary coding plane.</param>
+        /// <param name="x">The segment left luma coordinate.</param>
+        /// <param name="y">The segment top luma coordinate.</param>
+        /// <returns><see langword="true"/> when the segment is a filter candidate; otherwise, <see langword="false"/>.</returns>
+        public static abstract bool IsBoundary(HevcDeblockingState state, HevcPlane plane, int x, int y);
+
+        /// <summary>
+        /// Applies the orientation-specific luma kernel.
+        /// </summary>
+        /// <param name="picture">The reconstructed picture.</param>
+        /// <param name="plane">The component plane.</param>
+        /// <param name="x">The first Q-side sample X coordinate.</param>
+        /// <param name="y">The first Q-side sample Y coordinate.</param>
+        /// <param name="beta">The scaled discontinuity threshold.</param>
+        /// <param name="tc">The scaled clipping threshold.</param>
+        /// <param name="partPNoFilter">Whether the P-side block retains its original samples.</param>
+        /// <param name="partQNoFilter">Whether the Q-side block retains its original samples.</param>
+        /// <param name="bitDepth">The component sample precision.</param>
+        public static abstract void FilterLuma(
+            HevcPictureBuffer picture,
+            HevcPlane plane,
+            int x,
+            int y,
+            int beta,
+            int tc,
+            bool partPNoFilter,
+            bool partQNoFilter,
+            int bitDepth);
+
+        /// <summary>
+        /// Applies the orientation-specific chroma kernel.
+        /// </summary>
+        /// <param name="picture">The reconstructed picture.</param>
+        /// <param name="plane">The Cb or Cr component plane.</param>
+        /// <param name="x">The first Q-side sample X coordinate.</param>
+        /// <param name="y">The first Q-side sample Y coordinate.</param>
+        /// <param name="tc">The scaled clipping threshold.</param>
+        /// <param name="partPNoFilter">Whether the P-side block retains its original samples.</param>
+        /// <param name="partQNoFilter">Whether the Q-side block retains its original samples.</param>
+        /// <param name="bitDepth">The component sample precision.</param>
+        /// <param name="count">The number of samples in the edge segment.</param>
+        public static abstract void FilterChroma(
+            HevcPictureBuffer picture,
+            HevcPlane plane,
+            int x,
+            int y,
+            int tc,
+            bool partPNoFilter,
+            bool partQNoFilter,
+            int bitDepth,
+            int count);
+    }
+
+    /// <summary>
+    /// Gets the H.265 Table 8-20 clipping thresholds indexed by the effective boundary quantization parameter.
+    /// </summary>
+    private static ReadOnlySpan<byte> DeblockingTcTable =>
+    [
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4,
+        4, 4, 5, 5, 6, 6, 7, 8, 9, 10, 11, 13, 14, 16, 18, 20, 22, 24,
+    ];
+
+    /// <summary>
+    /// Gets the H.265 Table 8-20 discontinuity thresholds indexed by the effective boundary quantization parameter.
+    /// </summary>
+    private static ReadOnlySpan<byte> DeblockingBetaTable =>
+    [
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 22, 24, 26,
+        28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64,
+    ];
+
+    /// <summary>
+    /// Applies vertical edges across the complete picture before applying any horizontal edge.
+    /// </summary>
+    /// <param name="tileLayout">The picture tile mapping.</param>
+    private void ApplyDeblockingFilter(in HevcTileLayout tileLayout)
+    {
+        this.ApplyDeblockingDirection<VerticalDeblockingDirection>(in tileLayout);
+        this.ApplyDeblockingDirection<HorizontalDeblockingDirection>(in tileLayout);
+    }
+
+    /// <summary>
+    /// Applies one closed deblocking direction to every coded component plane.
+    /// </summary>
+    /// <typeparam name="TDirection">The vertical or horizontal boundary operator.</typeparam>
+    /// <param name="tileLayout">The picture tile mapping.</param>
+    private void ApplyDeblockingDirection<TDirection>(in HevcTileLayout tileLayout)
+        where TDirection : struct, IDeblockingDirection
+    {
+        if (this.sequenceParameterSet.SeparateColorPlaneFlag)
+        {
+            for (int planeIndex = 0; planeIndex < 3; planeIndex++)
+            {
+                this.ApplyLumaDeblocking<TDirection>((HevcPlane)planeIndex, planeIndex, in tileLayout);
+            }
+
+            return;
+        }
+
+        this.ApplyLumaDeblocking<TDirection>(HevcPlane.Y, 0, in tileLayout);
+        if (this.sequenceParameterSet.ChromaFormat != 0)
+        {
+            this.ApplyChromaDeblocking<TDirection>(HevcPlane.Cb, in tileLayout);
+            this.ApplyChromaDeblocking<TDirection>(HevcPlane.Cr, in tileLayout);
+        }
+    }
+
+    /// <summary>
+    /// Applies one deblocking direction with the luma kernel to a primary coded plane.
+    /// </summary>
+    /// <typeparam name="TDirection">The vertical or horizontal boundary operator.</typeparam>
+    /// <param name="plane">The primary coded plane.</param>
+    /// <param name="codingTreeStateIndex">The coding-tree state selected for the plane.</param>
+    /// <param name="tileLayout">The picture tile mapping.</param>
+    private void ApplyLumaDeblocking<TDirection>(HevcPlane plane, int codingTreeStateIndex, in HevcTileLayout tileLayout)
+        where TDirection : struct, IDeblockingDirection
+    {
+        int width = this.Picture.GetWidth(plane);
+        int height = this.Picture.GetHeight(plane);
+        int acrossLimit = TDirection.IsVertical ? width : height;
+        int alongLimit = TDirection.IsVertical ? height : width;
+        int bitDepth = this.Picture.GetBitDepth(plane);
+        int bitDepthScale = 1 << (bitDepth - 8);
+        int codingTreeBlockSize = 1 << this.sequenceParameterSet.CodingTreeBlockLog2;
+        HevcCodingTreeState codingTreeState = this.codingTreeStates[codingTreeStateIndex];
+
+        // Deblocking visits only eight-sample grid lines, but each candidate is retained at four-sample resolution
+        // because transform and prediction boundaries can differ between the two halves of that grid interval.
+        for (int edge = 8; edge < acrossLimit; edge += 8)
+        {
+            for (int along = 0; along < alongLimit; along += 4)
+            {
+                int x = TDirection.IsVertical ? edge : along;
+                int y = TDirection.IsVertical ? along : edge;
+                if (!TDirection.IsBoundary(this.deblockingState, plane, x, y))
+                {
+                    continue;
+                }
+
+                int rasterAddress = ((y / codingTreeBlockSize) * tileLayout.Width) + (x / codingTreeBlockSize);
+                HevcLoopFilterRegion region = this.sampleAdaptiveOffsetState.GetLoopFilterRegion(rasterAddress, plane);
+                if (region.DeblockingFilterDisabled
+                    || !this.IsDeblockingCtbBoundaryAvailable<TDirection>(rasterAddress, plane, x, y, codingTreeBlockSize, in tileLayout))
+                {
+                    continue;
+                }
+
+                int pX = x - (TDirection.IsVertical ? 1 : 0);
+                int pY = y - (TDirection.IsVertical ? 0 : 1);
+                int qX = x;
+                int qY = y;
+                int quantizationParameterP = codingTreeState.GetQuantizationParameter(pX, pY);
+                int quantizationParameterQ = codingTreeState.GetQuantizationParameter(qX, qY);
+                int averageQuantizationParameter = (quantizationParameterP + quantizationParameterQ + 1) >> 1;
+                int tcIndex = Math.Clamp(averageQuantizationParameter + 2 + (region.DeblockingFilterTcOffsetDiv2 << 1), 0, 53);
+                int betaIndex = Math.Clamp(averageQuantizationParameter + (region.DeblockingFilterBetaOffsetDiv2 << 1), 0, 51);
+                int tc = DeblockingTcTable[tcIndex] * bitDepthScale;
+                int beta = DeblockingBetaTable[betaIndex] * bitDepthScale;
+                bool partPNoFilter = this.IsDeblockingSuppressed(codingTreeState, pX, pY);
+                bool partQNoFilter = this.IsDeblockingSuppressed(codingTreeState, qX, qY);
+
+                TDirection.FilterLuma(this.Picture, plane, x, y, beta, tc, partPNoFilter, partQNoFilter, bitDepth);
+            }
+        }
+    }
+
+    /// <summary>
+    /// Applies one deblocking direction with the chroma kernel to a combined Cb or Cr plane.
+    /// </summary>
+    /// <typeparam name="TDirection">The vertical or horizontal boundary operator.</typeparam>
+    /// <param name="plane">The Cb or Cr component plane.</param>
+    /// <param name="tileLayout">The picture tile mapping.</param>
+    private void ApplyChromaDeblocking<TDirection>(HevcPlane plane, in HevcTileLayout tileLayout)
+        where TDirection : struct, IDeblockingDirection
+    {
+        int subsamplingX = this.Picture.GetSubsamplingX(plane);
+        int subsamplingY = this.Picture.GetSubsamplingY(plane);
+        int width = this.Picture.GetWidth(plane);
+        int height = this.Picture.GetHeight(plane);
+        int acrossLimit = TDirection.IsVertical ? width : height;
+        int alongLimit = TDirection.IsVertical ? height : width;
+        int alongSubsampling = TDirection.IsVertical ? subsamplingY : subsamplingX;
+        int segmentLength = 4 >> alongSubsampling;
+        int bitDepth = this.Picture.GetBitDepth(plane);
+        int bitDepthScale = 1 << (bitDepth - 8);
+        int codingTreeBlockSize = 1 << this.sequenceParameterSet.CodingTreeBlockLog2;
+        HevcCodingTreeState codingTreeState = this.codingTreeStates[0];
+
+        // Chroma deblocking uses eight-sample component-grid edges. A two-lane segment in subsampled directions still
+        // enters the SIMD kernel, but only its valid low lanes are committed because QP and suppression state can change next.
+        for (int edge = 8; edge < acrossLimit; edge += 8)
+        {
+            for (int along = 0; along < alongLimit; along += segmentLength)
+            {
+                int x = TDirection.IsVertical ? edge : along;
+                int y = TDirection.IsVertical ? along : edge;
+                int lumaX = x << subsamplingX;
+                int lumaY = y << subsamplingY;
+                if (!TDirection.IsBoundary(this.deblockingState, HevcPlane.Y, lumaX, lumaY))
+                {
+                    continue;
+                }
+
+                int rasterAddress = ((lumaY / codingTreeBlockSize) * tileLayout.Width) + (lumaX / codingTreeBlockSize);
+                HevcLoopFilterRegion region = this.sampleAdaptiveOffsetState.GetLoopFilterRegion(rasterAddress, HevcPlane.Y);
+                if (region.DeblockingFilterDisabled
+                    || !this.IsDeblockingCtbBoundaryAvailable<TDirection>(
+                        rasterAddress,
+                        HevcPlane.Y,
+                        lumaX,
+                        lumaY,
+                        codingTreeBlockSize,
+                        in tileLayout))
+                {
+                    continue;
+                }
+
+                int pX = lumaX - (TDirection.IsVertical ? 1 : 0);
+                int pY = lumaY - (TDirection.IsVertical ? 0 : 1);
+                int qX = lumaX;
+                int qY = lumaY;
+                int quantizationParameterP = codingTreeState.GetQuantizationParameter(pX, pY);
+                int quantizationParameterQ = codingTreeState.GetQuantizationParameter(qX, qY);
+                int averageQuantizationParameter = (quantizationParameterP + quantizationParameterQ + 1) >> 1;
+                int componentOffset = codingTreeState.GetChromaQuantizationOffset(plane, qX, qY);
+                int chromaQuantizationParameter = HevcQuantizationParameters.GetChromaQuantizationParameter(
+                    averageQuantizationParameter,
+                    componentOffset,
+                    0,
+                    this.sequenceParameterSet.ChromaFormat);
+
+                int tcIndex = Math.Clamp(chromaQuantizationParameter + 2 + (region.DeblockingFilterTcOffsetDiv2 << 1), 0, 53);
+                int tc = DeblockingTcTable[tcIndex] * bitDepthScale;
+                bool partPNoFilter = this.IsDeblockingSuppressed(codingTreeState, pX, pY);
+                bool partQNoFilter = this.IsDeblockingSuppressed(codingTreeState, qX, qY);
+
+                TDirection.FilterChroma(this.Picture, plane, x, y, tc, partPNoFilter, partQNoFilter, bitDepth, segmentLength);
+            }
+        }
+    }
+
+    /// <summary>
+    /// Gets whether an edge crossing a coding-tree-block boundary is permitted by slice and tile rules.
+    /// </summary>
+    /// <typeparam name="TDirection">The vertical or horizontal boundary operator.</typeparam>
+    /// <param name="rasterAddress">The Q-side coding-tree-block raster address.</param>
+    /// <param name="plane">The primary coding plane.</param>
+    /// <param name="x">The edge luma X coordinate.</param>
+    /// <param name="y">The edge luma Y coordinate.</param>
+    /// <param name="codingTreeBlockSize">The coding-tree-block side in luma samples.</param>
+    /// <param name="tileLayout">The picture tile mapping.</param>
+    /// <returns><see langword="true"/> for an internal or permitted external boundary; otherwise, <see langword="false"/>.</returns>
+    private bool IsDeblockingCtbBoundaryAvailable<TDirection>(
+        int rasterAddress,
+        HevcPlane plane,
+        int x,
+        int y,
+        int codingTreeBlockSize,
+        in HevcTileLayout tileLayout)
+        where TDirection : struct, IDeblockingDirection
+    {
+        int acrossCoordinate = TDirection.IsVertical ? x : y;
+        if (acrossCoordinate % codingTreeBlockSize != 0)
+        {
+            return true;
+        }
+
+        HevcLoopFilterBoundaryAvailability availability = this.sampleAdaptiveOffsetState.GetLoopFilterBoundaryAvailability(
+            rasterAddress,
+            plane,
+            tileLayout.Width,
+            tileLayout.Height,
+            this.pictureParameterSet.LoopFilterAcrossTilesEnabled);
+
+        return TDirection.IsVertical ? availability.Left : availability.Above;
+    }
+
+    /// <summary>
+    /// Gets whether PCM or transform-bypass syntax preserves one side of a filtered boundary.
+    /// </summary>
+    /// <param name="state">The coding-tree state for the selected primary plane.</param>
+    /// <param name="x">The luma sample X coordinate.</param>
+    /// <param name="y">The luma sample Y coordinate.</param>
+    /// <returns><see langword="true"/> when the reconstructed side must not be modified; otherwise, <see langword="false"/>.</returns>
+    private bool IsDeblockingSuppressed(HevcCodingTreeState state, int x, int y)
+        => (this.sequenceParameterSet.PcmLoopFilterDisabled && state.IsPcm(x, y))
+            || (this.pictureParameterSet.TransquantizationBypassEnabled && state.IsTransquantBypass(x, y));
+
+    /// <summary>
+    /// Selects vertical boundary lookup and filtering.
+    /// </summary>
+    private readonly struct VerticalDeblockingDirection : IDeblockingDirection
+    {
+        /// <inheritdoc/>
+        public static bool IsVertical => true;
+
+        /// <inheritdoc/>
+        public static bool IsBoundary(HevcDeblockingState state, HevcPlane plane, int x, int y)
+            => state.IsVerticalBoundary(plane, x, y);
+
+        /// <inheritdoc/>
+        public static void FilterLuma(
+            HevcPictureBuffer picture,
+            HevcPlane plane,
+            int x,
+            int y,
+            int beta,
+            int tc,
+            bool partPNoFilter,
+            bool partQNoFilter,
+            int bitDepth)
+            => HevcDeblockingFilter.FilterVerticalLuma(picture, plane, x, y, beta, tc, partPNoFilter, partQNoFilter, bitDepth);
+
+        /// <inheritdoc/>
+        public static void FilterChroma(
+            HevcPictureBuffer picture,
+            HevcPlane plane,
+            int x,
+            int y,
+            int tc,
+            bool partPNoFilter,
+            bool partQNoFilter,
+            int bitDepth,
+            int count)
+            => HevcDeblockingFilter.FilterVerticalChroma(picture, plane, x, y, tc, partPNoFilter, partQNoFilter, bitDepth, count);
+    }
+
+    /// <summary>
+    /// Selects horizontal boundary lookup and filtering.
+    /// </summary>
+    private readonly struct HorizontalDeblockingDirection : IDeblockingDirection
+    {
+        /// <inheritdoc/>
+        public static bool IsVertical => false;
+
+        /// <inheritdoc/>
+        public static bool IsBoundary(HevcDeblockingState state, HevcPlane plane, int x, int y)
+            => state.IsHorizontalBoundary(plane, x, y);
+
+        /// <inheritdoc/>
+        public static void FilterLuma(
+            HevcPictureBuffer picture,
+            HevcPlane plane,
+            int x,
+            int y,
+            int beta,
+            int tc,
+            bool partPNoFilter,
+            bool partQNoFilter,
+            int bitDepth)
+            => HevcDeblockingFilter.FilterHorizontalLuma(picture, plane, x, y, beta, tc, partPNoFilter, partQNoFilter, bitDepth);
+
+        /// <inheritdoc/>
+        public static void FilterChroma(
+            HevcPictureBuffer picture,
+            HevcPlane plane,
+            int x,
+            int y,
+            int tc,
+            bool partPNoFilter,
+            bool partQNoFilter,
+            int bitDepth,
+            int count)
+            => HevcDeblockingFilter.FilterHorizontalChroma(picture, plane, x, y, tc, partPNoFilter, partQNoFilter, bitDepth, count);
+    }
+}

src/ImageSharp/Formats/Heif/Hevc/HevcPictureDecoder.Prediction.cs

@@ -0,0 +1,216 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <content>
+/// Implements intra prediction, reconstructed-plane writes, and PCM sample reconstruction.
+/// </content>
+internal sealed partial class HevcPictureDecoder
+{
+    /// <summary>
+    /// Reconstructs one packed intra-prediction block in caller-owned scratch.
+    /// </summary>
+    /// <param name="plane">The reconstructed component plane.</param>
+    /// <param name="x">The prediction-block left coordinate in component samples.</param>
+    /// <param name="y">The prediction-block top coordinate in component samples.</param>
+    /// <param name="log2Size">The base-two logarithm of the square prediction-block side.</param>
+    /// <param name="regionId">The current independent-slice and tile prediction region.</param>
+    /// <param name="colorPlaneIndex">The selected separate-color plane, or zero for combined coding.</param>
+    /// <returns>The packed predicted samples.</returns>
+    private Span<ushort> PredictComponentBlock(HevcPlane plane, int x, int y, int log2Size, int regionId, int colorPlaneIndex)
+    {
+        int size = 1 << log2Size;
+        int sampleCount = size * size;
+        int referenceLength = (size * 2) + 1;
+        Span<ushort> scratch = this.predictionScratch.Memory.Span;
+        Span<ushort> prediction = scratch[..sampleCount];
+        Span<ushort> top = scratch.Slice(MaximumTransformSampleCount, MaximumReferenceLength);
+        Span<ushort> left = scratch.Slice(MaximumTransformSampleCount + MaximumReferenceLength, MaximumReferenceLength);
+        Span<ushort> filteredTop = scratch.Slice(MaximumTransformSampleCount + (MaximumReferenceLength * 2), MaximumReferenceLength);
+        Span<ushort> filteredLeft = scratch.Slice(MaximumTransformSampleCount + (MaximumReferenceLength * 3), MaximumReferenceLength);
+        int referenceScratchOffset = MaximumTransformSampleCount + (MaximumReferenceLength * 4);
+        int unitWidth = this.reconstructionState.GetUnitWidth(plane);
+        int unitHeight = this.reconstructionState.GetUnitHeight(plane);
+        int referenceScratchLength = HevcIntraPredictor.GetReferenceScratchLength(log2Size, unitWidth);
+        Span<ushort> referenceScratch = scratch.Slice(referenceScratchOffset, referenceScratchLength);
+        Span<ushort> operationScratch = scratch[(referenceScratchOffset + referenceScratchLength)..];
+        Span<bool> availability = this.availabilityScratch.Memory.Span;
+        int availabilityCount = this.reconstructionState.BuildReferenceAvailability(
+            plane,
+            x,
+            y,
+            log2Size,
+            regionId,
+            availability);
+
+        HevcIntraPredictor.PrepareReferenceSamples(
+            this.Picture,
+            plane,
+            x,
+            y,
+            log2Size,
+            unitWidth,
+            unitHeight,
+            availability[..availabilityCount],
+            top,
+            left,
+            referenceScratch);
+
+        int lumaX = x << this.Picture.GetSubsamplingX(plane);
+        int lumaY = y << this.Picture.GetSubsamplingY(plane);
+        bool useLumaSyntax = plane == HevcPlane.Y || this.sequenceParameterSet.SeparateColorPlaneFlag;
+        int mode = useLumaSyntax
+            ? this.intraPredictionStates[colorPlaneIndex].GetLumaMode(lumaX, lumaY)
+            : this.intraPredictionStates[colorPlaneIndex].GetEffectiveChromaMode(lumaX, lumaY);
+
+        if (!useLumaSyntax && this.sequenceParameterSet.ChromaFormat == 2)
+        {
+            mode = HevcIntraPredictionMode.RemapChroma422(mode);
+        }
+
+        bool filterReferences = HevcIntraPredictor.ShouldFilterReferenceSamples(
+            useLumaSyntax ? HevcPlane.Y : plane,
+            mode,
+            log2Size,
+            this.sequenceParameterSet.ChromaFormat,
+            this.sequenceParameterSet.IntraSmoothingDisabled);
+
+        ReadOnlySpan<ushort> selectedTop = top[..referenceLength];
+        ReadOnlySpan<ushort> selectedLeft = left[..referenceLength];
+        if (filterReferences)
+        {
+            HevcIntraPredictor.FilterReferenceSamples(
+                selectedTop,
+                selectedLeft,
+                filteredTop,
+                filteredLeft,
+                log2Size,
+                this.Picture.GetBitDepth(plane),
+                this.sequenceParameterSet.StrongIntraSmoothingEnabled);
+
+            selectedTop = filteredTop[..referenceLength];
+            selectedLeft = filteredLeft[..referenceLength];
+        }
+
+        HevcIntraPredictor.Predict(
+            selectedTop,
+            selectedLeft,
+            prediction,
+            size,
+            log2Size,
+            mode,
+            this.Picture.GetBitDepth(plane),
+            useLumaSyntax,
+            operationScratch);
+
+        return prediction;
+    }
+
+    /// <summary>
+    /// Copies one packed reconstructed block into the allocator-owned picture plane.
+    /// </summary>
+    /// <param name="source">The packed reconstructed samples.</param>
+    /// <param name="plane">The destination component plane.</param>
+    /// <param name="x">The destination left coordinate.</param>
+    /// <param name="y">The destination top coordinate.</param>
+    /// <param name="size">The square block side.</param>
+    private void CopyPredictionToPicture(ReadOnlySpan<ushort> source, HevcPlane plane, int x, int y, int size)
+    {
+        for (int row = 0; row < size; row++)
+        {
+            source.Slice(row * size, size).CopyTo(this.Picture.GetRowSpan(plane, y + row)[x..]);
+        }
+    }
+
+    /// <summary>
+    /// Reads and writes every raw sample in one PCM coding unit before arithmetic decoding restarts.
+    /// </summary>
+    /// <param name="reader">The suspended entropy-substream reader.</param>
+    /// <param name="x">The coding-unit left luma coordinate.</param>
+    /// <param name="y">The coding-unit top luma coordinate.</param>
+    /// <param name="log2Size">The base-two logarithm of the coding-unit side.</param>
+    /// <param name="regionId">The current independent-slice and tile prediction region.</param>
+    /// <param name="colorPlaneIndex">The selected separate-color plane, or zero for combined coding.</param>
+    private void DecodePcmCodingUnit(
+        ref HevcCabacSyntaxReader reader,
+        int x,
+        int y,
+        int log2Size,
+        int regionId,
+        int colorPlaneIndex)
+    {
+        int size = 1 << log2Size;
+        if (this.sequenceParameterSet.SeparateColorPlaneFlag)
+        {
+            HevcPlane plane = (HevcPlane)colorPlaneIndex;
+            this.DecodePcmPlane(ref reader, plane, x, y, size, size, this.sequenceParameterSet.PcmBitDepthLuma, regionId);
+            return;
+        }
+
+        this.DecodePcmPlane(ref reader, HevcPlane.Y, x, y, size, size, this.sequenceParameterSet.PcmBitDepthLuma, regionId);
+        if (this.sequenceParameterSet.ChromaFormat == 0)
+        {
+            return;
+        }
+
+        int subsamplingX = this.Picture.GetSubsamplingX(HevcPlane.Cb);
+        int subsamplingY = this.Picture.GetSubsamplingY(HevcPlane.Cb);
+        int chromaWidth = size >> subsamplingX;
+        int chromaHeight = size >> subsamplingY;
+        int chromaX = x >> subsamplingX;
+        int chromaY = y >> subsamplingY;
+        this.DecodePcmPlane(
+            ref reader,
+            HevcPlane.Cb,
+            chromaX,
+            chromaY,
+            chromaWidth,
+            chromaHeight,
+            this.sequenceParameterSet.PcmBitDepthChroma,
+            regionId);
+
+        this.DecodePcmPlane(
+            ref reader,
+            HevcPlane.Cr,
+            chromaX,
+            chromaY,
+            chromaWidth,
+            chromaHeight,
+            this.sequenceParameterSet.PcmBitDepthChroma,
+            regionId);
+    }
+
+    /// <summary>
+    /// Reads one rectangular PCM component plane directly into the reconstructed picture.
+    /// </summary>
+    /// <param name="reader">The suspended entropy-substream reader.</param>
+    /// <param name="plane">The destination component plane.</param>
+    /// <param name="x">The destination left coordinate.</param>
+    /// <param name="y">The destination top coordinate.</param>
+    /// <param name="width">The component rectangle width.</param>
+    /// <param name="height">The component rectangle height.</param>
+    /// <param name="bitDepth">The PCM sample precision.</param>
+    /// <param name="regionId">The current independent-slice and tile prediction region.</param>
+    private void DecodePcmPlane(
+        ref HevcCabacSyntaxReader reader,
+        HevcPlane plane,
+        int x,
+        int y,
+        int width,
+        int height,
+        int bitDepth,
+        int regionId)
+    {
+        for (int row = 0; row < height; row++)
+        {
+            Span<ushort> destination = this.Picture.GetRowSpan(plane, y + row).Slice(x, width);
+            for (int column = 0; column < width; column++)
+            {
+                destination[column] = reader.ReadPcmSample(bitDepth);
+            }
+        }
+
+        this.reconstructionState.MarkReconstructed(plane, x, y, width, height, regionId);
+    }
+}

src/ImageSharp/Formats/Heif/Hevc/HevcPictureDecoder.SampleAdaptiveOffset.cs

@@ -0,0 +1,250 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <content>
+/// Implements sample-adaptive-offset syntax decoding and merge resolution.
+/// </content>
+internal sealed partial class HevcPictureDecoder
+{
+    /// <summary>
+    /// Applies the resolved sample-adaptive offsets to every component after deblocking has completed.
+    /// </summary>
+    /// <param name="source">The immutable deblocked picture used to classify every sample.</param>
+    /// <param name="tileLayout">The picture tile mapping used to derive coding-tree-block boundaries.</param>
+    private void ApplySampleAdaptiveOffset(HevcPictureBuffer source, in HevcTileLayout tileLayout)
+    {
+        int codingTreeBlockSize = 1 << this.sequenceParameterSet.CodingTreeBlockLog2;
+        int planeCount = this.sequenceParameterSet.ChromaFormat == 0 ? 1 : 3;
+        for (int planeIndex = 0; planeIndex < planeCount; planeIndex++)
+        {
+            HevcPlane plane = (HevcPlane)planeIndex;
+            HevcPlane regionPlane = this.sequenceParameterSet.SeparateColorPlaneFlag ? plane : HevcPlane.Y;
+            int subsamplingX = this.Picture.GetSubsamplingX(plane);
+            int subsamplingY = this.Picture.GetSubsamplingY(plane);
+            int blockWidth = codingTreeBlockSize >> subsamplingX;
+            int blockHeight = codingTreeBlockSize >> subsamplingY;
+            int planeWidth = this.Picture.GetWidth(plane);
+            int planeHeight = this.Picture.GetHeight(plane);
+            int offsetScaleLog2 = plane == HevcPlane.Y
+                ? this.pictureParameterSet.SampleAdaptiveOffsetScaleLumaLog2
+                : this.pictureParameterSet.SampleAdaptiveOffsetScaleChromaLog2;
+
+            for (int codingTreeBlockY = 0; codingTreeBlockY < tileLayout.Height; codingTreeBlockY++)
+            {
+                for (int codingTreeBlockX = 0; codingTreeBlockX < tileLayout.Width; codingTreeBlockX++)
+                {
+                    int rasterAddress = (codingTreeBlockY * tileLayout.Width) + codingTreeBlockX;
+                    HevcSampleAdaptiveOffsetParameters parameters = this.sampleAdaptiveOffsetState.Get(rasterAddress, plane);
+                    if (parameters.Type == HevcSampleAdaptiveOffsetType.Off)
+                    {
+                        continue;
+                    }
+
+                    HevcLoopFilterBoundaryAvailability availability = this.sampleAdaptiveOffsetState.GetLoopFilterBoundaryAvailability(
+                        rasterAddress,
+                        regionPlane,
+                        tileLayout.Width,
+                        tileLayout.Height,
+                        this.pictureParameterSet.LoopFilterAcrossTilesEnabled);
+
+                    int x = codingTreeBlockX * blockWidth;
+                    int y = codingTreeBlockY * blockHeight;
+                    int width = Math.Min(blockWidth, planeWidth - x);
+                    int height = Math.Min(blockHeight, planeHeight - y);
+
+                    // Every classification reads the immutable post-deblocking picture. Later CTBs can therefore never
+                    // observe offsets already written by an earlier CTB, including across permitted slice and tile boundaries.
+                    HevcSampleAdaptiveOffsetFilter.ApplyBlock(
+                        source,
+                        this.Picture,
+                        plane,
+                        x,
+                        y,
+                        width,
+                        height,
+                        in parameters,
+                        offsetScaleLog2,
+                        availability.Left,
+                        availability.Right,
+                        availability.Above,
+                        availability.Below,
+                        availability.AboveLeft,
+                        availability.AboveRight,
+                        availability.BelowLeft,
+                        availability.BelowRight);
+                }
+            }
+        }
+    }
+
+    /// <summary>
+    /// Decodes and resolves the sample-adaptive-offset parameters for one coding-tree block.
+    /// </summary>
+    /// <param name="reader">The active entropy-substream reader.</param>
+    /// <param name="independentSlice">The independent slice governing component enable flags.</param>
+    /// <param name="rasterAddress">The coding-tree block's raster-scan address.</param>
+    /// <param name="codingTreeBlockX">The horizontal coding-tree-block coordinate.</param>
+    /// <param name="codingTreeBlockY">The vertical coding-tree-block coordinate.</param>
+    /// <param name="regionId">The current independent-slice and tile prediction region.</param>
+    private void DecodeSampleAdaptiveOffset(
+        ref HevcCabacSyntaxReader reader,
+        HevcSliceSegmentHeader independentSlice,
+        int rasterAddress,
+        int codingTreeBlockX,
+        int codingTreeBlockY,
+        int regionId)
+    {
+        HevcPlane regionPlane = this.sequenceParameterSet.SeparateColorPlaneFlag ? (HevcPlane)independentSlice.ColorPlaneId : HevcPlane.Y;
+        bool lumaEnabled = independentSlice.SampleAdaptiveOffsetLumaEnabled == true;
+        bool chromaEnabled = independentSlice.SampleAdaptiveOffsetChromaEnabled == true;
+        if (!lumaEnabled && !chromaEnabled)
+        {
+            this.sampleAdaptiveOffsetState.SetRegion(rasterAddress, regionPlane, regionId);
+            return;
+        }
+
+        int codingTreeBlockWidth = HevcParameterSetSyntax.GetCodingTreeBlockCount(
+            this.sequenceParameterSet.Width,
+            this.sequenceParameterSet.CodingTreeBlockLog2);
+
+        int leftAddress = rasterAddress - 1;
+        bool leftAvailable = codingTreeBlockX > 0 && this.sampleAdaptiveOffsetState.IsInRegion(leftAddress, regionPlane, regionId);
+        bool mergeLeft = leftAvailable && reader.ReadSampleAdaptiveOffsetMerge();
+        int aboveAddress = rasterAddress - codingTreeBlockWidth;
+        bool aboveAvailable = codingTreeBlockY > 0 && this.sampleAdaptiveOffsetState.IsInRegion(aboveAddress, regionPlane, regionId);
+        bool mergeAbove = !mergeLeft && aboveAvailable && reader.ReadSampleAdaptiveOffsetMerge();
+        if (mergeLeft || mergeAbove)
+        {
+            int sourceAddress = mergeLeft ? leftAddress : aboveAddress;
+            this.CopySampleAdaptiveOffsetParameters(sourceAddress, rasterAddress, lumaEnabled, chromaEnabled, independentSlice.ColorPlaneId);
+            this.sampleAdaptiveOffsetState.SetRegion(rasterAddress, regionPlane, regionId);
+            return;
+        }
+
+        if (this.sequenceParameterSet.SeparateColorPlaneFlag)
+        {
+            HevcPlane plane = (HevcPlane)independentSlice.ColorPlaneId;
+            this.sampleAdaptiveOffsetState.Set(rasterAddress, plane, ReadSampleAdaptiveOffsetParameters(ref reader, this.Picture.GetBitDepth(plane), -1));
+        }
+        else
+        {
+            if (lumaEnabled)
+            {
+                this.sampleAdaptiveOffsetState.Set(
+                    rasterAddress,
+                    HevcPlane.Y,
+                    ReadSampleAdaptiveOffsetParameters(ref reader, this.sequenceParameterSet.BitDepthLuma, -1));
+            }
+
+            if (chromaEnabled)
+            {
+                HevcSampleAdaptiveOffsetParameters chromaBlue = ReadSampleAdaptiveOffsetParameters(
+                    ref reader,
+                    this.sequenceParameterSet.BitDepthChroma,
+                    -1);
+
+                this.sampleAdaptiveOffsetState.Set(rasterAddress, HevcPlane.Cb, chromaBlue);
+                this.sampleAdaptiveOffsetState.Set(
+                    rasterAddress,
+                    HevcPlane.Cr,
+                    ReadSampleAdaptiveOffsetParameters(ref reader, this.sequenceParameterSet.BitDepthChroma, (int)chromaBlue.Type));
+            }
+        }
+
+        this.sampleAdaptiveOffsetState.SetRegion(rasterAddress, regionPlane, regionId);
+    }
+
+    /// <summary>
+    /// Copies resolved merge-source parameters for the components enabled by the current slice.
+    /// </summary>
+    /// <param name="sourceAddress">The merge-source coding-tree-block address.</param>
+    /// <param name="destinationAddress">The current coding-tree-block address.</param>
+    /// <param name="lumaEnabled">Whether the current slice enables luma sample-adaptive offset.</param>
+    /// <param name="chromaEnabled">Whether the current slice enables chroma sample-adaptive offset.</param>
+    /// <param name="colorPlaneId">The selected separate-color-plane identifier.</param>
+    private void CopySampleAdaptiveOffsetParameters(
+        int sourceAddress,
+        int destinationAddress,
+        bool lumaEnabled,
+        bool chromaEnabled,
+        byte colorPlaneId)
+    {
+        if (this.sequenceParameterSet.SeparateColorPlaneFlag)
+        {
+            HevcPlane plane = (HevcPlane)colorPlaneId;
+            this.sampleAdaptiveOffsetState.Set(destinationAddress, plane, this.sampleAdaptiveOffsetState.Get(sourceAddress, plane));
+            return;
+        }
+
+        if (lumaEnabled)
+        {
+            this.sampleAdaptiveOffsetState.Set(destinationAddress, HevcPlane.Y, this.sampleAdaptiveOffsetState.Get(sourceAddress, HevcPlane.Y));
+        }
+
+        if (chromaEnabled)
+        {
+            this.sampleAdaptiveOffsetState.Set(destinationAddress, HevcPlane.Cb, this.sampleAdaptiveOffsetState.Get(sourceAddress, HevcPlane.Cb));
+            this.sampleAdaptiveOffsetState.Set(destinationAddress, HevcPlane.Cr, this.sampleAdaptiveOffsetState.Get(sourceAddress, HevcPlane.Cr));
+        }
+    }
+
+    /// <summary>
+    /// Decodes one component's new or disabled sample-adaptive-offset mode.
+    /// </summary>
+    /// <param name="reader">The active entropy-substream reader.</param>
+    /// <param name="bitDepth">The component sample precision.</param>
+    /// <param name="inheritedType">The Cb type inherited by Cr, or negative one when the type is signaled.</param>
+    /// <returns>The resolved component parameters.</returns>
+    private static HevcSampleAdaptiveOffsetParameters ReadSampleAdaptiveOffsetParameters(
+        ref HevcCabacSyntaxReader reader,
+        int bitDepth,
+        int inheritedType)
+    {
+        int type = inheritedType >= 0
+            ? inheritedType == (int)HevcSampleAdaptiveOffsetType.Off ? 0 : inheritedType == (int)HevcSampleAdaptiveOffsetType.Band ? 1 : 2
+            : reader.ReadSampleAdaptiveOffsetType();
+
+        if (type == 0)
+        {
+            return default;
+        }
+
+        int maximumOffset = (1 << (Math.Min(bitDepth, 10) - 5)) - 1;
+        int offset0 = reader.ReadSampleAdaptiveOffsetAbsolute(maximumOffset);
+        int offset1 = reader.ReadSampleAdaptiveOffsetAbsolute(maximumOffset);
+        int offset2 = reader.ReadSampleAdaptiveOffsetAbsolute(maximumOffset);
+        int offset3 = reader.ReadSampleAdaptiveOffsetAbsolute(maximumOffset);
+        if (type == 1)
+        {
+            offset0 = ApplySampleAdaptiveOffsetSign(ref reader, offset0);
+            offset1 = ApplySampleAdaptiveOffsetSign(ref reader, offset1);
+            offset2 = ApplySampleAdaptiveOffsetSign(ref reader, offset2);
+            offset3 = ApplySampleAdaptiveOffsetSign(ref reader, offset3);
+            return new HevcSampleAdaptiveOffsetParameters(
+                HevcSampleAdaptiveOffsetType.Band,
+                reader.ReadSampleAdaptiveOffsetBandPosition(),
+                offset0,
+                offset1,
+                offset2,
+                offset3,
+                0);
+        }
+
+        HevcSampleAdaptiveOffsetType edgeType = inheritedType >= 0
+            ? (HevcSampleAdaptiveOffsetType)inheritedType
+            : (HevcSampleAdaptiveOffsetType)((int)HevcSampleAdaptiveOffsetType.EdgeHorizontal + reader.ReadSampleAdaptiveOffsetEdgeClass());
+
+        return new HevcSampleAdaptiveOffsetParameters(edgeType, 0, offset0, offset1, 0, -offset2, -offset3);
+    }
+
+    /// <summary>
+    /// Applies an explicitly coded sign to a nonzero band-offset magnitude.
+    /// </summary>
+    /// <param name="reader">The active entropy-substream reader.</param>
+    /// <param name="magnitude">The decoded unsigned magnitude.</param>
+    /// <returns>The signed magnitude.</returns>
+    private static int ApplySampleAdaptiveOffsetSign(ref HevcCabacSyntaxReader reader, int magnitude)
+        => magnitude != 0 && reader.ReadSampleAdaptiveOffsetSign() ? -magnitude : magnitude;
+}

src/ImageSharp/Formats/Heif/Hevc/HevcPictureDecoder.TransformTree.cs

@@ -0,0 +1,562 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Numerics;
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <content>
+/// Implements transform-tree syntax, coefficient reconstruction, and intra sample reconstruction.
+/// </content>
+internal sealed partial class HevcPictureDecoder
+{
+    /// <summary>
+    /// Decodes and reconstructs one transform-tree node.
+    /// </summary>
+    /// <param name="reader">The active entropy-substream reader.</param>
+    /// <param name="geometry">The luma and component rectangles at this transform depth.</param>
+    /// <param name="transformDepth">The transform depth relative to the coding-unit root.</param>
+    /// <param name="minimumTransformLog2">The smallest luma transform permitted in the coding unit.</param>
+    /// <param name="usesNxNPartitions">Whether the coding unit has four luma prediction partitions.</param>
+    /// <param name="transquantBypass">Whether the coding unit bypasses inverse quantization and transform.</param>
+    /// <param name="regionId">The current independent-slice and tile prediction region.</param>
+    /// <param name="colorPlaneIndex">The selected separate-color plane, or zero for combined coding.</param>
+    /// <param name="parentChromaBlueFlags">The blue-difference coded-block flags inherited from the parent.</param>
+    /// <param name="parentChromaRedFlags">The red-difference coded-block flags inherited from the parent.</param>
+    private void DecodeTransformTree(
+        ref HevcCabacSyntaxReader reader,
+        in HevcTransformUnitGeometry geometry,
+        int transformDepth,
+        int minimumTransformLog2,
+        bool usesNxNPartitions,
+        bool transquantBypass,
+        int regionId,
+        int colorPlaneIndex,
+        HevcCodedBlockFlags parentChromaBlueFlags,
+        HevcCodedBlockFlags parentChromaRedFlags)
+    {
+        int log2Size = geometry.Log2LumaSize;
+        HevcTransformComponentGeometry primaryGeometry = geometry.Primary;
+        HevcTransformComponentGeometry chromaBlueGeometry = geometry.ChromaBlue;
+        HevcTransformComponentGeometry chromaRedGeometry = geometry.ChromaRed;
+        bool split;
+        if (usesNxNPartitions && transformDepth == 0)
+        {
+            split = true;
+        }
+        else if (log2Size > this.sequenceParameterSet.MaxTransformBlockLog2)
+        {
+            split = true;
+        }
+        else if (log2Size == this.sequenceParameterSet.MinTransformBlockLog2 || log2Size == minimumTransformLog2)
+        {
+            split = false;
+        }
+        else
+        {
+            split = reader.ReadTransformSubdivision(log2Size);
+        }
+
+        HevcCodedBlockFlags chromaBlueFlags = parentChromaBlueFlags;
+        HevcCodedBlockFlags chromaRedFlags = parentChromaRedFlags;
+        if (geometry.HasCombinedChroma)
+        {
+            chromaBlueFlags = DecodeChromaCodedBlockFlags(
+                ref reader,
+                in chromaBlueGeometry,
+                transformDepth,
+                split,
+                parentChromaBlueFlags);
+
+            chromaRedFlags = DecodeChromaCodedBlockFlags(
+                ref reader,
+                in chromaRedGeometry,
+                transformDepth,
+                split,
+                parentChromaRedFlags);
+        }
+
+        if (split)
+        {
+            for (int child = 0; child < 4; child++)
+            {
+                HevcTransformUnitGeometry childGeometry = geometry.CreateChild(child);
+                this.DecodeTransformTree(
+                    ref reader,
+                    in childGeometry,
+                    transformDepth + 1,
+                    minimumTransformLog2,
+                    usesNxNPartitions,
+                    transquantBypass,
+                    regionId,
+                    colorPlaneIndex,
+                    chromaBlueFlags,
+                    chromaRedFlags);
+            }
+
+            return;
+        }
+
+        this.deblockingState.MarkBlock(
+            geometry.PrimaryPlane,
+            primaryGeometry.X,
+            primaryGeometry.Y,
+            primaryGeometry.Width,
+            primaryGeometry.Height);
+
+        HevcCodedBlockFlags primaryFlags = new(reader.ReadTransformCodedBlockFlag(false, transformDepth == 0 ? 1 : 0));
+        bool hasCodedResidual = primaryFlags.Any || chromaBlueFlags.Any || chromaRedFlags.Any;
+        if (hasCodedResidual && this.quantizationParameterDeltaPending)
+        {
+            this.ApplyQuantizationParameterDelta(reader.ReadDeltaQuantizationParameter());
+            this.quantizationParameterDeltaPending = false;
+        }
+
+        if ((chromaBlueFlags.Any || chromaRedFlags.Any)
+            && this.chromaQuantizationAdjustmentPending
+            && !transquantBypass)
+        {
+            this.currentChromaQuantizationAdjustment = reader.ReadChromaQuantizationAdjustment(
+                this.pictureParameterSet.ChromaQuantizationParameterOffsetsCb.Count);
+
+            this.chromaQuantizationAdjustmentPending = false;
+        }
+
+        HevcQuantizationParameters quantizationParameters = this.CreateQuantizationParameters();
+        Span<int> lumaResidual = this.integerScratch.Memory.Span.Slice(MaximumTransformSampleCount * 3, MaximumTransformSampleCount);
+        lumaResidual.Clear();
+        this.DecodeComponentSections(
+            ref reader,
+            geometry.PrimaryPlane,
+            in primaryGeometry,
+            primaryFlags,
+            transquantBypass,
+            regionId,
+            colorPlaneIndex,
+            in quantizationParameters,
+            lumaResidual,
+            true,
+            0,
+            in primaryGeometry);
+
+        if (!geometry.HasCombinedChroma)
+        {
+            return;
+        }
+
+        int chromaMode = this.intraPredictionStates[colorPlaneIndex].GetChromaMode(geometry.Primary.X, geometry.Primary.Y);
+        int chromaBlueAlpha = 0;
+        bool canPredictAcrossComponents = this.pictureParameterSet.CrossComponentPredictionEnabled
+            && primaryFlags.Any
+            && chromaMode == 36
+            && chromaBlueGeometry.Width == chromaBlueGeometry.Height;
+
+        if (canPredictAcrossComponents)
+        {
+            chromaBlueAlpha = reader.ReadCrossComponentPredictionScale(0);
+        }
+
+        this.DecodeComponentSections(
+            ref reader,
+            HevcPlane.Cb,
+            in chromaBlueGeometry,
+            chromaBlueFlags,
+            transquantBypass,
+            regionId,
+            colorPlaneIndex,
+            in quantizationParameters,
+            lumaResidual,
+            false,
+            chromaBlueAlpha,
+            in primaryGeometry);
+
+        int chromaRedAlpha = 0;
+        if (canPredictAcrossComponents)
+        {
+            // The Cr scale follows the complete Cb residual syntax. Reading both scales together changes every
+            // subsequent CABAC decision whenever Cb carries coefficients.
+            chromaRedAlpha = reader.ReadCrossComponentPredictionScale(1);
+        }
+
+        this.DecodeComponentSections(
+            ref reader,
+            HevcPlane.Cr,
+            in chromaRedGeometry,
+            chromaRedFlags,
+            transquantBypass,
+            regionId,
+            colorPlaneIndex,
+            in quantizationParameters,
+            lumaResidual,
+            false,
+            chromaRedAlpha,
+            in primaryGeometry);
+    }
+
+    /// <summary>
+    /// Decodes chroma coded-block flags at the highest transform level that owns the component rectangle.
+    /// </summary>
+    /// <param name="reader">The active entropy-substream reader.</param>
+    /// <param name="geometry">The current chroma component rectangle.</param>
+    /// <param name="transformDepth">The luma transform depth.</param>
+    /// <param name="lumaSplit">Whether the current luma transform node subdivides.</param>
+    /// <param name="parentFlags">The coded-block flags inherited from the parent transform node.</param>
+    /// <returns>The flags governing the current component rectangle.</returns>
+    private static HevcCodedBlockFlags DecodeChromaCodedBlockFlags(
+        ref HevcCabacSyntaxReader reader,
+        in HevcTransformComponentGeometry geometry,
+        int transformDepth,
+        bool lumaSplit,
+        HevcCodedBlockFlags parentFlags)
+    {
+        if (!geometry.Process)
+        {
+            return parentFlags;
+        }
+
+        bool shouldDecode = transformDepth == 0 || (geometry.ProcessesAllQuadrants && parentFlags.Any);
+        if (!shouldDecode)
+        {
+            return parentFlags;
+        }
+
+        int context = transformDepth;
+        bool canQuadSplit = geometry.Width >= 8 && geometry.Height >= 8;
+        if (geometry.Width != geometry.Height && (!lumaSplit || !canQuadSplit))
+        {
+            bool first = reader.ReadTransformCodedBlockFlag(true, context);
+            bool second = reader.ReadTransformCodedBlockFlag(true, context);
+            return new HevcCodedBlockFlags(first, second);
+        }
+
+        return new HevcCodedBlockFlags(reader.ReadTransformCodedBlockFlag(true, context));
+    }
+
+    /// <summary>
+    /// Decodes one square component block or the two square sub-blocks of a rectangular 4:2:2 transform section.
+    /// </summary>
+    /// <param name="reader">The active entropy-substream reader.</param>
+    /// <param name="plane">The reconstructed component plane.</param>
+    /// <param name="geometry">The component rectangle.</param>
+    /// <param name="codedBlockFlags">The component coded-block flags.</param>
+    /// <param name="transquantBypass">Whether the coding unit bypasses inverse quantization and transform.</param>
+    /// <param name="regionId">The current independent-slice and tile prediction region.</param>
+    /// <param name="colorPlaneIndex">The selected separate-color plane, or zero for combined coding.</param>
+    /// <param name="quantizationParameters">The effective component quantization parameters.</param>
+    /// <param name="lumaResidual">The current luma residual retained for cross-component prediction.</param>
+    /// <param name="retainResidual">Whether reconstructed residuals are copied to <paramref name="lumaResidual"/>.</param>
+    /// <param name="crossComponentAlpha">The signed inverse cross-component prediction scale.</param>
+    /// <param name="lumaGeometry">The luma transform rectangle governing cross-component residual addressing.</param>
+    private void DecodeComponentSections(
+        ref HevcCabacSyntaxReader reader,
+        HevcPlane plane,
+        in HevcTransformComponentGeometry geometry,
+        HevcCodedBlockFlags codedBlockFlags,
+        bool transquantBypass,
+        int regionId,
+        int colorPlaneIndex,
+        in HevcQuantizationParameters quantizationParameters,
+        Span<int> lumaResidual,
+        bool retainResidual,
+        int crossComponentAlpha,
+        in HevcTransformComponentGeometry lumaGeometry)
+    {
+        if (!geometry.Process)
+        {
+            return;
+        }
+
+        if (geometry.Width == geometry.Height)
+        {
+            this.DecodeComponentBlock(
+                ref reader,
+                plane,
+                geometry.X,
+                geometry.Y,
+                geometry.Width,
+                codedBlockFlags.First,
+                transquantBypass,
+                regionId,
+                colorPlaneIndex,
+                in quantizationParameters,
+                lumaResidual,
+                retainResidual,
+                crossComponentAlpha,
+                this.GetLumaResidualOffset(plane, geometry.X, geometry.Y, in lumaGeometry),
+                lumaGeometry.Width);
+
+            return;
+        }
+
+        int size = Math.Min(geometry.Width, geometry.Height);
+        int secondX = geometry.Width > geometry.Height ? geometry.X + size : geometry.X;
+        int secondY = geometry.Height > geometry.Width ? geometry.Y + size : geometry.Y;
+        this.DecodeComponentBlock(
+            ref reader,
+            plane,
+            geometry.X,
+            geometry.Y,
+            size,
+            codedBlockFlags.First,
+            transquantBypass,
+            regionId,
+            colorPlaneIndex,
+            in quantizationParameters,
+            lumaResidual,
+            retainResidual,
+            crossComponentAlpha,
+            this.GetLumaResidualOffset(plane, geometry.X, geometry.Y, in lumaGeometry),
+            lumaGeometry.Width);
+
+        this.DecodeComponentBlock(
+            ref reader,
+            plane,
+            secondX,
+            secondY,
+            size,
+            codedBlockFlags.Second,
+            transquantBypass,
+            regionId,
+            colorPlaneIndex,
+            in quantizationParameters,
+            lumaResidual,
+            retainResidual,
+            crossComponentAlpha,
+            this.GetLumaResidualOffset(plane, secondX, secondY, in lumaGeometry),
+            lumaGeometry.Width);
+    }
+
+    /// <summary>
+    /// Decodes, predicts, and reconstructs one square transform block.
+    /// </summary>
+    /// <param name="reader">The active entropy-substream reader.</param>
+    /// <param name="plane">The reconstructed component plane.</param>
+    /// <param name="x">The block left coordinate in component samples.</param>
+    /// <param name="y">The block top coordinate in component samples.</param>
+    /// <param name="size">The square transform-block side.</param>
+    /// <param name="codedBlockFlag">Whether coefficient syntax is present.</param>
+    /// <param name="transquantBypass">Whether the coding unit bypasses inverse quantization and transform.</param>
+    /// <param name="regionId">The current independent-slice and tile prediction region.</param>
+    /// <param name="colorPlaneIndex">The selected separate-color plane, or zero for combined coding.</param>
+    /// <param name="quantizationParameters">The effective component quantization parameters.</param>
+    /// <param name="lumaResidual">The current luma residual retained for cross-component prediction.</param>
+    /// <param name="retainResidual">Whether reconstructed residuals are copied to <paramref name="lumaResidual"/>.</param>
+    /// <param name="crossComponentAlpha">The signed inverse cross-component prediction scale.</param>
+    /// <param name="lumaResidualOffset">The first colocated sample in the retained luma residual.</param>
+    /// <param name="lumaResidualStride">The retained luma residual row stride.</param>
+    private void DecodeComponentBlock(
+        ref HevcCabacSyntaxReader reader,
+        HevcPlane plane,
+        int x,
+        int y,
+        int size,
+        bool codedBlockFlag,
+        bool transquantBypass,
+        int regionId,
+        int colorPlaneIndex,
+        in HevcQuantizationParameters quantizationParameters,
+        Span<int> lumaResidual,
+        bool retainResidual,
+        int crossComponentAlpha,
+        int lumaResidualOffset,
+        int lumaResidualStride)
+    {
+        int log2Size = BitOperations.Log2((uint)size);
+        int sampleCount = size * size;
+        Span<int> integerScratch = this.integerScratch.Memory.Span;
+        Span<int> quantized = integerScratch[..MaximumTransformSampleCount];
+        Span<int> dequantized = integerScratch.Slice(MaximumTransformSampleCount, MaximumTransformSampleCount);
+        Span<int> residual = integerScratch.Slice(MaximumTransformSampleCount * 2, MaximumTransformSampleCount);
+        Span<int> transformScratch = integerScratch.Slice(MaximumTransformSampleCount * 4, MaximumTransformSampleCount * 2);
+        Span<ushort> prediction = this.PredictComponentBlock(plane, x, y, log2Size, regionId, colorPlaneIndex);
+        residual[..sampleCount].Clear();
+        bool useLumaSyntax = this.sequenceParameterSet.SeparateColorPlaneFlag;
+        HevcPlane codingPlane = useLumaSyntax ? HevcPlane.Y : plane;
+        int lumaX = x << this.Picture.GetSubsamplingX(plane);
+        int lumaY = y << this.Picture.GetSubsamplingY(plane);
+        int codingPredictionMode = plane == HevcPlane.Y || useLumaSyntax
+            ? this.intraPredictionStates[colorPlaneIndex].GetLumaMode(lumaX, lumaY)
+            : this.intraPredictionStates[colorPlaneIndex].GetEffectiveChromaMode(lumaX, lumaY);
+
+        int predictionMode = codingPredictionMode;
+        if (plane != HevcPlane.Y && !useLumaSyntax && this.sequenceParameterSet.ChromaFormat == 2)
+        {
+            predictionMode = HevcIntraPredictionMode.RemapChroma422(predictionMode);
+        }
+
+        bool transformSkip = codedBlockFlag
+            && !transquantBypass
+            && this.pictureParameterSet.TransformSkipEnabled
+            && log2Size <= this.pictureParameterSet.MaxTransformSkipBlockLog2
+            && reader.ReadTransformSkip(codingPlane != HevcPlane.Y);
+
+        HevcResidualDpcmMode residualDpcmMode = this.sequenceParameterSet.ImplicitResidualDpcmEnabled && (transformSkip || transquantBypass)
+            ? HevcResidualReconstructor.GetImplicitResidualDpcmMode(predictionMode, false)
+            : HevcResidualDpcmMode.None;
+
+        if (codedBlockFlag)
+        {
+            HevcCoefficientCodingParameters codingParameters = HevcCoefficientCodingParameters.Create(
+                this.pictureParameterSet,
+                size,
+                size,
+                plane,
+                true,
+                codingPredictionMode,
+                transformSkip,
+                transquantBypass,
+                residualDpcmMode,
+                useLumaSyntax);
+
+            this.coefficientDecoder.Decode(ref reader, quantized, in codingParameters);
+            bool rotate = HevcResidualReconstructor.IsNonTransformedResidualRotated(
+                this.sequenceParameterSet.TransformSkipRotationEnabled,
+                true,
+                size);
+
+            if (transquantBypass)
+            {
+                HevcResidualReconstructor.CopyBypassed(quantized[..sampleCount], residual, rotate);
+            }
+            else
+            {
+                int bitDepth = this.Picture.GetBitDepth(plane);
+                int maxTransformDynamicRange = this.sequenceParameterSet.GetMaxTransformDynamicRange(codingPlane);
+                int quantizationParameter = useLumaSyntax
+                    ? quantizationParameters.Luma
+                    : quantizationParameters.Get(plane);
+
+                HevcInverseQuantizer.Dequantize(
+                    quantized,
+                    dequantized,
+                    log2Size,
+                    bitDepth,
+                    maxTransformDynamicRange,
+                    quantizationParameter,
+                    this.sequenceParameterSet.ScalingListEnabled,
+                    this.pictureParameterSet.ScalingList,
+                    codingPlane,
+                    true,
+                    transformSkip,
+                    this.sequenceParameterSet.ExtendedPrecisionProcessingEnabled);
+
+                if (transformSkip)
+                {
+                    HevcResidualReconstructor.ApplyTransformSkip(
+                        dequantized,
+                        residual,
+                        size,
+                        size,
+                        bitDepth,
+                        maxTransformDynamicRange,
+                        log2Size,
+                        this.sequenceParameterSet.ExtendedPrecisionProcessingEnabled,
+                        rotate);
+                }
+                else
+                {
+                    HevcInverseTransformer.Transform(
+                        dequantized,
+                        residual,
+                        log2Size,
+                        log2Size,
+                        bitDepth,
+                        maxTransformDynamicRange,
+                        codingPlane == HevcPlane.Y && log2Size == 2,
+                        transformScratch);
+                }
+            }
+
+            HevcResidualReconstructor.ApplyResidualDpcm(residual, size, size, residualDpcmMode);
+        }
+
+        if (crossComponentAlpha != 0)
+        {
+            for (int row = 0; row < size; row++)
+            {
+                HevcResidualReconstructor.ApplyCrossComponentPrediction(
+                    lumaResidual.Slice(lumaResidualOffset + (row * lumaResidualStride), size),
+                    residual.Slice(row * size, size),
+                    size,
+                    crossComponentAlpha,
+                    this.sequenceParameterSet.BitDepthLuma - this.sequenceParameterSet.BitDepthChroma);
+            }
+        }
+
+        if (retainResidual)
+        {
+            for (int row = 0; row < size; row++)
+            {
+                residual.Slice(row * size, size).CopyTo(lumaResidual.Slice(lumaResidualOffset + (row * lumaResidualStride), size));
+            }
+        }
+
+        HevcInverseTransformer.AddResidual(
+            residual,
+            prediction,
+            size,
+            size,
+            size,
+            this.Picture.GetBitDepth(plane));
+
+        this.CopyPredictionToPicture(prediction, plane, x, y, size);
+        this.reconstructionState.MarkReconstructed(plane, x, y, size, size, regionId);
+    }
+
+    /// <summary>
+    /// Gets the packed luma-residual offset colocated with one component block.
+    /// </summary>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The component block left coordinate.</param>
+    /// <param name="y">The component block top coordinate.</param>
+    /// <param name="lumaGeometry">The governing luma transform rectangle.</param>
+    /// <returns>The zero-based packed luma-residual offset.</returns>
+    private int GetLumaResidualOffset(HevcPlane plane, int x, int y, in HevcTransformComponentGeometry lumaGeometry)
+    {
+        int lumaX = x << this.Picture.GetSubsamplingX(plane);
+        int lumaY = y << this.Picture.GetSubsamplingY(plane);
+        return ((lumaY - lumaGeometry.Y) * lumaGeometry.Width) + lumaX - lumaGeometry.X;
+    }
+
+    /// <summary>
+    /// Applies the signed coding-unit luma quantization delta with bit-depth-dependent modular wrapping.
+    /// </summary>
+    /// <param name="delta">The decoded signed delta.</param>
+    private void ApplyQuantizationParameterDelta(int delta)
+    {
+        int bitDepthOffset = 6 * (this.sequenceParameterSet.BitDepthLuma - 8);
+        int modulus = 52 + bitDepthOffset;
+        int value = this.currentQuantizationParameter + delta + bitDepthOffset;
+        value %= modulus;
+        if (value < 0)
+        {
+            value += modulus;
+        }
+
+        this.currentQuantizationParameter = value - bitDepthOffset;
+    }
+
+    /// <summary>
+    /// Creates the component quantization parameters selected by picture, slice, and coding-unit offsets.
+    /// </summary>
+    /// <returns>The effective luma, Cb, and Cr quantization parameters.</returns>
+    private HevcQuantizationParameters CreateQuantizationParameters()
+    {
+        int cbOffset = this.pictureParameterSet.ChromaCbQuantizationParameterOffset + this.currentSliceChromaBlueQuantizationOffset;
+        int crOffset = this.pictureParameterSet.ChromaCrQuantizationParameterOffset + this.currentSliceChromaRedQuantizationOffset;
+        if (this.currentChromaQuantizationAdjustment > 0)
+        {
+            int adjustmentIndex = this.currentChromaQuantizationAdjustment - 1;
+            cbOffset += this.pictureParameterSet.ChromaQuantizationParameterOffsetsCb[adjustmentIndex];
+            crOffset += this.pictureParameterSet.ChromaQuantizationParameterOffsetsCr[adjustmentIndex];
+        }
+
+        return new HevcQuantizationParameters(
+            this.currentQuantizationParameter,
+            this.sequenceParameterSet.BitDepthLuma,
+            this.sequenceParameterSet.BitDepthChroma,
+            this.sequenceParameterSet.ChromaFormat,
+            cbOffset,
+            crOffset);
+    }
+}

src/ImageSharp/Formats/Heif/Hevc/HevcPictureDecoder.Traversal.cs

@@ -0,0 +1,364 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <content>
+/// Implements slice, coding-tree, and coding-unit traversal.
+/// </content>
+internal sealed partial class HevcPictureDecoder
+{
+    /// <summary>
+    /// Decodes one ordered slice segment and returns the next tile-scan coding-tree-block address.
+    /// </summary>
+    /// <param name="slice">The current independent or dependent slice segment.</param>
+    /// <param name="independentSlice">The independent header governing inherited slice fields.</param>
+    /// <param name="independentSliceIndex">The one-based independent-slice index within the selected color plane.</param>
+    /// <param name="tileLayout">The picture tile mapping.</param>
+    /// <param name="startAddressInTileScan">The first coding-tree block in tile-scan order.</param>
+    /// <param name="independentSliceStartAddressInTileScan">The governing independent slice's first coding-tree block in tile-scan order.</param>
+    /// <returns>The tile-scan address immediately following the decoded segment.</returns>
+    private int DecodeSliceSegment(
+        HevcSliceSegmentHeader slice,
+        HevcSliceSegmentHeader independentSlice,
+        int independentSliceIndex,
+        in HevcTileLayout tileLayout,
+        int startAddressInTileScan,
+        int independentSliceStartAddressInTileScan)
+    {
+        int sliceQuantizationParameter = independentSlice.QuantizationParameter!.Value;
+        int colorPlaneIndex = this.sequenceParameterSet.SeparateColorPlaneFlag ? independentSlice.ColorPlaneId : 0;
+        this.lastCodedQuantizationParameter = sliceQuantizationParameter;
+        this.currentQuantizationParameter = sliceQuantizationParameter;
+        this.currentChromaQuantizationAdjustment = 0;
+        this.currentSliceChromaBlueQuantizationOffset = independentSlice.ChromaCbQuantizationParameterOffset;
+        this.currentSliceChromaRedQuantizationOffset = independentSlice.ChromaCrQuantizationParameterOffset;
+        this.quantizationParameterDeltaPending = this.pictureParameterSet.CodingUnitQuantizationParameterDeltaEnabled;
+        this.chromaQuantizationAdjustmentPending = independentSlice.ChromaQuantizationParameterOffsetListEnabled == true;
+        int substreamIndex = 0;
+        HevcCabacSyntaxReader reader = new(slice.GetEntropySubstream(substreamIndex).Span, sliceQuantizationParameter);
+        this.coefficientDecoder.ResetRiceAdaptation();
+
+        int contextOffset = colorPlaneIndex * HevcCabacContexts.ContextCount;
+        int riceOffset = colorPlaneIndex * 4;
+        if (slice.DependentSliceSegment && this.hasSliceSegmentContexts[colorPlaneIndex])
+        {
+            reader.CopyContextsFrom(this.sliceSegmentContexts.AsSpan(contextOffset, HevcCabacContexts.ContextCount));
+            this.coefficientDecoder.CopyRiceAdaptationFrom(this.sliceSegmentRiceAdaptation.AsSpan(riceOffset, 4));
+        }
+
+        int codingTreeBlockSize = 1 << this.sequenceParameterSet.CodingTreeBlockLog2;
+        int tileScanAddress = startAddressInTileScan;
+        bool firstCodingTreeBlock = true;
+        bool wavefrontStateAvailable = false;
+        while (tileScanAddress < tileLayout.Width * tileLayout.Height)
+        {
+            int rasterAddress = tileLayout.GetRasterAddress(tileScanAddress);
+            tileLayout.GetTilePosition(
+                rasterAddress,
+                out int tileIndex,
+                out int columnInTile,
+                out int rowInTile,
+                out int tileWidth,
+                out int tileHeight);
+
+            bool startsTile = columnInTile == 0 && rowInTile == 0;
+            bool startsWavefrontRow = this.pictureParameterSet.EntropyCodingSynchronizationEnabled && columnInTile == 0 && rowInTile > 0;
+            if (!firstCodingTreeBlock && (startsTile || startsWavefrontRow))
+            {
+                if (!reader.ReadTerminate())
+                {
+                    throw new InvalidImageContentException("The HEVC entropy substream does not terminate at its tile or wavefront boundary.");
+                }
+
+                reader.ValidateTerminationAlignment();
+                substreamIndex++;
+                if (substreamIndex >= slice.EntropySubstreamCount)
+                {
+                    throw new InvalidImageContentException("The HEVC slice segment has too few entropy entry points.");
+                }
+
+                reader = new HevcCabacSyntaxReader(slice.GetEntropySubstream(substreamIndex).Span, sliceQuantizationParameter);
+                this.coefficientDecoder.ResetRiceAdaptation();
+                this.lastCodedQuantizationParameter = sliceQuantizationParameter;
+                if (startsWavefrontRow && tileWidth > 1 && wavefrontStateAvailable)
+                {
+                    reader.CopyContextsFrom(this.wavefrontContexts);
+                    this.coefficientDecoder.CopyRiceAdaptationFrom(this.wavefrontRiceAdaptation[..4]);
+                }
+            }
+
+            int ctbX = rasterAddress % tileLayout.Width;
+            int ctbY = rasterAddress / tileLayout.Width;
+            int x = ctbX * codingTreeBlockSize;
+            int y = ctbY * codingTreeBlockSize;
+            int regionId = ((independentSliceIndex - 1) * tileLayout.TileCount) + tileIndex + 1;
+            HevcPlane regionPlane = this.sequenceParameterSet.SeparateColorPlaneFlag ? (HevcPlane)colorPlaneIndex : HevcPlane.Y;
+            HevcLoopFilterRegion loopFilterRegion = new(
+                independentSliceStartAddressInTileScan,
+                tileIndex,
+                independentSlice.LoopFilterAcrossSlicesEnabled == true,
+                independentSlice.DeblockingFilterDisabled == true,
+                independentSlice.DeblockingFilterBetaOffsetDiv2,
+                independentSlice.DeblockingFilterTcOffsetDiv2);
+
+            this.sampleAdaptiveOffsetState.SetLoopFilterRegion(rasterAddress, regionPlane, loopFilterRegion);
+            this.DecodeSampleAdaptiveOffset(ref reader, independentSlice, rasterAddress, ctbX, ctbY, regionId);
+            bool endOfSliceSegment = this.DecodeCodingTree(
+                ref reader,
+                x,
+                y,
+                this.sequenceParameterSet.CodingTreeBlockLog2,
+                0,
+                regionId,
+                colorPlaneIndex);
+
+            // Wavefront synchronization copies probability and persistent Rice state after the second CTB of each
+            // row. The next row starts with those contexts but a newly initialized arithmetic register.
+            if (this.pictureParameterSet.EntropyCodingSynchronizationEnabled && columnInTile == 1)
+            {
+                reader.CopyContextsTo(this.wavefrontContexts);
+                this.coefficientDecoder.CopyRiceAdaptationTo(this.wavefrontRiceAdaptation[..4]);
+                wavefrontStateAvailable = true;
+            }
+
+            tileScanAddress++;
+            firstCodingTreeBlock = false;
+            if (endOfSliceSegment)
+            {
+                reader.ValidateTerminationAlignment();
+                if (substreamIndex + 1 != slice.EntropySubstreamCount)
+                {
+                    throw new InvalidImageContentException("The HEVC slice segment has unused entropy entry points.");
+                }
+
+                reader.CopyContextsTo(this.sliceSegmentContexts.AsSpan(contextOffset, HevcCabacContexts.ContextCount));
+                this.coefficientDecoder.CopyRiceAdaptationTo(this.sliceSegmentRiceAdaptation.AsSpan(riceOffset, 4));
+                this.hasSliceSegmentContexts[colorPlaneIndex] = true;
+                return tileScanAddress;
+            }
+
+            bool atTileEnd = columnInTile == tileWidth - 1 && rowInTile == tileHeight - 1;
+            bool atWavefrontRowEnd = this.pictureParameterSet.EntropyCodingSynchronizationEnabled && columnInTile == tileWidth - 1;
+            if (atTileEnd || atWavefrontRowEnd)
+            {
+                // A non-final tile or wavefront row has a second terminating bin after the coding-unit end flag.
+                // It is consumed when the following loop iteration opens the next bounded entropy substream.
+                continue;
+            }
+        }
+
+        throw new InvalidImageContentException("The HEVC slice segment reaches the picture boundary without termination.");
+    }
+
+    /// <summary>
+    /// Decodes one coding-tree node in depth-first Z order.
+    /// </summary>
+    /// <param name="reader">The active entropy-substream reader.</param>
+    /// <param name="x">The coding-node left luma coordinate.</param>
+    /// <param name="y">The coding-node top luma coordinate.</param>
+    /// <param name="log2Size">The base-two logarithm of the coding-node side.</param>
+    /// <param name="depth">The coding-tree depth below the coding-tree-block root.</param>
+    /// <param name="regionId">The current independent-slice and tile prediction region.</param>
+    /// <param name="colorPlaneIndex">The selected separate-color plane, or zero for combined coding.</param>
+    /// <returns><see langword="true"/> when the current leaf terminates the slice segment.</returns>
+    private bool DecodeCodingTree(
+        ref HevcCabacSyntaxReader reader,
+        int x,
+        int y,
+        int log2Size,
+        int depth,
+        int regionId,
+        int colorPlaneIndex)
+    {
+        int size = 1 << log2Size;
+        bool crossesPictureBoundary = x + size > this.sequenceParameterSet.Width || y + size > this.sequenceParameterSet.Height;
+        bool canSplit = log2Size > this.sequenceParameterSet.MinCodingBlockLog2;
+        HevcCodingTreeState codingTreeState = this.codingTreeStates[colorPlaneIndex];
+        bool split = false;
+        if (canSplit)
+        {
+            if (crossesPictureBoundary)
+            {
+                split = true;
+            }
+            else
+            {
+                bool leftAvailable = this.reconstructionState.IsReconstructed((HevcPlane)colorPlaneIndex, x - 1, y, regionId);
+                bool aboveAvailable = this.reconstructionState.IsReconstructed((HevcPlane)colorPlaneIndex, x, y - 1, regionId);
+                int context = codingTreeState.GetSplitContext(x, y, depth, leftAvailable, aboveAvailable);
+                split = reader.ReadSplit(context);
+            }
+        }
+
+        if (depth == this.pictureParameterSet.QuantizationParameterDeltaDepth
+            && this.pictureParameterSet.CodingUnitQuantizationParameterDeltaEnabled)
+        {
+            this.BeginQuantizationGroup(x, y, regionId, colorPlaneIndex);
+        }
+
+        if (depth == this.pictureParameterSet.ChromaQuantizationParameterOffsetDepth
+            && this.pictureParameterSet.ChromaQuantizationParameterOffsetsCb.Count != 0)
+        {
+            this.currentChromaQuantizationAdjustment = 0;
+            this.chromaQuantizationAdjustmentPending = true;
+        }
+
+        if (split)
+        {
+            int childLog2Size = log2Size - 1;
+            int childSize = 1 << childLog2Size;
+            for (int child = 0; child < 4; child++)
+            {
+                int childX = x + ((child & 1) * childSize);
+                int childY = y + ((child >> 1) * childSize);
+                if (childX >= this.sequenceParameterSet.Width || childY >= this.sequenceParameterSet.Height)
+                {
+                    continue;
+                }
+
+                if (this.DecodeCodingTree(
+                    ref reader,
+                    childX,
+                    childY,
+                    childLog2Size,
+                    depth + 1,
+                    regionId,
+                    colorPlaneIndex))
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        return this.DecodeCodingUnit(ref reader, x, y, log2Size, depth, regionId, colorPlaneIndex);
+    }
+
+    /// <summary>
+    /// Decodes and reconstructs one intra-coded leaf coding unit.
+    /// </summary>
+    /// <param name="reader">The active entropy-substream reader.</param>
+    /// <param name="x">The coding-unit left luma coordinate.</param>
+    /// <param name="y">The coding-unit top luma coordinate.</param>
+    /// <param name="log2Size">The base-two logarithm of the coding-unit side.</param>
+    /// <param name="depth">The coding-tree depth.</param>
+    /// <param name="regionId">The current independent-slice and tile prediction region.</param>
+    /// <param name="colorPlaneIndex">The selected separate-color plane, or zero for combined coding.</param>
+    /// <returns><see langword="true"/> when this coding unit terminates the slice segment.</returns>
+    private bool DecodeCodingUnit(
+        ref HevcCabacSyntaxReader reader,
+        int x,
+        int y,
+        int log2Size,
+        int depth,
+        int regionId,
+        int colorPlaneIndex)
+    {
+        bool transquantBypass = this.pictureParameterSet.TransquantizationBypassEnabled && reader.ReadTransquantBypass();
+        bool usesNxNPartitions = reader.ReadIntraNxNPartition(log2Size == this.sequenceParameterSet.MinCodingBlockLog2);
+        HevcPlane primaryPlane = this.sequenceParameterSet.SeparateColorPlaneFlag ? (HevcPlane)colorPlaneIndex : HevcPlane.Y;
+        bool pcm = this.sequenceParameterSet.PcmEnabled
+            && !usesNxNPartitions
+            && log2Size >= this.sequenceParameterSet.MinPcmCodingBlockLog2
+            && log2Size <= this.sequenceParameterSet.MaxPcmCodingBlockLog2
+            && reader.ReadPcmFlag();
+
+        if (pcm)
+        {
+            int size = 1 << log2Size;
+            this.deblockingState.MarkBlock(primaryPlane, x, y, size, size);
+            this.DecodePcmCodingUnit(ref reader, x, y, log2Size, regionId, colorPlaneIndex);
+            reader.RestartAfterPcm();
+        }
+        else
+        {
+            HevcIntraPredictionState predictionState = this.intraPredictionStates[colorPlaneIndex];
+            HevcPlane boundaryPlane = this.sequenceParameterSet.SeparateColorPlaneFlag ? (HevcPlane)colorPlaneIndex : HevcPlane.Y;
+            bool leftAvailable = this.reconstructionState.IsReconstructed(boundaryPlane, x - 1, y, regionId);
+            bool aboveAvailable = this.reconstructionState.IsReconstructed(boundaryPlane, x, y - 1, regionId);
+            predictionState.DecodeLumaModes(ref reader, x, y, log2Size, usesNxNPartitions, leftAvailable, aboveAvailable);
+            if (this.sequenceParameterSet.ChromaFormat != 0 && !this.sequenceParameterSet.SeparateColorPlaneFlag)
+            {
+                predictionState.DecodeChromaMode(ref reader, x, y, log2Size);
+            }
+
+            int minimumTransformLog2 = GetMinimumTransformLog2Size(this.sequenceParameterSet, log2Size, usesNxNPartitions);
+            HevcTransformUnitGeometry geometry = HevcTransformUnitGeometry.CreateRoot(
+                x,
+                y,
+                log2Size,
+                this.sequenceParameterSet.ChromaFormat,
+                this.sequenceParameterSet.SeparateColorPlaneFlag,
+                colorPlaneIndex);
+
+            this.DecodeTransformTree(
+                ref reader,
+                in geometry,
+                0,
+                minimumTransformLog2,
+                usesNxNPartitions,
+                transquantBypass,
+                regionId,
+                colorPlaneIndex,
+                default,
+                default);
+        }
+
+        HevcQuantizationParameters quantizationParameters = this.CreateQuantizationParameters();
+        this.codingTreeStates[colorPlaneIndex].SetCodingUnit(
+            x,
+            y,
+            log2Size,
+            depth,
+            this.currentQuantizationParameter,
+            quantizationParameters.CbOffset,
+            quantizationParameters.CrOffset,
+            transquantBypass,
+            pcm);
+
+        this.lastCodedQuantizationParameter = this.currentQuantizationParameter;
+        return reader.ReadTerminate();
+    }
+
+    /// <summary>
+    /// Begins one luma quantization group using available spatial predictors.
+    /// </summary>
+    /// <param name="x">The quantization-group left luma coordinate.</param>
+    /// <param name="y">The quantization-group top luma coordinate.</param>
+    /// <param name="regionId">The current independent-slice and tile prediction region.</param>
+    /// <param name="colorPlaneIndex">The selected separate-color plane, or zero for combined coding.</param>
+    private void BeginQuantizationGroup(int x, int y, int regionId, int colorPlaneIndex)
+    {
+        HevcPlane plane = this.sequenceParameterSet.SeparateColorPlaneFlag ? (HevcPlane)colorPlaneIndex : HevcPlane.Y;
+        bool leftAvailable = this.reconstructionState.IsReconstructed(plane, x - 1, y, regionId);
+        bool aboveAvailable = this.reconstructionState.IsReconstructed(plane, x, y - 1, regionId);
+        int fallback = this.lastCodedQuantizationParameter;
+        HevcCodingTreeState codingTreeState = this.codingTreeStates[colorPlaneIndex];
+        int left = leftAvailable ? codingTreeState.GetQuantizationParameter(x - 1, y) : fallback;
+        int above = aboveAvailable ? codingTreeState.GetQuantizationParameter(x, y - 1) : fallback;
+        this.currentQuantizationParameter = (left + above + 1) >> 1;
+        this.quantizationParameterDeltaPending = true;
+    }
+
+    /// <summary>
+    /// Derives the smallest luma transform permitted within one intra coding unit.
+    /// </summary>
+    /// <param name="sequenceParameterSet">The transform hierarchy limits.</param>
+    /// <param name="codingUnitLog2Size">The base-two logarithm of the coding-unit side.</param>
+    /// <param name="usesNxNPartitions">Whether the coding unit has four luma prediction partitions.</param>
+    /// <returns>The minimum luma transform side as a base-two logarithm.</returns>
+    private static int GetMinimumTransformLog2Size(
+        HevcSequenceParameterSet sequenceParameterSet,
+        int codingUnitLog2Size,
+        bool usesNxNPartitions)
+    {
+        int hierarchyReduction = sequenceParameterSet.MaxTransformHierarchyDepthIntra - 1 + (usesNxNPartitions ? 1 : 0);
+        int minimum = codingUnitLog2Size < sequenceParameterSet.MinTransformBlockLog2 + hierarchyReduction
+            ? sequenceParameterSet.MinTransformBlockLog2
+            : codingUnitLog2Size - hierarchyReduction;
+
+        return Math.Min(minimum, sequenceParameterSet.MaxTransformBlockLog2);
+    }
+}

src/ImageSharp/Formats/Heif/Hevc/HevcPictureDecoder.cs

@@ -0,0 +1,299 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers;
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <summary>
+/// Owns the bounded state used to reconstruct one independently decodable HEVC still picture.
+/// </summary>
+internal sealed partial class HevcPictureDecoder : IDisposable
+{
+    /// <summary>
+    /// The maximum square transform-block sample count.
+    /// </summary>
+    private const int MaximumTransformSampleCount = 32 * 32;
+
+    /// <summary>
+    /// The largest reference array used by a thirty-two-sample prediction block.
+    /// </summary>
+    private const int MaximumReferenceLength = (2 * 32) + 1;
+
+    /// <summary>
+    /// The configuration providing picture-lifetime allocations.
+    /// </summary>
+    private readonly Configuration configuration;
+
+    /// <summary>
+    /// The active picture parameters.
+    /// </summary>
+    private readonly HevcPictureParameterSet pictureParameterSet;
+
+    /// <summary>
+    /// The active sequence parameters.
+    /// </summary>
+    private readonly HevcSequenceParameterSet sequenceParameterSet;
+
+    /// <summary>
+    /// The decoded coding-unit state.
+    /// </summary>
+    private readonly HevcCodingTreeState[] codingTreeStates;
+
+    /// <summary>
+    /// The decoded intra-prediction modes.
+    /// </summary>
+    private readonly HevcIntraPredictionState[] intraPredictionStates;
+
+    /// <summary>
+    /// The completed prediction-block state used for reference availability.
+    /// </summary>
+    private readonly HevcReconstructionState reconstructionState;
+
+    /// <summary>
+    /// The reusable coefficient entropy decoder.
+    /// </summary>
+    private readonly HevcCoefficientDecoder coefficientDecoder;
+
+    /// <summary>
+    /// The resolved sample-adaptive-offset parameters for every coding-tree block.
+    /// </summary>
+    private readonly HevcSampleAdaptiveOffsetState sampleAdaptiveOffsetState;
+
+    /// <summary>
+    /// The transform and prediction boundaries required by the deblocking stage.
+    /// </summary>
+    private readonly HevcDeblockingState deblockingState;
+
+    /// <summary>
+    /// The integer coefficient, residual, and transform workspace.
+    /// </summary>
+    private readonly IMemoryOwner<int> integerScratch;
+
+    /// <summary>
+    /// The prediction, reference, and reference-substitution workspace.
+    /// </summary>
+    private readonly IMemoryOwner<ushort> predictionScratch;
+
+    /// <summary>
+    /// The ordered intra-reference availability workspace.
+    /// </summary>
+    private readonly IMemoryOwner<bool> availabilityScratch;
+
+    /// <summary>
+    /// The adaptive contexts captured after the second coding-tree block of a wavefront row.
+    /// </summary>
+    private readonly HevcCabacContext[] wavefrontContexts = new HevcCabacContext[HevcCabacContexts.ContextCount];
+
+    /// <summary>
+    /// The persistent Rice statistics captured with the wavefront probability contexts.
+    /// </summary>
+    private InlineArray4<int> wavefrontRiceAdaptation;
+
+    /// <summary>
+    /// The adaptive contexts retained at the end of a dependent-slice prediction region.
+    /// </summary>
+    private readonly HevcCabacContext[] sliceSegmentContexts = new HevcCabacContext[HevcCabacContexts.ContextCount * 3];
+
+    /// <summary>
+    /// The persistent Rice statistics retained with dependent-slice probability contexts.
+    /// </summary>
+    private readonly int[] sliceSegmentRiceAdaptation = new int[12];
+
+    /// <summary>
+    /// Whether retained dependent-slice contexts are available.
+    /// </summary>
+    private InlineArray4<bool> hasSliceSegmentContexts;
+
+    /// <summary>
+    /// The luma quantization parameter most recently coded in the current prediction region.
+    /// </summary>
+    private int lastCodedQuantizationParameter;
+
+    /// <summary>
+    /// The effective luma quantization parameter of the current quantization group.
+    /// </summary>
+    private int currentQuantizationParameter;
+
+    /// <summary>
+    /// The one-based chroma quantization-offset-list selector of the current quantization group.
+    /// </summary>
+    private int currentChromaQuantizationAdjustment;
+
+    /// <summary>
+    /// The Cb quantization-parameter offset signaled by the governing independent slice.
+    /// </summary>
+    private int currentSliceChromaBlueQuantizationOffset;
+
+    /// <summary>
+    /// The Cr quantization-parameter offset signaled by the governing independent slice.
+    /// </summary>
+    private int currentSliceChromaRedQuantizationOffset;
+
+    /// <summary>
+    /// Whether the current quantization group can still signal its luma delta.
+    /// </summary>
+    private bool quantizationParameterDeltaPending;
+
+    /// <summary>
+    /// Whether the current quantization group can still signal its chroma adjustment.
+    /// </summary>
+    private bool chromaQuantizationAdjustmentPending;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcPictureDecoder"/> class.
+    /// </summary>
+    /// <param name="configuration">The configuration providing all decoder-owned memory.</param>
+    /// <param name="pictureParameterSet">The picture parameters governing the coded still image.</param>
+    public HevcPictureDecoder(Configuration configuration, HevcPictureParameterSet pictureParameterSet)
+    {
+        this.configuration = configuration;
+        this.pictureParameterSet = pictureParameterSet;
+        this.sequenceParameterSet = pictureParameterSet.SequenceParameterSet;
+        this.Picture = new HevcPictureBuffer(configuration, this.sequenceParameterSet);
+        int codingTreeStateCount = this.sequenceParameterSet.SeparateColorPlaneFlag ? 3 : 1;
+        this.codingTreeStates = new HevcCodingTreeState[codingTreeStateCount];
+        for (int index = 0; index < this.codingTreeStates.Length; index++)
+        {
+            this.codingTreeStates[index] = new HevcCodingTreeState(configuration, this.sequenceParameterSet);
+        }
+
+        int intraPredictionStateCount = this.sequenceParameterSet.SeparateColorPlaneFlag ? 3 : 1;
+        this.intraPredictionStates = new HevcIntraPredictionState[intraPredictionStateCount];
+        for (int index = 0; index < this.intraPredictionStates.Length; index++)
+        {
+            this.intraPredictionStates[index] = new HevcIntraPredictionState(configuration, this.sequenceParameterSet);
+        }
+
+        this.reconstructionState = new HevcReconstructionState(configuration, this.sequenceParameterSet);
+        this.coefficientDecoder = new HevcCoefficientDecoder(configuration);
+        int codingTreeBlockCount = HevcParameterSetSyntax.GetCodingTreeBlockCount(
+            this.sequenceParameterSet.Width,
+            this.sequenceParameterSet.CodingTreeBlockLog2)
+            * HevcParameterSetSyntax.GetCodingTreeBlockCount(
+                this.sequenceParameterSet.Height,
+                this.sequenceParameterSet.CodingTreeBlockLog2);
+
+        this.sampleAdaptiveOffsetState = new HevcSampleAdaptiveOffsetState(configuration, codingTreeBlockCount);
+        this.deblockingState = new HevcDeblockingState(configuration, this.sequenceParameterSet);
+
+        // Six transform-sized integer regions retain quantized, dequantized, reconstructed, cross-component, and
+        // two-pass inverse-transform data without allocating in coding-unit or transform-unit loops.
+        this.integerScratch = configuration.MemoryAllocator.Allocate<int>(MaximumTransformSampleCount * 6);
+        int maximumPredictionScratch = HevcIntraPredictor.GetScratchLength(5);
+        int maximumReferenceScratch = HevcIntraPredictor.GetReferenceScratchLength(5, 4);
+        this.predictionScratch = configuration.MemoryAllocator.Allocate<ushort>(
+            MaximumTransformSampleCount + maximumPredictionScratch + maximumReferenceScratch + (MaximumReferenceLength * 4));
+
+        this.availabilityScratch = configuration.MemoryAllocator.Allocate<bool>((4 * 32 / 2) + 1);
+    }
+
+    /// <summary>
+    /// Gets the native-precision reconstructed component planes.
+    /// </summary>
+    public HevcPictureBuffer Picture { get; }
+
+    /// <summary>
+    /// Reconstructs every ordered slice segment in one independently decodable image item.
+    /// </summary>
+    /// <param name="bitstream">The validated image-item NAL units and slice segments.</param>
+    /// <exception cref="InvalidImageContentException">
+    /// A slice changes the coded picture parameters, overlaps an earlier segment, or does not terminate at a valid
+    /// coding-tree boundary.
+    /// </exception>
+    public void Decode(HevcImageItemBitstream bitstream)
+    {
+        HevcTileLayout tileLayout = new(this.pictureParameterSet);
+        int planeCount = this.sequenceParameterSet.SeparateColorPlaneFlag ? 3 : 1;
+        int[] nextCodingTreeBlockAddressesInTileScan = new int[planeCount];
+        int[] independentSliceIndices = new int[planeCount];
+        HevcSliceSegmentHeader?[] independentSlices = new HevcSliceSegmentHeader?[planeCount];
+        for (int sliceIndex = 0; sliceIndex < bitstream.SliceSegments.Count; sliceIndex++)
+        {
+            HevcSliceSegmentHeader slice = bitstream.SliceSegments[sliceIndex];
+            int colorPlane = this.sequenceParameterSet.SeparateColorPlaneFlag ? slice.ColorPlaneId : 0;
+            if (slice.PictureParameterSet.Id != this.pictureParameterSet.Id
+                || slice.PictureParameterSet.SequenceParameterSetId != this.pictureParameterSet.SequenceParameterSetId)
+            {
+                throw new InvalidImageContentException("The HEVC still picture changes parameter sets between slice segments.");
+            }
+
+            if (!slice.DependentSliceSegment)
+            {
+                independentSlices[colorPlane] = slice;
+                independentSliceIndices[colorPlane]++;
+            }
+
+            HevcSliceSegmentHeader? independentSlice = independentSlices[colorPlane];
+            if (independentSlice is null)
+            {
+                throw new InvalidImageContentException("The HEVC still picture begins with a dependent slice segment.");
+            }
+
+            int sliceStartAddressInTileScan = tileLayout.GetTileScanAddress(slice.SliceSegmentAddress);
+            if (sliceStartAddressInTileScan != nextCodingTreeBlockAddressesInTileScan[colorPlane])
+            {
+                throw new InvalidImageContentException("The HEVC slice segments do not cover the coded picture in order.");
+            }
+
+            nextCodingTreeBlockAddressesInTileScan[colorPlane] = this.DecodeSliceSegment(
+                slice,
+                independentSlice,
+                independentSliceIndices[colorPlane],
+                in tileLayout,
+                sliceStartAddressInTileScan,
+                tileLayout.GetTileScanAddress(independentSlice.SliceSegmentAddress));
+        }
+
+        int codingTreeBlockCount = HevcParameterSetSyntax.GetCodingTreeBlockCount(
+            this.sequenceParameterSet.Width,
+            this.sequenceParameterSet.CodingTreeBlockLog2)
+            * HevcParameterSetSyntax.GetCodingTreeBlockCount(
+                this.sequenceParameterSet.Height,
+                this.sequenceParameterSet.CodingTreeBlockLog2);
+
+        foreach (int nextAddress in nextCodingTreeBlockAddressesInTileScan)
+        {
+            if (nextAddress != codingTreeBlockCount)
+            {
+                throw new InvalidImageContentException("The HEVC slice segments do not reconstruct the complete coded picture.");
+            }
+        }
+
+        this.ApplyDeblockingFilter(in tileLayout);
+        if (this.sampleAdaptiveOffsetState.HasEnabledParameters)
+        {
+            // SAO classification always observes the complete post-deblocking picture, never samples already offset by an
+            // earlier CTB. One picture-lifetime snapshot provides that invariant without row allocations or filter-order coupling.
+            using HevcPictureBuffer sampleAdaptiveOffsetSource = new(this.configuration, this.sequenceParameterSet);
+            this.Picture.CopyTo(sampleAdaptiveOffsetSource);
+            this.ApplySampleAdaptiveOffset(sampleAdaptiveOffsetSource, in tileLayout);
+        }
+    }
+
+    /// <summary>
+    /// Releases all current-picture state and reconstructed planes.
+    /// </summary>
+    public void Dispose()
+    {
+        this.availabilityScratch.Dispose();
+        this.predictionScratch.Dispose();
+        this.integerScratch.Dispose();
+        this.deblockingState.Dispose();
+        this.sampleAdaptiveOffsetState.Dispose();
+        this.coefficientDecoder.Dispose();
+        this.reconstructionState.Dispose();
+        foreach (HevcIntraPredictionState state in this.intraPredictionStates)
+        {
+            state.Dispose();
+        }
+
+        foreach (HevcCodingTreeState state in this.codingTreeStates)
+        {
+            state.Dispose();
+        }
+
+        this.Picture.Dispose();
+    }
+}

src/ImageSharp/Formats/Heif/Hevc/HevcQuantizationParameters.cs

@@ -27,6 +27,8 @@ internal readonly struct HevcQuantizationParameters
     {
         int lumaBitDepthOffset = 6 * (lumaBitDepth - 8);
         int chromaBitDepthOffset = 6 * (chromaBitDepth - 8);
+        this.CbOffset = cbQuantizationParameterOffset;
+        this.CrOffset = crQuantizationParameterOffset;
         this.Luma = lumaQuantizationParameter + lumaBitDepthOffset;
         this.Cb = GetChromaQuantizationParameter(lumaQuantizationParameter, cbQuantizationParameterOffset, chromaBitDepthOffset, chromaFormat);
         this.Cr = GetChromaQuantizationParameter(lumaQuantizationParameter, crQuantizationParameterOffset, chromaBitDepthOffset, chromaFormat);
@@ -47,6 +49,16 @@ internal readonly struct HevcQuantizationParameters
     /// </summary>
     public int Cr { get; }
 
+    /// <summary>
+    /// Gets the combined picture, slice, and coding-unit Cb quantization-parameter offset.
+    /// </summary>
+    public int CbOffset { get; }
+
+    /// <summary>
+    /// Gets the combined picture, slice, and coding-unit Cr quantization-parameter offset.
+    /// </summary>
+    public int CrOffset { get; }
+
     /// <summary>
     /// Gets the H.265 Table 8-10 chroma quantization-parameter mapping for 4:2:0 pictures.
     /// </summary>
@@ -76,7 +88,7 @@ internal readonly struct HevcQuantizationParameters
     /// <param name="chromaBitDepthOffset">Six times the number of chroma bits above eight.</param>
     /// <param name="chromaFormat">The sequence chroma-format identifier.</param>
     /// <returns>The effective nonnegative chroma quantization parameter including its bit-depth offset.</returns>
-    private static int GetChromaQuantizationParameter(
+    public static int GetChromaQuantizationParameter(
         int lumaQuantizationParameter,
         int componentOffset,
         int chromaBitDepthOffset,

src/ImageSharp/Formats/Heif/Hevc/HevcReconstructionState.cs

@@ -0,0 +1,221 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <summary>
+/// Tracks reconstructed minimum prediction blocks for HEVC intra-reference availability.
+/// </summary>
+internal sealed class HevcReconstructionState : IDisposable
+{
+    /// <summary>
+    /// The base-two logarithm of the minimum luma prediction-block side.
+    /// </summary>
+    private const int MinPredictionBlockLog2 = 2;
+
+    /// <summary>
+    /// The reconstruction-region identifiers for the three component planes.
+    /// </summary>
+    private readonly Buffer2D<int>[] regions;
+
+    /// <summary>
+    /// The horizontal chroma subsampling shift.
+    /// </summary>
+    private readonly int chromaSubsamplingX;
+
+    /// <summary>
+    /// The vertical chroma subsampling shift.
+    /// </summary>
+    private readonly int chromaSubsamplingY;
+
+    /// <summary>
+    /// The coded luma width used to reject padded right-edge units.
+    /// </summary>
+    private readonly int width;
+
+    /// <summary>
+    /// The coded luma height used to reject padded bottom-edge units.
+    /// </summary>
+    private readonly int height;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcReconstructionState"/> class.
+    /// </summary>
+    /// <param name="configuration">The configuration providing the image memory allocator.</param>
+    /// <param name="sequenceParameterSet">The coded picture and chroma geometry.</param>
+    public HevcReconstructionState(Configuration configuration, HevcSequenceParameterSet sequenceParameterSet)
+    {
+        this.width = sequenceParameterSet.Width;
+        this.height = sequenceParameterSet.Height;
+        int widthInUnits = DivideCeilingByPowerOfTwo(this.width, MinPredictionBlockLog2);
+        int heightInUnits = DivideCeilingByPowerOfTwo(this.height, MinPredictionBlockLog2);
+        this.chromaSubsamplingX = !sequenceParameterSet.SeparateColorPlaneFlag && sequenceParameterSet.ChromaFormat is 1 or 2 ? 1 : 0;
+        this.chromaSubsamplingY = !sequenceParameterSet.SeparateColorPlaneFlag && sequenceParameterSet.ChromaFormat == 1 ? 1 : 0;
+        this.regions =
+        [
+            configuration.MemoryAllocator.Allocate2D<int>(widthInUnits, heightInUnits),
+            configuration.MemoryAllocator.Allocate2D<int>(widthInUnits, heightInUnits),
+            configuration.MemoryAllocator.Allocate2D<int>(widthInUnits, heightInUnits),
+        ];
+    }
+
+    /// <summary>
+    /// Gets the horizontal availability-unit width for a component plane.
+    /// </summary>
+    /// <param name="plane">The component plane.</param>
+    /// <returns>The availability-unit width in component samples.</returns>
+    public int GetUnitWidth(HevcPlane plane) => 1 << (MinPredictionBlockLog2 - this.GetSubsamplingX(plane));
+
+    /// <summary>
+    /// Gets the vertical availability-unit height for a component plane.
+    /// </summary>
+    /// <param name="plane">The component plane.</param>
+    /// <returns>The availability-unit height in component samples.</returns>
+    public int GetUnitHeight(HevcPlane plane) => 1 << (MinPredictionBlockLog2 - this.GetSubsamplingY(plane));
+
+    /// <summary>
+    /// Marks a reconstructed component rectangle as available within one slice-and-tile prediction region.
+    /// </summary>
+    /// <param name="plane">The reconstructed component plane.</param>
+    /// <param name="x">The rectangle left coordinate in component samples.</param>
+    /// <param name="y">The rectangle top coordinate in component samples.</param>
+    /// <param name="width">The rectangle width in component samples.</param>
+    /// <param name="height">The rectangle height in component samples.</param>
+    /// <param name="regionId">The positive identifier shared by prediction blocks in the same slice segment and tile.</param>
+    public void MarkReconstructed(HevcPlane plane, int x, int y, int width, int height, int regionId)
+    {
+        DebugGuard.MustBeGreaterThan(regionId, 0, nameof(regionId));
+        int subsamplingX = this.GetSubsamplingX(plane);
+        int subsamplingY = this.GetSubsamplingY(plane);
+        int unitX = (x << subsamplingX) >> MinPredictionBlockLog2;
+        int unitY = (y << subsamplingY) >> MinPredictionBlockLog2;
+        int endX = DivideCeilingByPowerOfTwo((x + width) << subsamplingX, MinPredictionBlockLog2);
+        int endY = DivideCeilingByPowerOfTwo((y + height) << subsamplingY, MinPredictionBlockLog2);
+        Buffer2D<int> map = this.regions[(int)plane];
+        endX = Math.Min(endX, map.Width);
+        endY = Math.Min(endY, map.Height);
+
+        // Chroma availability units map back to the same four-by-four luma grid used by HEVC neighbor derivation.
+        // Filling the complete rectangle makes later sub-TUs observe only samples whose reconstruction has finished.
+        for (int row = unitY; row < endY; row++)
+        {
+            map.DangerousGetRowSpan(row)[unitX..endX].Fill(regionId);
+        }
+    }
+
+    /// <summary>
+    /// Builds the ordered availability flags consumed by HEVC reference-sample substitution.
+    /// </summary>
+    /// <param name="plane">The component plane containing the prediction block.</param>
+    /// <param name="x">The prediction-block left coordinate in component samples.</param>
+    /// <param name="y">The prediction-block top coordinate in component samples.</param>
+    /// <param name="log2Size">The base-two logarithm of the square prediction-block side.</param>
+    /// <param name="regionId">The current slice-and-tile prediction-region identifier.</param>
+    /// <param name="destination">
+    /// The destination ordered from the bottom-most below-left unit through top-left and then the above-right units.
+    /// </param>
+    /// <returns>The number of flags written.</returns>
+    public int BuildReferenceAvailability(HevcPlane plane, int x, int y, int log2Size, int regionId, Span<bool> destination)
+    {
+        DebugGuard.MustBeBetweenOrEqualTo(log2Size, 2, 5, nameof(log2Size));
+        DebugGuard.MustBeGreaterThan(regionId, 0, nameof(regionId));
+        int size = 1 << log2Size;
+        int unitWidth = this.GetUnitWidth(plane);
+        int unitHeight = this.GetUnitHeight(plane);
+        int leftUnitCount = (size * 2) / unitHeight;
+        int aboveUnitCount = (size * 2) / unitWidth;
+        int flagCount = leftUnitCount + aboveUnitCount + 1;
+        Span<bool> availability = destination[..flagCount];
+
+        for (int unit = 0; unit < leftUnitCount; unit++)
+        {
+            int unitY = y + ((leftUnitCount - unit - 1) * unitHeight);
+            availability[unit] = this.IsAvailable(plane, x - 1, unitY, regionId);
+        }
+
+        availability[leftUnitCount] = this.IsAvailable(plane, x - 1, y - 1, regionId);
+        for (int unit = 0; unit < aboveUnitCount; unit++)
+        {
+            availability[leftUnitCount + unit + 1] = this.IsAvailable(plane, x + (unit * unitWidth), y - 1, regionId);
+        }
+
+        return flagCount;
+    }
+
+    /// <summary>
+    /// Gets whether one component sample has already been reconstructed in the selected prediction region.
+    /// </summary>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The component sample X coordinate.</param>
+    /// <param name="y">The component sample Y coordinate.</param>
+    /// <param name="regionId">The current slice-and-tile prediction-region identifier.</param>
+    /// <returns><see langword="true"/> when the sample is available; otherwise, <see langword="false"/>.</returns>
+    public bool IsReconstructed(HevcPlane plane, int x, int y, int regionId) => this.IsAvailable(plane, x, y, regionId);
+
+    /// <summary>
+    /// Releases the owned reconstruction-region maps.
+    /// </summary>
+    public void Dispose()
+    {
+        foreach (Buffer2D<int> map in this.regions)
+        {
+            map.Dispose();
+        }
+    }
+
+    /// <summary>
+    /// Gets whether a component sample belongs to an already reconstructed block in the selected prediction region.
+    /// </summary>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The component sample X coordinate.</param>
+    /// <param name="y">The component sample Y coordinate.</param>
+    /// <param name="regionId">The current slice-and-tile prediction-region identifier.</param>
+    /// <returns><see langword="true"/> when the sample is available; otherwise, <see langword="false"/>.</returns>
+    private bool IsAvailable(HevcPlane plane, int x, int y, int regionId)
+    {
+        if (x < 0 || y < 0)
+        {
+            return false;
+        }
+
+        int subsamplingX = this.GetSubsamplingX(plane);
+        int subsamplingY = this.GetSubsamplingY(plane);
+        int planeWidth = DivideCeilingByPowerOfTwo(this.width, subsamplingX);
+        int planeHeight = DivideCeilingByPowerOfTwo(this.height, subsamplingY);
+        if (x >= planeWidth || y >= planeHeight)
+        {
+            return false;
+        }
+
+        int unitX = (x << subsamplingX) >> MinPredictionBlockLog2;
+        int unitY = (y << subsamplingY) >> MinPredictionBlockLog2;
+        Buffer2D<int> map = this.regions[(int)plane];
+        return (uint)unitX < (uint)map.Width
+            && (uint)unitY < (uint)map.Height
+            && map.DangerousGetRowSpan(unitY)[unitX] == regionId;
+    }
+
+    /// <summary>
+    /// Gets the horizontal chroma shift selected by a component plane.
+    /// </summary>
+    /// <param name="plane">The component plane.</param>
+    /// <returns>Zero for luma and full-resolution planes; otherwise, the chroma shift.</returns>
+    private int GetSubsamplingX(HevcPlane plane) => plane == HevcPlane.Y ? 0 : this.chromaSubsamplingX;
+
+    /// <summary>
+    /// Gets the vertical chroma shift selected by a component plane.
+    /// </summary>
+    /// <param name="plane">The component plane.</param>
+    /// <returns>Zero for luma and full-resolution planes; otherwise, the chroma shift.</returns>
+    private int GetSubsamplingY(HevcPlane plane) => plane == HevcPlane.Y ? 0 : this.chromaSubsamplingY;
+
+    /// <summary>
+    /// Divides a nonnegative sample count by a power of two with upward rounding.
+    /// </summary>
+    /// <param name="value">The sample count.</param>
+    /// <param name="shift">The base-two divisor logarithm.</param>
+    /// <returns>The upward-rounded quotient.</returns>
+    private static int DivideCeilingByPowerOfTwo(int value, int shift) => (value + (1 << shift) - 1) >> shift;
+}

src/ImageSharp/Formats/Heif/Hevc/HevcResidualReconstructor.cs

@@ -164,6 +164,113 @@ internal static class HevcResidualReconstructor
         }
     }
 
+    /// <summary>
+    /// Adds the scaled luma residual to one chroma residual block for inverse cross-component prediction.
+    /// </summary>
+    /// <param name="lumaResidual">The packed luma residual samples colocated with the chroma block.</param>
+    /// <param name="chromaResidual">The packed chroma residual block updated in place.</param>
+    /// <param name="sampleCount">The number of residual samples in each block.</param>
+    /// <param name="alpha">The signed cross-component scale from minus eight through eight.</param>
+    /// <param name="bitDepthDifference">The luma bit depth minus the chroma bit depth.</param>
+    public static void ApplyCrossComponentPrediction(
+        ReadOnlySpan<int> lumaResidual,
+        Span<int> chromaResidual,
+        int sampleCount,
+        int alpha,
+        int bitDepthDifference)
+    {
+        ref int lumaBase = ref MemoryMarshal.GetReference(lumaResidual);
+        ref int chromaBase = ref MemoryMarshal.GetReference(chromaResidual);
+        int index = 0;
+
+        // The scale denominator is eight. Adjusting luma precision first preserves the normative arithmetic shift
+        // for negative residuals before the signed alpha multiplication is applied independently to every lane.
+        if (Vector512.IsHardwareAccelerated)
+        {
+            Vector512<int> alphaVector = Vector512.Create(alpha);
+            Vector512<int> minimum = Vector512.Create(ResidualMinimum);
+            Vector512<int> maximum = Vector512.Create(ResidualMaximum);
+            for (; index <= sampleCount - Vector512<int>.Count; index += Vector512<int>.Count)
+            {
+                Vector512<int> luma = AdjustBitDepth(Vector512.LoadUnsafe(ref lumaBase, (nuint)index), bitDepthDifference);
+                Vector512<int> chroma = Vector512.LoadUnsafe(ref chromaBase, (nuint)index);
+                Vector512.Clamp(chroma + ((luma * alphaVector) >> 3), minimum, maximum).StoreUnsafe(ref chromaBase, (nuint)index);
+            }
+        }
+
+        if (Vector256.IsHardwareAccelerated)
+        {
+            Vector256<int> alphaVector = Vector256.Create(alpha);
+            Vector256<int> minimum = Vector256.Create(ResidualMinimum);
+            Vector256<int> maximum = Vector256.Create(ResidualMaximum);
+            for (; index <= sampleCount - Vector256<int>.Count; index += Vector256<int>.Count)
+            {
+                Vector256<int> luma = AdjustBitDepth(Vector256.LoadUnsafe(ref lumaBase, (nuint)index), bitDepthDifference);
+                Vector256<int> chroma = Vector256.LoadUnsafe(ref chromaBase, (nuint)index);
+                Vector256.Clamp(chroma + ((luma * alphaVector) >> 3), minimum, maximum).StoreUnsafe(ref chromaBase, (nuint)index);
+            }
+        }
+
+        if (Vector128.IsHardwareAccelerated)
+        {
+            Vector128<int> alphaVector = Vector128.Create(alpha);
+            Vector128<int> minimum = Vector128.Create(ResidualMinimum);
+            Vector128<int> maximum = Vector128.Create(ResidualMaximum);
+            for (; index <= sampleCount - Vector128<int>.Count; index += Vector128<int>.Count)
+            {
+                Vector128<int> luma = AdjustBitDepth(Vector128.LoadUnsafe(ref lumaBase, (nuint)index), bitDepthDifference);
+                Vector128<int> chroma = Vector128.LoadUnsafe(ref chromaBase, (nuint)index);
+                Vector128.Clamp(chroma + ((luma * alphaVector) >> 3), minimum, maximum).StoreUnsafe(ref chromaBase, (nuint)index);
+            }
+        }
+
+        for (; index < sampleCount; index++)
+        {
+            int luma = AdjustBitDepth(Unsafe.Add(ref lumaBase, index), bitDepthDifference);
+            int chroma = Unsafe.Add(ref chromaBase, index) + ((alpha * luma) >> 3);
+            Unsafe.Add(ref chromaBase, index) = Math.Clamp(chroma, ResidualMinimum, ResidualMaximum);
+        }
+    }
+
+    /// <summary>
+    /// Adjusts sixteen luma residuals to chroma precision.
+    /// </summary>
+    /// <param name="values">The luma residuals.</param>
+    /// <param name="difference">The luma bit depth minus the chroma bit depth.</param>
+    /// <returns>The precision-adjusted residuals.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static Vector512<int> AdjustBitDepth(Vector512<int> values, int difference)
+        => difference >= 0 ? values >> difference : values << -difference;
+
+    /// <summary>
+    /// Adjusts eight luma residuals to chroma precision.
+    /// </summary>
+    /// <param name="values">The luma residuals.</param>
+    /// <param name="difference">The luma bit depth minus the chroma bit depth.</param>
+    /// <returns>The precision-adjusted residuals.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static Vector256<int> AdjustBitDepth(Vector256<int> values, int difference)
+        => difference >= 0 ? values >> difference : values << -difference;
+
+    /// <summary>
+    /// Adjusts four luma residuals to chroma precision.
+    /// </summary>
+    /// <param name="values">The luma residuals.</param>
+    /// <param name="difference">The luma bit depth minus the chroma bit depth.</param>
+    /// <returns>The precision-adjusted residuals.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static Vector128<int> AdjustBitDepth(Vector128<int> values, int difference)
+        => difference >= 0 ? values >> difference : values << -difference;
+
+    /// <summary>
+    /// Adjusts one luma residual to chroma precision.
+    /// </summary>
+    /// <param name="value">The luma residual.</param>
+    /// <param name="difference">The luma bit depth minus the chroma bit depth.</param>
+    /// <returns>The precision-adjusted residual.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static int AdjustBitDepth(int value, int difference) => difference >= 0 ? value >> difference : value << -difference;
+
     /// <summary>
     /// Applies one transform-skip normalization operator to a complete coefficient block.
     /// </summary>

src/ImageSharp/Formats/Heif/Hevc/HevcSampleAdaptiveOffsetFilter.cs

@@ -0,0 +1,733 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Runtime.Intrinsics;
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <summary>
+/// Applies HEVC sample-adaptive offsets to reconstructed component blocks.
+/// </summary>
+internal static class HevcSampleAdaptiveOffsetFilter
+{
+    /// <summary>
+    /// Defines the sample classifier shared by the SIMD row traversal and scalar tail.
+    /// </summary>
+    private interface ISampleClassifier
+    {
+        /// <summary>
+        /// Gets a value indicating whether classification reads the two neighboring sample rows.
+        /// </summary>
+        public static abstract bool UsesNeighbors { get; }
+
+        /// <summary>
+        /// Classifies thirty-two current samples against their two classifier inputs.
+        /// </summary>
+        /// <param name="current">The current sample lanes.</param>
+        /// <param name="neighbor0">The first neighboring sample lanes.</param>
+        /// <param name="neighbor1">The second neighboring sample lanes.</param>
+        /// <param name="kernel">The scaled offset and band-class state.</param>
+        /// <returns>The zero-based offset-table indices.</returns>
+        public static abstract Vector512<short> Classify(
+            Vector512<short> current,
+            Vector512<short> neighbor0,
+            Vector512<short> neighbor1,
+            in KernelParameters kernel);
+
+        /// <summary>
+        /// Classifies sixteen current samples against their two classifier inputs.
+        /// </summary>
+        /// <param name="current">The current sample lanes.</param>
+        /// <param name="neighbor0">The first neighboring sample lanes.</param>
+        /// <param name="neighbor1">The second neighboring sample lanes.</param>
+        /// <param name="kernel">The scaled offset and band-class state.</param>
+        /// <returns>The zero-based offset-table indices.</returns>
+        public static abstract Vector256<short> Classify(
+            Vector256<short> current,
+            Vector256<short> neighbor0,
+            Vector256<short> neighbor1,
+            in KernelParameters kernel);
+
+        /// <summary>
+        /// Classifies eight current samples against their two classifier inputs.
+        /// </summary>
+        /// <param name="current">The current sample lanes.</param>
+        /// <param name="neighbor0">The first neighboring sample lanes.</param>
+        /// <param name="neighbor1">The second neighboring sample lanes.</param>
+        /// <param name="kernel">The scaled offset and band-class state.</param>
+        /// <returns>The zero-based offset-table indices.</returns>
+        public static abstract Vector128<short> Classify(
+            Vector128<short> current,
+            Vector128<short> neighbor0,
+            Vector128<short> neighbor1,
+            in KernelParameters kernel);
+
+        /// <summary>
+        /// Classifies one current sample against its two classifier inputs.
+        /// </summary>
+        /// <param name="current">The current sample.</param>
+        /// <param name="neighbor0">The first neighboring sample.</param>
+        /// <param name="neighbor1">The second neighboring sample.</param>
+        /// <param name="kernel">The scaled offset and band-class state.</param>
+        /// <returns>The zero-based offset-table index.</returns>
+        public static abstract int Classify(short current, short neighbor0, short neighbor1, in KernelParameters kernel);
+    }
+
+    /// <summary>
+    /// Applies one resolved sample-adaptive-offset mode to a component coding-tree block.
+    /// </summary>
+    /// <param name="source">The immutable pre-SAO picture used for every classification.</param>
+    /// <param name="destination">The picture receiving filtered samples.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The block's left coordinate in component samples.</param>
+    /// <param name="y">The block's top coordinate in component samples.</param>
+    /// <param name="width">The block width in component samples.</param>
+    /// <param name="height">The block height in component samples.</param>
+    /// <param name="parameters">The resolved coded offsets and classifier.</param>
+    /// <param name="offsetScaleLog2">The component offset scale from the picture range-extension parameters.</param>
+    /// <param name="leftAvailable">Whether classification may read the block immediately to the left.</param>
+    /// <param name="rightAvailable">Whether classification may read the block immediately to the right.</param>
+    /// <param name="aboveAvailable">Whether classification may read the block immediately above.</param>
+    /// <param name="belowAvailable">Whether classification may read the block immediately below.</param>
+    /// <param name="aboveLeftAvailable">Whether classification may read the upper-left diagonal block.</param>
+    /// <param name="aboveRightAvailable">Whether classification may read the upper-right diagonal block.</param>
+    /// <param name="belowLeftAvailable">Whether classification may read the lower-left diagonal block.</param>
+    /// <param name="belowRightAvailable">Whether classification may read the lower-right diagonal block.</param>
+    public static void ApplyBlock(
+        HevcPictureBuffer source,
+        HevcPictureBuffer destination,
+        HevcPlane plane,
+        int x,
+        int y,
+        int width,
+        int height,
+        in HevcSampleAdaptiveOffsetParameters parameters,
+        int offsetScaleLog2,
+        bool leftAvailable,
+        bool rightAvailable,
+        bool aboveAvailable,
+        bool belowAvailable,
+        bool aboveLeftAvailable,
+        bool aboveRightAvailable,
+        bool belowLeftAvailable,
+        bool belowRightAvailable)
+    {
+        if (parameters.Type == HevcSampleAdaptiveOffsetType.Off)
+        {
+            return;
+        }
+
+        KernelParameters kernel = new(parameters, source.GetBitDepth(plane), offsetScaleLog2);
+        switch (parameters.Type)
+        {
+            case HevcSampleAdaptiveOffsetType.Band:
+                ApplyBand(source, destination, plane, x, y, width, height, in kernel);
+                break;
+            case HevcSampleAdaptiveOffsetType.EdgeHorizontal:
+                ApplyHorizontalEdges(source, destination, plane, x, y, width, height, leftAvailable, rightAvailable, in kernel);
+                break;
+            case HevcSampleAdaptiveOffsetType.EdgeVertical:
+                ApplyVerticalEdges(source, destination, plane, x, y, width, height, aboveAvailable, belowAvailable, in kernel);
+                break;
+            case HevcSampleAdaptiveOffsetType.EdgeDescending:
+                ApplyDescendingEdges(
+                    source,
+                    destination,
+                    plane,
+                    x,
+                    y,
+                    width,
+                    height,
+                    leftAvailable,
+                    rightAvailable,
+                    aboveAvailable,
+                    belowAvailable,
+                    aboveLeftAvailable,
+                    belowRightAvailable,
+                    in kernel);
+                break;
+            case HevcSampleAdaptiveOffsetType.EdgeAscending:
+                ApplyAscendingEdges(
+                    source,
+                    destination,
+                    plane,
+                    x,
+                    y,
+                    width,
+                    height,
+                    leftAvailable,
+                    rightAvailable,
+                    aboveAvailable,
+                    belowAvailable,
+                    aboveRightAvailable,
+                    belowLeftAvailable,
+                    in kernel);
+                break;
+        }
+    }
+
+    /// <summary>
+    /// Applies band offsets to every sample in a component block.
+    /// </summary>
+    /// <param name="source">The immutable pre-SAO picture.</param>
+    /// <param name="destination">The destination picture.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The block's left coordinate.</param>
+    /// <param name="y">The block's top coordinate.</param>
+    /// <param name="width">The block width.</param>
+    /// <param name="height">The block height.</param>
+    /// <param name="kernel">The scaled offset and band-class state.</param>
+    private static void ApplyBand(
+        HevcPictureBuffer source,
+        HevcPictureBuffer destination,
+        HevcPlane plane,
+        int x,
+        int y,
+        int width,
+        int height,
+        in KernelParameters kernel)
+    {
+        for (int row = y; row < y + height; row++)
+        {
+            ReadOnlySpan<ushort> sourceRow = source.GetRowSpan(plane, row).Slice(x, width);
+            Span<ushort> destinationRow = destination.GetRowSpan(plane, row).Slice(x, width);
+
+            // Band classification depends only on the current sample. The closed classifier's UsesNeighbors value removes
+            // the two neighbor loads when this generic traversal is specialized for BandClassifier.
+            ApplyRow<BandClassifier>(sourceRow, sourceRow, sourceRow, destinationRow, in kernel);
+        }
+    }
+
+    /// <summary>
+    /// Applies horizontal edge offsets within the available left and right boundaries.
+    /// </summary>
+    /// <param name="source">The immutable pre-SAO picture.</param>
+    /// <param name="destination">The destination picture.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The block's left coordinate.</param>
+    /// <param name="y">The block's top coordinate.</param>
+    /// <param name="width">The block width.</param>
+    /// <param name="height">The block height.</param>
+    /// <param name="leftAvailable">Whether the left neighboring block is available.</param>
+    /// <param name="rightAvailable">Whether the right neighboring block is available.</param>
+    /// <param name="kernel">The scaled offset state.</param>
+    private static void ApplyHorizontalEdges(
+        HevcPictureBuffer source,
+        HevcPictureBuffer destination,
+        HevcPlane plane,
+        int x,
+        int y,
+        int width,
+        int height,
+        bool leftAvailable,
+        bool rightAvailable,
+        in KernelParameters kernel)
+    {
+        int start = x + (leftAvailable ? 0 : 1);
+        int end = x + width - (rightAvailable ? 0 : 1);
+        int count = end - start;
+        if (count <= 0)
+        {
+            return;
+        }
+
+        for (int row = y; row < y + height; row++)
+        {
+            ReadOnlySpan<ushort> sourceRow = source.GetRowSpan(plane, row);
+            ApplyRow<EdgeClassifier>(
+                sourceRow.Slice(start, count),
+                sourceRow.Slice(start - 1, count),
+                sourceRow.Slice(start + 1, count),
+                destination.GetRowSpan(plane, row).Slice(start, count),
+                in kernel);
+        }
+    }
+
+    /// <summary>
+    /// Applies vertical edge offsets within the available upper and lower boundaries.
+    /// </summary>
+    /// <param name="source">The immutable pre-SAO picture.</param>
+    /// <param name="destination">The destination picture.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The block's left coordinate.</param>
+    /// <param name="y">The block's top coordinate.</param>
+    /// <param name="width">The block width.</param>
+    /// <param name="height">The block height.</param>
+    /// <param name="aboveAvailable">Whether the upper neighboring block is available.</param>
+    /// <param name="belowAvailable">Whether the lower neighboring block is available.</param>
+    /// <param name="kernel">The scaled offset state.</param>
+    private static void ApplyVerticalEdges(
+        HevcPictureBuffer source,
+        HevcPictureBuffer destination,
+        HevcPlane plane,
+        int x,
+        int y,
+        int width,
+        int height,
+        bool aboveAvailable,
+        bool belowAvailable,
+        in KernelParameters kernel)
+    {
+        int start = y + (aboveAvailable ? 0 : 1);
+        int end = y + height - (belowAvailable ? 0 : 1);
+        for (int row = start; row < end; row++)
+        {
+            ApplyRow<EdgeClassifier>(
+                source.GetRowSpan(plane, row).Slice(x, width),
+                source.GetRowSpan(plane, row - 1).Slice(x, width),
+                source.GetRowSpan(plane, row + 1).Slice(x, width),
+                destination.GetRowSpan(plane, row).Slice(x, width),
+                in kernel);
+        }
+    }
+
+    /// <summary>
+    /// Applies descending-diagonal edge offsets within the eight resolved block boundaries.
+    /// </summary>
+    /// <param name="source">The immutable pre-SAO picture.</param>
+    /// <param name="destination">The destination picture.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The block's left coordinate.</param>
+    /// <param name="y">The block's top coordinate.</param>
+    /// <param name="width">The block width.</param>
+    /// <param name="height">The block height.</param>
+    /// <param name="leftAvailable">Whether the left neighboring block is available.</param>
+    /// <param name="rightAvailable">Whether the right neighboring block is available.</param>
+    /// <param name="aboveAvailable">Whether the upper neighboring block is available.</param>
+    /// <param name="belowAvailable">Whether the lower neighboring block is available.</param>
+    /// <param name="aboveLeftAvailable">Whether the upper-left neighboring block is available.</param>
+    /// <param name="belowRightAvailable">Whether the lower-right neighboring block is available.</param>
+    /// <param name="kernel">The scaled offset state.</param>
+    private static void ApplyDescendingEdges(
+        HevcPictureBuffer source,
+        HevcPictureBuffer destination,
+        HevcPlane plane,
+        int x,
+        int y,
+        int width,
+        int height,
+        bool leftAvailable,
+        bool rightAvailable,
+        bool aboveAvailable,
+        bool belowAvailable,
+        bool aboveLeftAvailable,
+        bool belowRightAvailable,
+        in KernelParameters kernel)
+    {
+        int commonStart = x + (leftAvailable ? 0 : 1);
+        int commonEnd = x + width - (rightAvailable ? 0 : 1);
+        int lastRow = y + height - 1;
+        for (int row = y; row <= lastRow; row++)
+        {
+            int start = commonStart;
+            int end = commonEnd;
+            if (row == y)
+            {
+                start = aboveLeftAvailable ? x : x + 1;
+                end = aboveAvailable ? commonEnd : x + 1;
+            }
+
+            if (row == lastRow)
+            {
+                start = Math.Max(start, belowAvailable ? commonStart : x + width - 1);
+                end = Math.Min(end, belowRightAvailable ? x + width : x + width - 1);
+            }
+
+            int count = end - start;
+            if (count <= 0)
+            {
+                continue;
+            }
+
+            ApplyRow<EdgeClassifier>(
+                source.GetRowSpan(plane, row).Slice(start, count),
+                source.GetRowSpan(plane, row - 1).Slice(start - 1, count),
+                source.GetRowSpan(plane, row + 1).Slice(start + 1, count),
+                destination.GetRowSpan(plane, row).Slice(start, count),
+                in kernel);
+        }
+    }
+
+    /// <summary>
+    /// Applies ascending-diagonal edge offsets within the eight resolved block boundaries.
+    /// </summary>
+    /// <param name="source">The immutable pre-SAO picture.</param>
+    /// <param name="destination">The destination picture.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="x">The block's left coordinate.</param>
+    /// <param name="y">The block's top coordinate.</param>
+    /// <param name="width">The block width.</param>
+    /// <param name="height">The block height.</param>
+    /// <param name="leftAvailable">Whether the left neighboring block is available.</param>
+    /// <param name="rightAvailable">Whether the right neighboring block is available.</param>
+    /// <param name="aboveAvailable">Whether the upper neighboring block is available.</param>
+    /// <param name="belowAvailable">Whether the lower neighboring block is available.</param>
+    /// <param name="aboveRightAvailable">Whether the upper-right neighboring block is available.</param>
+    /// <param name="belowLeftAvailable">Whether the lower-left neighboring block is available.</param>
+    /// <param name="kernel">The scaled offset state.</param>
+    private static void ApplyAscendingEdges(
+        HevcPictureBuffer source,
+        HevcPictureBuffer destination,
+        HevcPlane plane,
+        int x,
+        int y,
+        int width,
+        int height,
+        bool leftAvailable,
+        bool rightAvailable,
+        bool aboveAvailable,
+        bool belowAvailable,
+        bool aboveRightAvailable,
+        bool belowLeftAvailable,
+        in KernelParameters kernel)
+    {
+        int commonStart = x + (leftAvailable ? 0 : 1);
+        int commonEnd = x + width - (rightAvailable ? 0 : 1);
+        int lastRow = y + height - 1;
+        for (int row = y; row <= lastRow; row++)
+        {
+            int start = commonStart;
+            int end = commonEnd;
+            if (row == y)
+            {
+                start = aboveAvailable ? commonStart : x + width - 1;
+                end = aboveRightAvailable ? x + width : x + width - 1;
+            }
+
+            if (row == lastRow)
+            {
+                start = Math.Max(start, belowLeftAvailable ? x : x + 1);
+                end = Math.Min(end, belowAvailable ? commonEnd : x + 1);
+            }
+
+            int count = end - start;
+            if (count <= 0)
+            {
+                continue;
+            }
+
+            ApplyRow<EdgeClassifier>(
+                source.GetRowSpan(plane, row).Slice(start, count),
+                source.GetRowSpan(plane, row - 1).Slice(start + 1, count),
+                source.GetRowSpan(plane, row + 1).Slice(start - 1, count),
+                destination.GetRowSpan(plane, row).Slice(start, count),
+                in kernel);
+        }
+    }
+
+    /// <summary>
+    /// Applies one closed classifier to a contiguous row range using every accelerated SIMD width before the scalar tail.
+    /// </summary>
+    /// <typeparam name="TClassifier">The band or edge classifier selected before entering the row.</typeparam>
+    /// <param name="current">The current source samples.</param>
+    /// <param name="neighbor0">The first classifier input samples.</param>
+    /// <param name="neighbor1">The second classifier input samples.</param>
+    /// <param name="destination">The destination samples.</param>
+    /// <param name="kernel">The scaled offset and clamp state.</param>
+    private static void ApplyRow<TClassifier>(
+        ReadOnlySpan<ushort> current,
+        ReadOnlySpan<ushort> neighbor0,
+        ReadOnlySpan<ushort> neighbor1,
+        Span<ushort> destination,
+        in KernelParameters kernel)
+        where TClassifier : struct, ISampleClassifier
+    {
+        ref ushort currentBase = ref MemoryMarshal.GetReference(current);
+        ref ushort neighbor0Base = ref MemoryMarshal.GetReference(neighbor0);
+        ref ushort neighbor1Base = ref MemoryMarshal.GetReference(neighbor1);
+        ref ushort destinationBase = ref MemoryMarshal.GetReference(destination);
+        int index = 0;
+
+        // HEVC's exposed 8/10/12-bit profiles keep every sample and scaled offset inside Int16. Signed lanes therefore
+        // provide comparisons, addition, and saturation without the two widening stages an Int32 implementation needs.
+        if (Vector512.IsHardwareAccelerated)
+        {
+            Vector512<short> minimum = Vector512<short>.Zero;
+            Vector512<short> maximum = Vector512.Create(kernel.Maximum);
+            for (; index <= current.Length - Vector512<ushort>.Count; index += Vector512<ushort>.Count)
+            {
+                Vector512<short> value = Vector512.LoadUnsafe(ref currentBase, (nuint)index).AsInt16();
+                Vector512<short> first = TClassifier.UsesNeighbors ? Vector512.LoadUnsafe(ref neighbor0Base, (nuint)index).AsInt16() : default;
+                Vector512<short> second = TClassifier.UsesNeighbors ? Vector512.LoadUnsafe(ref neighbor1Base, (nuint)index).AsInt16() : default;
+                Vector512<short> classes = TClassifier.Classify(value, first, second, in kernel);
+                Vector512<short> filtered = Vector512.Clamp(value + SelectOffset(classes, in kernel), minimum, maximum);
+                filtered.AsUInt16().StoreUnsafe(ref destinationBase, (nuint)index);
+            }
+        }
+
+        if (Vector256.IsHardwareAccelerated)
+        {
+            Vector256<short> minimum = Vector256<short>.Zero;
+            Vector256<short> maximum = Vector256.Create(kernel.Maximum);
+            for (; index <= current.Length - Vector256<ushort>.Count; index += Vector256<ushort>.Count)
+            {
+                Vector256<short> value = Vector256.LoadUnsafe(ref currentBase, (nuint)index).AsInt16();
+                Vector256<short> first = TClassifier.UsesNeighbors ? Vector256.LoadUnsafe(ref neighbor0Base, (nuint)index).AsInt16() : default;
+                Vector256<short> second = TClassifier.UsesNeighbors ? Vector256.LoadUnsafe(ref neighbor1Base, (nuint)index).AsInt16() : default;
+                Vector256<short> classes = TClassifier.Classify(value, first, second, in kernel);
+                Vector256<short> filtered = Vector256.Clamp(value + SelectOffset(classes, in kernel), minimum, maximum);
+                filtered.AsUInt16().StoreUnsafe(ref destinationBase, (nuint)index);
+            }
+        }
+
+        if (Vector128.IsHardwareAccelerated)
+        {
+            Vector128<short> minimum = Vector128<short>.Zero;
+            Vector128<short> maximum = Vector128.Create(kernel.Maximum);
+            for (; index <= current.Length - Vector128<ushort>.Count; index += Vector128<ushort>.Count)
+            {
+                Vector128<short> value = Vector128.LoadUnsafe(ref currentBase, (nuint)index).AsInt16();
+                Vector128<short> first = TClassifier.UsesNeighbors ? Vector128.LoadUnsafe(ref neighbor0Base, (nuint)index).AsInt16() : default;
+                Vector128<short> second = TClassifier.UsesNeighbors ? Vector128.LoadUnsafe(ref neighbor1Base, (nuint)index).AsInt16() : default;
+                Vector128<short> classes = TClassifier.Classify(value, first, second, in kernel);
+                Vector128<short> filtered = Vector128.Clamp(value + SelectOffset(classes, in kernel), minimum, maximum);
+                filtered.AsUInt16().StoreUnsafe(ref destinationBase, (nuint)index);
+            }
+        }
+
+        for (; index < current.Length; index++)
+        {
+            short currentValue = (short)Unsafe.Add(ref currentBase, index);
+            short first = TClassifier.UsesNeighbors ? (short)Unsafe.Add(ref neighbor0Base, index) : default;
+            short second = TClassifier.UsesNeighbors ? (short)Unsafe.Add(ref neighbor1Base, index) : default;
+            int offsetIndex = TClassifier.Classify(currentValue, first, second, in kernel);
+
+            int filtered = Unsafe.Add(ref currentBase, index) + SelectOffset(offsetIndex, in kernel);
+            Unsafe.Add(ref destinationBase, index) = (ushort)Math.Clamp(filtered, 0, kernel.Maximum);
+        }
+    }
+
+    /// <summary>
+    /// Selects one of five signed offsets for thirty-two classifier indices.
+    /// </summary>
+    /// <param name="classes">The zero-based classifier indices.</param>
+    /// <param name="kernel">The five scaled offsets.</param>
+    /// <returns>The selected signed offset in every lane.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static Vector512<short> SelectOffset(Vector512<short> classes, in KernelParameters kernel)
+    {
+        Vector512<short> selected = Vector512<short>.Zero;
+        selected = Vector512.ConditionalSelect(Vector512.Equals(classes, Vector512.Create((short)0)), Vector512.Create(kernel.Offset0), selected);
+        selected = Vector512.ConditionalSelect(Vector512.Equals(classes, Vector512.Create((short)1)), Vector512.Create(kernel.Offset1), selected);
+        selected = Vector512.ConditionalSelect(Vector512.Equals(classes, Vector512.Create((short)2)), Vector512.Create(kernel.Offset2), selected);
+        selected = Vector512.ConditionalSelect(Vector512.Equals(classes, Vector512.Create((short)3)), Vector512.Create(kernel.Offset3), selected);
+        return Vector512.ConditionalSelect(Vector512.Equals(classes, Vector512.Create((short)4)), Vector512.Create(kernel.Offset4), selected);
+    }
+
+    /// <summary>
+    /// Selects one of five signed offsets for sixteen classifier indices.
+    /// </summary>
+    /// <param name="classes">The zero-based classifier indices.</param>
+    /// <param name="kernel">The five scaled offsets.</param>
+    /// <returns>The selected signed offset in every lane.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static Vector256<short> SelectOffset(Vector256<short> classes, in KernelParameters kernel)
+    {
+        Vector256<short> selected = Vector256<short>.Zero;
+        selected = Vector256.ConditionalSelect(Vector256.Equals(classes, Vector256.Create((short)0)), Vector256.Create(kernel.Offset0), selected);
+        selected = Vector256.ConditionalSelect(Vector256.Equals(classes, Vector256.Create((short)1)), Vector256.Create(kernel.Offset1), selected);
+        selected = Vector256.ConditionalSelect(Vector256.Equals(classes, Vector256.Create((short)2)), Vector256.Create(kernel.Offset2), selected);
+        selected = Vector256.ConditionalSelect(Vector256.Equals(classes, Vector256.Create((short)3)), Vector256.Create(kernel.Offset3), selected);
+        return Vector256.ConditionalSelect(Vector256.Equals(classes, Vector256.Create((short)4)), Vector256.Create(kernel.Offset4), selected);
+    }
+
+    /// <summary>
+    /// Selects one of five signed offsets for eight classifier indices.
+    /// </summary>
+    /// <param name="classes">The zero-based classifier indices.</param>
+    /// <param name="kernel">The five scaled offsets.</param>
+    /// <returns>The selected signed offset in every lane.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static Vector128<short> SelectOffset(Vector128<short> classes, in KernelParameters kernel)
+    {
+        Vector128<short> selected = Vector128<short>.Zero;
+        selected = Vector128.ConditionalSelect(Vector128.Equals(classes, Vector128.Create((short)0)), Vector128.Create(kernel.Offset0), selected);
+        selected = Vector128.ConditionalSelect(Vector128.Equals(classes, Vector128.Create((short)1)), Vector128.Create(kernel.Offset1), selected);
+        selected = Vector128.ConditionalSelect(Vector128.Equals(classes, Vector128.Create((short)2)), Vector128.Create(kernel.Offset2), selected);
+        selected = Vector128.ConditionalSelect(Vector128.Equals(classes, Vector128.Create((short)3)), Vector128.Create(kernel.Offset3), selected);
+        return Vector128.ConditionalSelect(Vector128.Equals(classes, Vector128.Create((short)4)), Vector128.Create(kernel.Offset4), selected);
+    }
+
+    /// <summary>
+    /// Selects one of five signed offsets for one classifier index.
+    /// </summary>
+    /// <param name="classification">The zero-based classifier index.</param>
+    /// <param name="kernel">The five scaled offsets.</param>
+    /// <returns>The selected signed offset, or zero for an unmodified class.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static int SelectOffset(int classification, in KernelParameters kernel)
+        => classification switch
+        {
+            0 => kernel.Offset0,
+            1 => kernel.Offset1,
+            2 => kernel.Offset2,
+            3 => kernel.Offset3,
+            4 => kernel.Offset4,
+            _ => 0,
+        };
+
+    /// <summary>
+    /// Classifies samples by one of thirty-two most-significant-value bands.
+    /// </summary>
+    private readonly struct BandClassifier : ISampleClassifier
+    {
+        /// <inheritdoc/>
+        public static bool UsesNeighbors => false;
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector512<short> Classify(
+            Vector512<short> current,
+            Vector512<short> neighbor0,
+            Vector512<short> neighbor1,
+            in KernelParameters kernel)
+            => (Vector512.ShiftRightArithmetic(current, kernel.BandShift) - Vector512.Create(kernel.BandPosition)) & Vector512.Create((short)31);
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector256<short> Classify(
+            Vector256<short> current,
+            Vector256<short> neighbor0,
+            Vector256<short> neighbor1,
+            in KernelParameters kernel)
+            => (Vector256.ShiftRightArithmetic(current, kernel.BandShift) - Vector256.Create(kernel.BandPosition)) & Vector256.Create((short)31);
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector128<short> Classify(
+            Vector128<short> current,
+            Vector128<short> neighbor0,
+            Vector128<short> neighbor1,
+            in KernelParameters kernel)
+            => (Vector128.ShiftRightArithmetic(current, kernel.BandShift) - Vector128.Create(kernel.BandPosition)) & Vector128.Create((short)31);
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int Classify(short current, short neighbor0, short neighbor1, in KernelParameters kernel)
+            => ((current >> kernel.BandShift) - kernel.BandPosition) & 31;
+    }
+
+    /// <summary>
+    /// Classifies samples by the sum of their signs relative to two directional neighbors.
+    /// </summary>
+    private readonly struct EdgeClassifier : ISampleClassifier
+    {
+        /// <inheritdoc/>
+        public static bool UsesNeighbors => true;
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector512<short> Classify(
+            Vector512<short> current,
+            Vector512<short> neighbor0,
+            Vector512<short> neighbor1,
+            in KernelParameters kernel)
+        {
+            Vector512<short> one = Vector512.Create((short)1);
+            Vector512<short> sign0 = (Vector512.GreaterThan(current, neighbor0) & one) - (Vector512.LessThan(current, neighbor0) & one);
+            Vector512<short> sign1 = (Vector512.GreaterThan(current, neighbor1) & one) - (Vector512.LessThan(current, neighbor1) & one);
+            return sign0 + sign1 + Vector512.Create((short)2);
+        }
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector256<short> Classify(
+            Vector256<short> current,
+            Vector256<short> neighbor0,
+            Vector256<short> neighbor1,
+            in KernelParameters kernel)
+        {
+            Vector256<short> one = Vector256.Create((short)1);
+            Vector256<short> sign0 = (Vector256.GreaterThan(current, neighbor0) & one) - (Vector256.LessThan(current, neighbor0) & one);
+            Vector256<short> sign1 = (Vector256.GreaterThan(current, neighbor1) & one) - (Vector256.LessThan(current, neighbor1) & one);
+            return sign0 + sign1 + Vector256.Create((short)2);
+        }
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector128<short> Classify(
+            Vector128<short> current,
+            Vector128<short> neighbor0,
+            Vector128<short> neighbor1,
+            in KernelParameters kernel)
+        {
+            Vector128<short> one = Vector128.Create((short)1);
+            Vector128<short> sign0 = (Vector128.GreaterThan(current, neighbor0) & one) - (Vector128.LessThan(current, neighbor0) & one);
+            Vector128<short> sign1 = (Vector128.GreaterThan(current, neighbor1) & one) - (Vector128.LessThan(current, neighbor1) & one);
+            return sign0 + sign1 + Vector128.Create((short)2);
+        }
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int Classify(short current, short neighbor0, short neighbor1, in KernelParameters kernel)
+            => Math.Sign(current - neighbor0) + Math.Sign(current - neighbor1) + 2;
+    }
+
+    /// <summary>
+    /// Contains one block's scaled offsets and invariant classification values.
+    /// </summary>
+    private readonly struct KernelParameters
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="KernelParameters"/> struct.
+        /// </summary>
+        /// <param name="parameters">The decoded signed offsets.</param>
+        /// <param name="bitDepth">The component sample precision.</param>
+        /// <param name="offsetScaleLog2">The component offset scale.</param>
+        public KernelParameters(in HevcSampleAdaptiveOffsetParameters parameters, int bitDepth, int offsetScaleLog2)
+        {
+            // Range Extensions scales each coded offset once before filtering. Hoisting the shifts here keeps the
+            // classification loops to comparisons, table selection, one addition, and saturation.
+            this.Offset0 = (short)(parameters.Offset0 << offsetScaleLog2);
+            this.Offset1 = (short)(parameters.Offset1 << offsetScaleLog2);
+            this.Offset2 = (short)(parameters.Offset2 << offsetScaleLog2);
+            this.Offset3 = (short)(parameters.Offset3 << offsetScaleLog2);
+            this.Offset4 = (short)(parameters.Offset4 << offsetScaleLog2);
+            this.BandPosition = (short)parameters.BandPosition;
+            this.BandShift = bitDepth - 5;
+            this.Maximum = (short)((1 << bitDepth) - 1);
+        }
+
+        /// <summary>
+        /// Gets the first scaled class offset.
+        /// </summary>
+        public short Offset0 { get; }
+
+        /// <summary>
+        /// Gets the second scaled class offset.
+        /// </summary>
+        public short Offset1 { get; }
+
+        /// <summary>
+        /// Gets the third scaled class offset.
+        /// </summary>
+        public short Offset2 { get; }
+
+        /// <summary>
+        /// Gets the fourth scaled class offset.
+        /// </summary>
+        public short Offset3 { get; }
+
+        /// <summary>
+        /// Gets the fifth scaled class offset.
+        /// </summary>
+        public short Offset4 { get; }
+
+        /// <summary>
+        /// Gets the first active band class.
+        /// </summary>
+        public short BandPosition { get; }
+
+        /// <summary>
+        /// Gets the number of low sample bits discarded to form one of thirty-two band classes.
+        /// </summary>
+        public int BandShift { get; }
+
+        /// <summary>
+        /// Gets the largest component sample value.
+        /// </summary>
+        public short Maximum { get; }
+    }
+}

src/ImageSharp/Formats/Heif/Hevc/HevcSampleAdaptiveOffsetParameters.cs

@@ -0,0 +1,443 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers;
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <summary>
+/// Identifies the HEVC sample-adaptive-offset classifier selected for one component coding-tree block.
+/// </summary>
+internal enum HevcSampleAdaptiveOffsetType : byte
+{
+    /// <summary>
+    /// No sample-adaptive offset is applied.
+    /// </summary>
+    Off,
+
+    /// <summary>
+    /// Samples are classified by their most-significant sample-value band.
+    /// </summary>
+    Band,
+
+    /// <summary>
+    /// Samples are classified by horizontal neighboring samples.
+    /// </summary>
+    EdgeHorizontal,
+
+    /// <summary>
+    /// Samples are classified by vertical neighboring samples.
+    /// </summary>
+    EdgeVertical,
+
+    /// <summary>
+    /// Samples are classified by neighbors on the descending diagonal.
+    /// </summary>
+    EdgeDescending,
+
+    /// <summary>
+    /// Samples are classified by neighbors on the ascending diagonal.
+    /// </summary>
+    EdgeAscending,
+}
+
+/// <summary>
+/// Contains the resolved HEVC sample-adaptive offsets for one component coding-tree block.
+/// </summary>
+internal readonly struct HevcSampleAdaptiveOffsetParameters
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcSampleAdaptiveOffsetParameters"/> struct.
+    /// </summary>
+    /// <param name="type">The sample classifier.</param>
+    /// <param name="bandPosition">The first of four consecutive band classes.</param>
+    /// <param name="offset0">The first band or full-valley offset.</param>
+    /// <param name="offset1">The second band or half-valley offset.</param>
+    /// <param name="offset2">The third band or plain-edge offset.</param>
+    /// <param name="offset3">The fourth band or half-peak offset.</param>
+    /// <param name="offset4">The full-peak offset.</param>
+    public HevcSampleAdaptiveOffsetParameters(
+        HevcSampleAdaptiveOffsetType type,
+        int bandPosition,
+        int offset0,
+        int offset1,
+        int offset2,
+        int offset3,
+        int offset4)
+    {
+        this.Type = type;
+        this.BandPosition = bandPosition;
+        this.Offset0 = offset0;
+        this.Offset1 = offset1;
+        this.Offset2 = offset2;
+        this.Offset3 = offset3;
+        this.Offset4 = offset4;
+    }
+
+    /// <summary>
+    /// Gets the sample classifier.
+    /// </summary>
+    public HevcSampleAdaptiveOffsetType Type { get; }
+
+    /// <summary>
+    /// Gets the first of four consecutive band classes.
+    /// </summary>
+    public int BandPosition { get; }
+
+    /// <summary>
+    /// Gets the first band or full-valley offset.
+    /// </summary>
+    public int Offset0 { get; }
+
+    /// <summary>
+    /// Gets the second band or half-valley offset.
+    /// </summary>
+    public int Offset1 { get; }
+
+    /// <summary>
+    /// Gets the third band or plain-edge offset.
+    /// </summary>
+    public int Offset2 { get; }
+
+    /// <summary>
+    /// Gets the fourth band or half-peak offset.
+    /// </summary>
+    public int Offset3 { get; }
+
+    /// <summary>
+    /// Gets the full-peak offset.
+    /// </summary>
+    public int Offset4 { get; }
+}
+
+/// <summary>
+/// Identifies the slice and tile governing in-loop filtering for one coding-tree block.
+/// </summary>
+internal readonly struct HevcLoopFilterRegion
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcLoopFilterRegion"/> struct.
+    /// </summary>
+    /// <param name="sliceStartAddressInTileScan">The first coding-tree block of the independent slice in tile-scan order.</param>
+    /// <param name="tileIndex">The zero-based tile index.</param>
+    /// <param name="loopFilterAcrossSlicesEnabled">Whether the governing slice permits filtering across its slice boundary.</param>
+    /// <param name="deblockingFilterDisabled">Whether the governing slice disables deblocking.</param>
+    /// <param name="deblockingFilterBetaOffsetDiv2">Half the slice beta-threshold offset.</param>
+    /// <param name="deblockingFilterTcOffsetDiv2">Half the slice clipping-threshold offset.</param>
+    public HevcLoopFilterRegion(
+        int sliceStartAddressInTileScan,
+        int tileIndex,
+        bool loopFilterAcrossSlicesEnabled,
+        bool deblockingFilterDisabled,
+        int deblockingFilterBetaOffsetDiv2,
+        int deblockingFilterTcOffsetDiv2)
+    {
+        this.SliceStartAddressInTileScan = sliceStartAddressInTileScan;
+        this.TileIndex = tileIndex;
+        this.LoopFilterAcrossSlicesEnabled = loopFilterAcrossSlicesEnabled;
+        this.DeblockingFilterDisabled = deblockingFilterDisabled;
+        this.DeblockingFilterBetaOffsetDiv2 = deblockingFilterBetaOffsetDiv2;
+        this.DeblockingFilterTcOffsetDiv2 = deblockingFilterTcOffsetDiv2;
+    }
+
+    /// <summary>
+    /// Gets the first coding-tree block of the independent slice in tile-scan order.
+    /// </summary>
+    public int SliceStartAddressInTileScan { get; }
+
+    /// <summary>
+    /// Gets the zero-based tile index.
+    /// </summary>
+    public int TileIndex { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the governing slice permits filtering across its slice boundary.
+    /// </summary>
+    public bool LoopFilterAcrossSlicesEnabled { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the governing slice disables deblocking.
+    /// </summary>
+    public bool DeblockingFilterDisabled { get; }
+
+    /// <summary>
+    /// Gets half the governing slice's beta-threshold offset.
+    /// </summary>
+    public int DeblockingFilterBetaOffsetDiv2 { get; }
+
+    /// <summary>
+    /// Gets half the governing slice's clipping-threshold offset.
+    /// </summary>
+    public int DeblockingFilterTcOffsetDiv2 { get; }
+}
+
+/// <summary>
+/// Contains the eight coding-tree-block neighbor availability values used by HEVC in-loop filters.
+/// </summary>
+internal readonly struct HevcLoopFilterBoundaryAvailability
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcLoopFilterBoundaryAvailability"/> struct.
+    /// </summary>
+    /// <param name="left">Whether the left block is available.</param>
+    /// <param name="right">Whether the right block is available.</param>
+    /// <param name="above">Whether the block above is available.</param>
+    /// <param name="below">Whether the block below is available.</param>
+    /// <param name="aboveLeft">Whether the upper-left block is available.</param>
+    /// <param name="aboveRight">Whether the upper-right block is available.</param>
+    /// <param name="belowLeft">Whether the lower-left block is available.</param>
+    /// <param name="belowRight">Whether the lower-right block is available.</param>
+    public HevcLoopFilterBoundaryAvailability(
+        bool left,
+        bool right,
+        bool above,
+        bool below,
+        bool aboveLeft,
+        bool aboveRight,
+        bool belowLeft,
+        bool belowRight)
+    {
+        this.Left = left;
+        this.Right = right;
+        this.Above = above;
+        this.Below = below;
+        this.AboveLeft = aboveLeft;
+        this.AboveRight = aboveRight;
+        this.BelowLeft = belowLeft;
+        this.BelowRight = belowRight;
+    }
+
+    /// <summary>
+    /// Gets a value indicating whether the left block is available.
+    /// </summary>
+    public bool Left { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the right block is available.
+    /// </summary>
+    public bool Right { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the block above is available.
+    /// </summary>
+    public bool Above { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the block below is available.
+    /// </summary>
+    public bool Below { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the upper-left block is available.
+    /// </summary>
+    public bool AboveLeft { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the upper-right block is available.
+    /// </summary>
+    public bool AboveRight { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the lower-left block is available.
+    /// </summary>
+    public bool BelowLeft { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether the lower-right block is available.
+    /// </summary>
+    public bool BelowRight { get; }
+}
+
+/// <summary>
+/// Owns resolved sample-adaptive-offset parameters and prediction and filter region identifiers for one picture.
+/// </summary>
+internal sealed class HevcSampleAdaptiveOffsetState : IDisposable
+{
+    /// <summary>
+    /// Whether any decoded component block enables sample-adaptive offset.
+    /// </summary>
+    private bool hasEnabledParameters;
+
+    /// <summary>
+    /// The three component records for every raster-ordered coding-tree block.
+    /// </summary>
+    private readonly IMemoryOwner<HevcSampleAdaptiveOffsetParameters> parameters;
+
+    /// <summary>
+    /// The independent-slice and tile prediction region of every coding-tree block.
+    /// </summary>
+    private readonly IMemoryOwner<int> regions;
+
+    /// <summary>
+    /// The independent-slice and tile filter region of every coding-tree block and color plane.
+    /// </summary>
+    private readonly IMemoryOwner<HevcLoopFilterRegion> loopFilterRegions;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcSampleAdaptiveOffsetState"/> class.
+    /// </summary>
+    /// <param name="configuration">The configuration providing pooled picture state.</param>
+    /// <param name="codingTreeBlockCount">The raster-ordered coding-tree-block count.</param>
+    public HevcSampleAdaptiveOffsetState(Configuration configuration, int codingTreeBlockCount)
+    {
+        this.parameters = configuration.MemoryAllocator.Allocate<HevcSampleAdaptiveOffsetParameters>(codingTreeBlockCount * 3);
+        this.regions = configuration.MemoryAllocator.Allocate<int>(codingTreeBlockCount * 3);
+        this.loopFilterRegions = configuration.MemoryAllocator.Allocate<HevcLoopFilterRegion>(codingTreeBlockCount * 3);
+    }
+
+    /// <summary>
+    /// Gets a value indicating whether any component block enables sample-adaptive offset.
+    /// </summary>
+    public bool HasEnabledParameters => this.hasEnabledParameters;
+
+    /// <summary>
+    /// Gets the resolved component parameters for one coding-tree block.
+    /// </summary>
+    /// <param name="rasterAddress">The raster-scan coding-tree-block address.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <returns>The resolved sample-adaptive-offset parameters.</returns>
+    public HevcSampleAdaptiveOffsetParameters Get(int rasterAddress, HevcPlane plane)
+        => this.parameters.Memory.Span[(rasterAddress * 3) + (int)plane];
+
+    /// <summary>
+    /// Stores resolved component parameters for one coding-tree block.
+    /// </summary>
+    /// <param name="rasterAddress">The raster-scan coding-tree-block address.</param>
+    /// <param name="plane">The component plane.</param>
+    /// <param name="value">The resolved sample-adaptive-offset parameters.</param>
+    public void Set(int rasterAddress, HevcPlane plane, HevcSampleAdaptiveOffsetParameters value)
+    {
+        this.parameters.Memory.Span[(rasterAddress * 3) + (int)plane] = value;
+        this.hasEnabledParameters |= value.Type != HevcSampleAdaptiveOffsetType.Off;
+    }
+
+    /// <summary>
+    /// Gets whether one coding-tree block belongs to the selected prediction region.
+    /// </summary>
+    /// <param name="rasterAddress">The raster-scan coding-tree-block address.</param>
+    /// <param name="plane">The independently coded color plane, or luma for combined-plane coding.</param>
+    /// <param name="regionId">The current independent-slice and tile prediction-region identifier.</param>
+    /// <returns><see langword="true"/> when the block belongs to the region; otherwise, <see langword="false"/>.</returns>
+    public bool IsInRegion(int rasterAddress, HevcPlane plane, int regionId)
+        => this.regions.Memory.Span[(rasterAddress * 3) + (int)plane] == regionId;
+
+    /// <summary>
+    /// Records the prediction region after one coding-tree block's parameters are decoded.
+    /// </summary>
+    /// <param name="rasterAddress">The raster-scan coding-tree-block address.</param>
+    /// <param name="plane">The independently coded color plane, or luma for combined-plane coding.</param>
+    /// <param name="regionId">The positive prediction-region identifier.</param>
+    public void SetRegion(int rasterAddress, HevcPlane plane, int regionId)
+        => this.regions.Memory.Span[(rasterAddress * 3) + (int)plane] = regionId;
+
+    /// <summary>
+    /// Records the in-loop filter region for one coding-tree block.
+    /// </summary>
+    /// <param name="rasterAddress">The raster-scan coding-tree-block address.</param>
+    /// <param name="plane">The independently coded color plane, or luma for combined-plane coding.</param>
+    /// <param name="value">The governing independent-slice and tile state.</param>
+    public void SetLoopFilterRegion(int rasterAddress, HevcPlane plane, HevcLoopFilterRegion value)
+        => this.loopFilterRegions.Memory.Span[(rasterAddress * 3) + (int)plane] = value;
+
+    /// <summary>
+    /// Derives the picture, slice, and tile boundary availability used by the in-loop filters for one coding-tree block.
+    /// </summary>
+    /// <param name="rasterAddress">The raster-scan coding-tree-block address.</param>
+    /// <param name="plane">The independently coded color plane, or luma for combined-plane coding.</param>
+    /// <param name="pictureWidth">The picture width in coding-tree blocks.</param>
+    /// <param name="pictureHeight">The picture height in coding-tree blocks.</param>
+    /// <param name="loopFilterAcrossTilesEnabled">Whether the picture permits filtering across tile boundaries.</param>
+    /// <returns>The availability of all eight neighboring coding-tree blocks.</returns>
+    public HevcLoopFilterBoundaryAvailability GetLoopFilterBoundaryAvailability(
+        int rasterAddress,
+        HevcPlane plane,
+        int pictureWidth,
+        int pictureHeight,
+        bool loopFilterAcrossTilesEnabled)
+    {
+        int x = rasterAddress % pictureWidth;
+        int y = rasterAddress / pictureWidth;
+        HevcLoopFilterRegion current = this.GetLoopFilterRegion(rasterAddress, plane);
+
+        // H.265 assigns left, above, and upper-left boundaries to the current slice, while right, below, and
+        // lower-right boundaries belong to the neighboring slice. This asymmetry makes filtering independent of CTB order.
+        bool left = x > 0
+            && IsLoopFilterNeighborAvailable(current, this.GetLoopFilterRegion(rasterAddress - 1, plane), true, loopFilterAcrossTilesEnabled);
+        bool right = x + 1 < pictureWidth
+            && IsLoopFilterNeighborAvailable(current, this.GetLoopFilterRegion(rasterAddress + 1, plane), false, loopFilterAcrossTilesEnabled);
+        bool above = y > 0
+            && IsLoopFilterNeighborAvailable(current, this.GetLoopFilterRegion(rasterAddress - pictureWidth, plane), true, loopFilterAcrossTilesEnabled);
+        bool below = y + 1 < pictureHeight
+            && IsLoopFilterNeighborAvailable(current, this.GetLoopFilterRegion(rasterAddress + pictureWidth, plane), false, loopFilterAcrossTilesEnabled);
+        bool aboveLeft = x > 0 && y > 0
+            && IsLoopFilterNeighborAvailable(current, this.GetLoopFilterRegion(rasterAddress - pictureWidth - 1, plane), true, loopFilterAcrossTilesEnabled);
+        bool belowRight = x + 1 < pictureWidth && y + 1 < pictureHeight
+            && IsLoopFilterNeighborAvailable(current, this.GetLoopFilterRegion(rasterAddress + pictureWidth + 1, plane), false, loopFilterAcrossTilesEnabled);
+
+        // The crossed diagonals do not have a fixed owner in raster order. The later independent slice owns the
+        // boundary flag, which is identified by its greater tile-scan start address.
+        bool aboveRight = x + 1 < pictureWidth && y > 0
+            && IsLoopFilterDiagonalAvailable(current, this.GetLoopFilterRegion(rasterAddress - pictureWidth + 1, plane), loopFilterAcrossTilesEnabled);
+        bool belowLeft = x > 0 && y + 1 < pictureHeight
+            && IsLoopFilterDiagonalAvailable(current, this.GetLoopFilterRegion(rasterAddress + pictureWidth - 1, plane), loopFilterAcrossTilesEnabled);
+
+        return new HevcLoopFilterBoundaryAvailability(left, right, above, below, aboveLeft, aboveRight, belowLeft, belowRight);
+    }
+
+    /// <summary>
+    /// Gets the retained in-loop filter region for one coding-tree block.
+    /// </summary>
+    /// <param name="rasterAddress">The raster-scan coding-tree-block address.</param>
+    /// <param name="plane">The independently coded color plane, or luma for combined-plane coding.</param>
+    /// <returns>The retained slice and tile state.</returns>
+    public HevcLoopFilterRegion GetLoopFilterRegion(int rasterAddress, HevcPlane plane)
+        => this.loopFilterRegions.Memory.Span[(rasterAddress * 3) + (int)plane];
+
+    /// <summary>
+    /// Determines availability across a boundary with a direction-selected slice owner.
+    /// </summary>
+    /// <param name="current">The current block's region.</param>
+    /// <param name="neighbor">The neighboring block's region.</param>
+    /// <param name="currentOwnsSliceBoundary">Whether the current slice controls a boundary between different slices.</param>
+    /// <param name="loopFilterAcrossTilesEnabled">Whether tile boundaries permit filtering.</param>
+    /// <returns><see langword="true"/> when both slice and tile rules permit filtering.</returns>
+    private static bool IsLoopFilterNeighborAvailable(
+        HevcLoopFilterRegion current,
+        HevcLoopFilterRegion neighbor,
+        bool currentOwnsSliceBoundary,
+        bool loopFilterAcrossTilesEnabled)
+    {
+        bool sameSlice = current.SliceStartAddressInTileScan == neighbor.SliceStartAddressInTileScan;
+        bool sliceAvailable = sameSlice
+            || (currentOwnsSliceBoundary ? current.LoopFilterAcrossSlicesEnabled : neighbor.LoopFilterAcrossSlicesEnabled);
+
+        return sliceAvailable && (loopFilterAcrossTilesEnabled || current.TileIndex == neighbor.TileIndex);
+    }
+
+    /// <summary>
+    /// Determines availability across a crossed-diagonal boundary using the later slice as its owner.
+    /// </summary>
+    /// <param name="current">The current block's region.</param>
+    /// <param name="neighbor">The diagonally neighboring block's region.</param>
+    /// <param name="loopFilterAcrossTilesEnabled">Whether tile boundaries permit filtering.</param>
+    /// <returns><see langword="true"/> when both slice and tile rules permit filtering.</returns>
+    private static bool IsLoopFilterDiagonalAvailable(
+        HevcLoopFilterRegion current,
+        HevcLoopFilterRegion neighbor,
+        bool loopFilterAcrossTilesEnabled)
+    {
+        bool currentOwnsSliceBoundary = current.SliceStartAddressInTileScan > neighbor.SliceStartAddressInTileScan;
+        return IsLoopFilterNeighborAvailable(current, neighbor, currentOwnsSliceBoundary, loopFilterAcrossTilesEnabled);
+    }
+
+    /// <summary>
+    /// Releases the pooled sample-adaptive-offset picture state.
+    /// </summary>
+    public void Dispose()
+    {
+        this.loopFilterRegions.Dispose();
+        this.regions.Dispose();
+        this.parameters.Dispose();
+    }
+}

src/ImageSharp/Formats/Heif/Hevc/HevcSliceSegmentHeader.cs

@@ -8,6 +8,11 @@ namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
 /// </summary>
 internal sealed class HevcSliceSegmentHeader
 {
+    /// <summary>
+    /// The decoded-byte lengths preceding each tile or wavefront entropy entry point.
+    /// </summary>
+    private int[] entryPointOffsets = [];
+
     /// <summary>
     /// Initializes a new instance of the <see cref="HevcSliceSegmentHeader"/> class.
     /// </summary>
@@ -119,14 +124,26 @@ internal sealed class HevcSliceSegmentHeader
 
         int availableEncodedData = nalUnit.EncodedPayloadLength - encodedHeaderLength;
         int cumulativeEntryPointOffset = 0;
-        foreach (int entryPointOffset in this.EntryPointOffsets)
+        int previousDecodedBoundary = this.HeaderLength;
+        int[] entryPointOffsets = this.entryPointOffsets;
+        for (int index = 0; index < entryPointOffsets.Length; index++)
         {
+            int entryPointOffset = entryPointOffsets[index];
             if (cumulativeEntryPointOffset > availableEncodedData - entryPointOffset)
             {
                 throw new InvalidImageContentException("The HEVC slice entry point extends beyond its NAL unit.");
             }
 
             cumulativeEntryPointOffset += entryPointOffset;
+            int encodedBoundary = encodedHeaderLength + cumulativeEntryPointOffset;
+            int decodedBoundary = GetDecodedPayloadOffset(
+                encodedBoundary,
+                nalUnit.EmulationPreventionBytePositions.Span);
+
+            // entry_point_offset_minus1 counts encoded NAL bytes. The entropy decoder consumes the de-escaped RBSP,
+            // so each retained substream length must exclude prevention bytes from its own encoded interval.
+            entryPointOffsets[index] = decodedBoundary - previousDecodedBoundary;
+            previousDecodedBoundary = decodedBoundary;
         }
     }
 
@@ -216,9 +233,14 @@ internal sealed class HevcSliceSegmentHeader
     public bool? LoopFilterAcrossSlicesEnabled { get; private set; }
 
     /// <summary>
-    /// Gets the encoded-byte lengths that separate tile or wavefront entropy substreams after the first substream.
+    /// Gets the decoded-byte lengths that separate tile or wavefront entropy substreams after the first substream.
+    /// </summary>
+    public IReadOnlyList<int> EntryPointOffsets => this.entryPointOffsets;
+
+    /// <summary>
+    /// Gets the number of independently initialized tile or wavefront entropy substreams in this slice segment.
     /// </summary>
-    public IReadOnlyList<int> EntryPointOffsets { get; private set; } = Array.Empty<int>();
+    public int EntropySubstreamCount => this.entryPointOffsets.Length + 1;
 
     /// <summary>
     /// Gets the slice-header length in decoded raw-byte-sequence payload bytes.
@@ -230,6 +252,27 @@ internal sealed class HevcSliceSegmentHeader
     /// </summary>
     public ReadOnlyMemory<byte> SliceData { get; }
 
+    /// <summary>
+    /// Gets one bounded entropy substream in slice coding order.
+    /// </summary>
+    /// <param name="index">The zero-based entropy-substream index.</param>
+    /// <returns>The decoded raw-byte-sequence payload bytes belonging to the selected substream.</returns>
+    public ReadOnlyMemory<byte> GetEntropySubstream(int index)
+    {
+        DebugGuard.MustBeBetweenOrEqualTo(index, 0, this.entryPointOffsets.Length, nameof(index));
+        int offset = 0;
+        for (int precedingIndex = 0; precedingIndex < index; precedingIndex++)
+        {
+            offset += this.entryPointOffsets[precedingIndex];
+        }
+
+        int length = index < this.entryPointOffsets.Length
+            ? this.entryPointOffsets[index]
+            : this.SliceData.Length - offset;
+
+        return this.SliceData.Slice(offset, length);
+    }
+
     /// <summary>
     /// Reads fields carried only by an independent slice-segment header.
     /// </summary>
@@ -398,7 +441,7 @@ internal sealed class HevcSliceSegmentHeader
             entryPointOffsets[entryPoint] = (int)entryPointOffsetMinusOne + 1;
         }
 
-        this.EntryPointOffsets = entryPointOffsets;
+        this.entryPointOffsets = entryPointOffsets;
     }
 
     /// <summary>
@@ -424,4 +467,28 @@ internal sealed class HevcSliceSegmentHeader
 
         return encodedOffset;
     }
+
+    /// <summary>
+    /// Converts an encoded-payload byte boundary to its corresponding RBSP boundary.
+    /// </summary>
+    /// <param name="encodedOffset">The encoded byte-sequence payload offset.</param>
+    /// <param name="emulationPreventionBytePositions">The removed encoded-payload byte positions.</param>
+    /// <returns>The decoded raw-byte-sequence payload offset at the same syntax boundary.</returns>
+    private static int GetDecodedPayloadOffset(
+        int encodedOffset,
+        ReadOnlySpan<int> emulationPreventionBytePositions)
+    {
+        int decodedOffset = encodedOffset;
+        foreach (int preventionBytePosition in emulationPreventionBytePositions)
+        {
+            if (preventionBytePosition >= encodedOffset)
+            {
+                break;
+            }
+
+            decodedOffset--;
+        }
+
+        return decodedOffset;
+    }
 }

src/ImageSharp/Formats/Heif/Hevc/HevcTileLayout.cs

@@ -0,0 +1,196 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <summary>
+/// Maps HEVC coding-tree blocks between picture raster order and tile-scan order.
+/// </summary>
+internal readonly struct HevcTileLayout
+{
+    /// <summary>
+    /// The tile widths in coding-tree blocks.
+    /// </summary>
+    private readonly IReadOnlyList<int> columnWidths;
+
+    /// <summary>
+    /// The tile heights in coding-tree blocks.
+    /// </summary>
+    private readonly IReadOnlyList<int> rowHeights;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcTileLayout"/> struct.
+    /// </summary>
+    /// <param name="pictureParameterSet">The picture tile geometry.</param>
+    public HevcTileLayout(HevcPictureParameterSet pictureParameterSet)
+        : this(pictureParameterSet.TileColumnWidths, pictureParameterSet.TileRowHeights)
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcTileLayout"/> struct from validated tile dimensions.
+    /// </summary>
+    /// <param name="columnWidths">The tile-column widths in coding-tree blocks.</param>
+    /// <param name="rowHeights">The tile-row heights in coding-tree blocks.</param>
+    public HevcTileLayout(IReadOnlyList<int> columnWidths, IReadOnlyList<int> rowHeights)
+    {
+        this.columnWidths = columnWidths;
+        this.rowHeights = rowHeights;
+        this.ColumnCount = this.columnWidths.Count;
+        this.RowCount = this.rowHeights.Count;
+        this.Width = Sum(this.columnWidths);
+        this.Height = Sum(this.rowHeights);
+    }
+
+    /// <summary>
+    /// Gets the number of tile columns.
+    /// </summary>
+    public int ColumnCount { get; }
+
+    /// <summary>
+    /// Gets the number of tile rows.
+    /// </summary>
+    public int RowCount { get; }
+
+    /// <summary>
+    /// Gets the picture width in coding-tree blocks.
+    /// </summary>
+    public int Width { get; }
+
+    /// <summary>
+    /// Gets the picture height in coding-tree blocks.
+    /// </summary>
+    public int Height { get; }
+
+    /// <summary>
+    /// Gets the number of tiles in the picture.
+    /// </summary>
+    public int TileCount => this.ColumnCount * this.RowCount;
+
+    /// <summary>
+    /// Converts a picture raster-scan address to tile-scan order.
+    /// </summary>
+    /// <param name="rasterAddress">The raster-scan coding-tree-block address.</param>
+    /// <returns>The corresponding tile-scan address.</returns>
+    public int GetTileScanAddress(int rasterAddress)
+    {
+        int x = rasterAddress % this.Width;
+        int y = rasterAddress / this.Width;
+        this.FindTile(x, y, out int tileColumn, out int tileRow, out int tileStartX, out int tileStartY);
+        int address = 0;
+        for (int row = 0; row < tileRow; row++)
+        {
+            address += this.rowHeights[row] * this.Width;
+        }
+
+        for (int column = 0; column < tileColumn; column++)
+        {
+            address += this.columnWidths[column] * this.rowHeights[tileRow];
+        }
+
+        return address + ((y - tileStartY) * this.columnWidths[tileColumn]) + x - tileStartX;
+    }
+
+    /// <summary>
+    /// Converts a tile-scan coding-tree-block address to picture raster order.
+    /// </summary>
+    /// <param name="tileScanAddress">The tile-scan address.</param>
+    /// <returns>The corresponding raster-scan address.</returns>
+    public int GetRasterAddress(int tileScanAddress)
+    {
+        int remaining = tileScanAddress;
+        int tileStartY = 0;
+        for (int tileRow = 0; tileRow < this.RowCount; tileRow++)
+        {
+            int tileStartX = 0;
+            for (int tileColumn = 0; tileColumn < this.ColumnCount; tileColumn++)
+            {
+                int tileWidth = this.columnWidths[tileColumn];
+                int tileHeight = this.rowHeights[tileRow];
+                int tileArea = tileWidth * tileHeight;
+                if (remaining < tileArea)
+                {
+                    int x = tileStartX + (remaining % tileWidth);
+                    int y = tileStartY + (remaining / tileWidth);
+                    return (y * this.Width) + x;
+                }
+
+                remaining -= tileArea;
+                tileStartX += tileWidth;
+            }
+
+            tileStartY += this.rowHeights[tileRow];
+        }
+
+        return this.Width * this.Height;
+    }
+
+    /// <summary>
+    /// Gets the tile and tile-local position of one raster-scan coding-tree block.
+    /// </summary>
+    /// <param name="rasterAddress">The raster-scan address.</param>
+    /// <param name="tileIndex">The zero-based tile index.</param>
+    /// <param name="columnInTile">The horizontal coding-tree-block offset within the tile.</param>
+    /// <param name="rowInTile">The vertical coding-tree-block offset within the tile.</param>
+    /// <param name="tileWidth">The tile width in coding-tree blocks.</param>
+    /// <param name="tileHeight">The tile height in coding-tree blocks.</param>
+    public void GetTilePosition(
+        int rasterAddress,
+        out int tileIndex,
+        out int columnInTile,
+        out int rowInTile,
+        out int tileWidth,
+        out int tileHeight)
+    {
+        int x = rasterAddress % this.Width;
+        int y = rasterAddress / this.Width;
+        this.FindTile(x, y, out int tileColumn, out int tileRow, out int tileStartX, out int tileStartY);
+        tileIndex = (tileRow * this.ColumnCount) + tileColumn;
+        columnInTile = x - tileStartX;
+        rowInTile = y - tileStartY;
+        tileWidth = this.columnWidths[tileColumn];
+        tileHeight = this.rowHeights[tileRow];
+    }
+
+    /// <summary>
+    /// Locates the tile containing one coding-tree-block coordinate.
+    /// </summary>
+    /// <param name="x">The raster coding-tree-block X coordinate.</param>
+    /// <param name="y">The raster coding-tree-block Y coordinate.</param>
+    /// <param name="tileColumn">The containing tile column.</param>
+    /// <param name="tileRow">The containing tile row.</param>
+    /// <param name="tileStartX">The containing tile's left coding-tree-block coordinate.</param>
+    /// <param name="tileStartY">The containing tile's top coding-tree-block coordinate.</param>
+    private void FindTile(int x, int y, out int tileColumn, out int tileRow, out int tileStartX, out int tileStartY)
+    {
+        tileStartX = 0;
+        tileColumn = 0;
+        while (x >= tileStartX + this.columnWidths[tileColumn])
+        {
+            tileStartX += this.columnWidths[tileColumn++];
+        }
+
+        tileStartY = 0;
+        tileRow = 0;
+        while (y >= tileStartY + this.rowHeights[tileRow])
+        {
+            tileStartY += this.rowHeights[tileRow++];
+        }
+    }
+
+    /// <summary>
+    /// Sums one complete tile dimension.
+    /// </summary>
+    /// <param name="values">The tile widths or heights.</param>
+    /// <returns>The complete picture dimension in coding-tree blocks.</returns>
+    private static int Sum(IReadOnlyList<int> values)
+    {
+        int sum = 0;
+        foreach (int value in values)
+        {
+            sum += value;
+        }
+
+        return sum;
+    }
+}

src/ImageSharp/Formats/Heif/Hevc/HevcTransformComponentGeometry.cs

@@ -0,0 +1,59 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <summary>
+/// Describes one component rectangle within an HEVC transform-tree node.
+/// </summary>
+internal readonly struct HevcTransformComponentGeometry
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcTransformComponentGeometry"/> struct.
+    /// </summary>
+    /// <param name="x">The component rectangle left coordinate.</param>
+    /// <param name="y">The component rectangle top coordinate.</param>
+    /// <param name="width">The component rectangle width.</param>
+    /// <param name="height">The component rectangle height.</param>
+    /// <param name="process">Whether this transform-tree section owns the component rectangle.</param>
+    /// <param name="processesAllQuadrants">Whether every child section owns a distinct component rectangle.</param>
+    public HevcTransformComponentGeometry(int x, int y, int width, int height, bool process, bool processesAllQuadrants)
+    {
+        this.X = x;
+        this.Y = y;
+        this.Width = width;
+        this.Height = height;
+        this.Process = process;
+        this.ProcessesAllQuadrants = processesAllQuadrants;
+    }
+
+    /// <summary>
+    /// Gets the component rectangle left coordinate.
+    /// </summary>
+    public int X { get; }
+
+    /// <summary>
+    /// Gets the component rectangle top coordinate.
+    /// </summary>
+    public int Y { get; }
+
+    /// <summary>
+    /// Gets the component rectangle width.
+    /// </summary>
+    public int Width { get; }
+
+    /// <summary>
+    /// Gets the component rectangle height.
+    /// </summary>
+    public int Height { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether this transform-tree section owns the component rectangle.
+    /// </summary>
+    public bool Process { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether each child section owns a distinct component rectangle.
+    /// </summary>
+    public bool ProcessesAllQuadrants { get; }
+}

src/ImageSharp/Formats/Heif/Hevc/HevcTransformUnitGeometry.cs

@@ -0,0 +1,158 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+/// <summary>
+/// Maps one luma transform-tree node to its primary and subsampled component rectangles.
+/// </summary>
+internal readonly struct HevcTransformUnitGeometry
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HevcTransformUnitGeometry"/> struct.
+    /// </summary>
+    /// <param name="log2LumaSize">The base-two logarithm of the luma transform-node side.</param>
+    /// <param name="primaryPlane">The primary plane coded with luma syntax.</param>
+    /// <param name="primary">The primary component rectangle.</param>
+    /// <param name="chromaBlue">The blue-difference chroma rectangle.</param>
+    /// <param name="chromaRed">The red-difference chroma rectangle.</param>
+    /// <param name="hasCombinedChroma">Whether chroma syntax accompanies the primary luma syntax.</param>
+    private HevcTransformUnitGeometry(
+        int log2LumaSize,
+        HevcPlane primaryPlane,
+        HevcTransformComponentGeometry primary,
+        HevcTransformComponentGeometry chromaBlue,
+        HevcTransformComponentGeometry chromaRed,
+        bool hasCombinedChroma)
+    {
+        this.Log2LumaSize = log2LumaSize;
+        this.PrimaryPlane = primaryPlane;
+        this.Primary = primary;
+        this.ChromaBlue = chromaBlue;
+        this.ChromaRed = chromaRed;
+        this.HasCombinedChroma = hasCombinedChroma;
+    }
+
+    /// <summary>
+    /// Gets the base-two logarithm of the luma transform-node side.
+    /// </summary>
+    public int Log2LumaSize { get; }
+
+    /// <summary>
+    /// Gets the plane coded with luma transform syntax.
+    /// </summary>
+    public HevcPlane PrimaryPlane { get; }
+
+    /// <summary>
+    /// Gets the primary component rectangle.
+    /// </summary>
+    public HevcTransformComponentGeometry Primary { get; }
+
+    /// <summary>
+    /// Gets the blue-difference chroma rectangle.
+    /// </summary>
+    public HevcTransformComponentGeometry ChromaBlue { get; }
+
+    /// <summary>
+    /// Gets the red-difference chroma rectangle.
+    /// </summary>
+    public HevcTransformComponentGeometry ChromaRed { get; }
+
+    /// <summary>
+    /// Gets a value indicating whether combined chroma syntax accompanies the primary luma syntax.
+    /// </summary>
+    public bool HasCombinedChroma { get; }
+
+    /// <summary>
+    /// Creates the root component geometry for one coding unit.
+    /// </summary>
+    /// <param name="x">The coding-unit left luma coordinate.</param>
+    /// <param name="y">The coding-unit top luma coordinate.</param>
+    /// <param name="log2Size">The base-two logarithm of the coding-unit side.</param>
+    /// <param name="chromaFormat">The sequence chroma-format identifier.</param>
+    /// <param name="separateColorPlane">Whether each 4:4:4 component is coded as an independent color plane.</param>
+    /// <param name="colorPlaneIndex">The selected separate-color plane, or zero for combined coding.</param>
+    /// <returns>The root transform-unit geometry.</returns>
+    public static HevcTransformUnitGeometry CreateRoot(
+        int x,
+        int y,
+        int log2Size,
+        byte chromaFormat,
+        bool separateColorPlane,
+        int colorPlaneIndex)
+    {
+        int size = 1 << log2Size;
+        HevcPlane primaryPlane = separateColorPlane ? (HevcPlane)colorPlaneIndex : HevcPlane.Y;
+        HevcTransformComponentGeometry primary = new(x, y, size, size, true, true);
+        if (chromaFormat == 0 || separateColorPlane)
+        {
+            return new HevcTransformUnitGeometry(log2Size, primaryPlane, primary, default, default, false);
+        }
+
+        int subsamplingX = chromaFormat is 1 or 2 ? 1 : 0;
+        int subsamplingY = chromaFormat == 1 ? 1 : 0;
+        HevcTransformComponentGeometry chroma = new(
+            x >> subsamplingX,
+            y >> subsamplingY,
+            size >> subsamplingX,
+            size >> subsamplingY,
+            true,
+            true);
+
+        return new HevcTransformUnitGeometry(log2Size, primaryPlane, primary, chroma, chroma, true);
+    }
+
+    /// <summary>
+    /// Creates one of the four Z-ordered child transform nodes.
+    /// </summary>
+    /// <param name="section">The child section from zero through three.</param>
+    /// <returns>The selected child geometry.</returns>
+    public HevcTransformUnitGeometry CreateChild(int section)
+        => new(
+            this.Log2LumaSize - 1,
+            this.PrimaryPlane,
+            SplitComponent(this.Primary, section),
+            SplitComponent(this.ChromaBlue, section),
+            SplitComponent(this.ChromaRed, section),
+            this.HasCombinedChroma);
+
+    /// <summary>
+    /// Splits one component rectangle while retaining sub-minimum chroma at the owning parent level.
+    /// </summary>
+    /// <param name="parent">The parent component rectangle.</param>
+    /// <param name="section">The luma child section from zero through three.</param>
+    /// <returns>The component rectangle visible from the selected child.</returns>
+    private static HevcTransformComponentGeometry SplitComponent(HevcTransformComponentGeometry parent, int section)
+    {
+        if (!parent.Process || parent.Width == 0)
+        {
+            return default;
+        }
+
+        int width = parent.Width >> 1;
+        int height = parent.Height >> 1;
+        int sampleCount = width * height;
+        if ((width < 4 || height < 4) && sampleCount < 16)
+        {
+            // A component transform cannot be smaller than four by four. Its parent rectangle is associated with
+            // the final luma quadrant so CBF and coefficient syntax are consumed exactly once.
+            return new HevcTransformComponentGeometry(parent.X, parent.Y, parent.Width, parent.Height, section == 3, false);
+        }
+
+        if (width < 4)
+        {
+            width = 4;
+            height = sampleCount / width;
+        }
+        else if (height < 4)
+        {
+            height = 4;
+            width = sampleCount / height;
+        }
+
+        int columns = parent.Width / width;
+        int x = parent.X + ((section % columns) * width);
+        int y = parent.Y + ((section / columns) * height);
+        return new HevcTransformComponentGeometry(x, y, width, height, true, true);
+    }
+}

tests/ImageSharp.Tests/Formats/Heif/Hevc/HevcCabacDecoderTests.cs

@@ -0,0 +1,52 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+namespace SixLabors.ImageSharp.Tests.Formats.Heif.Hevc;
+
+/// <summary>
+/// Verifies HEVC arithmetic-decoder suspension and restart around pulse-code-modulated coding units.
+/// </summary>
+[Trait("Format", "Heic")]
+public class HevcCabacDecoderTests
+{
+    /// <summary>
+    /// Verifies that PCM samples begin after the terminating arithmetic bytes and that arithmetic decoding resumes after the raw payload.
+    /// </summary>
+    [Fact]
+    public void PcmPayloadSuspendsAndRestartsArithmeticDecoding()
+    {
+        ReadOnlySpan<byte> data = [0xFF, 0xFF, 0xAB, 0xFF, 0xFF];
+        HevcCabacDecoder decoder = new(data);
+
+        Assert.True(decoder.ReadPcmFlag());
+        Assert.Equal((ushort)0xA, decoder.ReadPcmSample(4));
+        Assert.Equal((ushort)0xB, decoder.ReadPcmSample(4));
+
+        decoder.RestartAfterPcm();
+
+        Assert.True(decoder.ReadTerminate());
+    }
+
+    /// <summary>
+    /// Verifies that a PCM sample cannot read beyond its bounded entropy substream.
+    /// </summary>
+    [Fact]
+    public void PcmPayloadRejectsTruncatedSample()
+    {
+        Assert.Throws<InvalidImageContentException>(ReadTruncatedPcmSample);
+    }
+
+    /// <summary>
+    /// Attempts to read a sample wider than the remaining raw PCM payload.
+    /// </summary>
+    private static void ReadTruncatedPcmSample()
+    {
+        ReadOnlySpan<byte> data = [0xFF, 0xFF, 0x80];
+        HevcCabacDecoder decoder = new(data);
+
+        Assert.True(decoder.ReadPcmFlag());
+        decoder.ReadPcmSample(16);
+    }
+}

tests/ImageSharp.Tests/Formats/Heif/Hevc/HevcResidualReconstructorTests.cs

@@ -175,6 +175,39 @@ public class HevcResidualReconstructorTests
         Assert.Equal(HevcResidualDpcmMode.Vertical, HevcResidualReconstructor.GetImplicitResidualDpcmMode(26, true));
     }
 
+    /// <summary>
+    /// Compares cross-component residual prediction with the scalar signed-precision oracle across SIMD widths and a tail.
+    /// </summary>
+    /// <param name="bitDepthDifference">The luma precision minus the chroma precision.</param>
+    [Theory]
+    [InlineData(-2)]
+    [InlineData(0)]
+    [InlineData(2)]
+    public void CrossComponentPredictionMatchesScalarOracle(int bitDepthDifference)
+    {
+        const int sampleCount = 257;
+        const int alpha = -8;
+        int[] luma = new int[sampleCount];
+        int[] actual = new int[sampleCount];
+        int[] expected = new int[sampleCount];
+        for (int index = 0; index < sampleCount; index++)
+        {
+            luma[index] = (((index * 7919) + 1229) & 65535) - 32768;
+            actual[index] = (((index * 4099) + 811) & 65535) - 32768;
+            expected[index] = actual[index];
+        }
+
+        for (int index = 0; index < sampleCount; index++)
+        {
+            int adjustedLuma = bitDepthDifference >= 0 ? luma[index] >> bitDepthDifference : luma[index] << -bitDepthDifference;
+            expected[index] = Math.Clamp(expected[index] + ((alpha * adjustedLuma) >> 3), short.MinValue, short.MaxValue);
+        }
+
+        HevcResidualReconstructor.ApplyCrossComponentPrediction(luma, actual, sampleCount, alpha, bitDepthDifference);
+
+        Assert.True(expected.AsSpan().SequenceEqual(actual));
+    }
+
     /// <summary>
     /// Applies the normative transform-skip normalization as a scalar test oracle.
     /// </summary>

tests/ImageSharp.Tests/Formats/Heif/Hevc/HevcTileLayoutTests.cs

@@ -0,0 +1,65 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+namespace SixLabors.ImageSharp.Tests.Formats.Heif.Hevc;
+
+/// <summary>
+/// Verifies HEVC coding-tree-block mappings for unequal tile dimensions.
+/// </summary>
+[Trait("Format", "Heic")]
+public class HevcTileLayoutTests
+{
+    /// <summary>
+    /// Verifies the normative tile-row, tile-column, and in-tile raster traversal order.
+    /// </summary>
+    [Fact]
+    public void MapsEveryAddressBetweenRasterAndTileScanOrder()
+    {
+        HevcTileLayout layout = new(new[] { 2, 1 }, new[] { 1, 2 });
+
+        ReadOnlySpan<int> expectedRasterAddresses = [0, 1, 2, 3, 4, 6, 7, 5, 8];
+        for (int tileScanAddress = 0; tileScanAddress < expectedRasterAddresses.Length; tileScanAddress++)
+        {
+            int rasterAddress = expectedRasterAddresses[tileScanAddress];
+            Assert.Equal(rasterAddress, layout.GetRasterAddress(tileScanAddress));
+            Assert.Equal(tileScanAddress, layout.GetTileScanAddress(rasterAddress));
+        }
+    }
+
+    /// <summary>
+    /// Verifies tile identity, local coordinates, and dimensions on both sides of each tile boundary.
+    /// </summary>
+    [Theory]
+    [InlineData(0, 0, 0, 0, 2, 1)]
+    [InlineData(2, 1, 0, 0, 1, 1)]
+    [InlineData(3, 2, 0, 0, 2, 2)]
+    [InlineData(7, 2, 1, 1, 2, 2)]
+    [InlineData(5, 3, 0, 0, 1, 2)]
+    [InlineData(8, 3, 0, 1, 1, 2)]
+    public void ResolvesTileLocalPosition(
+        int rasterAddress,
+        int expectedTileIndex,
+        int expectedColumn,
+        int expectedRow,
+        int expectedWidth,
+        int expectedHeight)
+    {
+        HevcTileLayout layout = new(new[] { 2, 1 }, new[] { 1, 2 });
+
+        layout.GetTilePosition(
+            rasterAddress,
+            out int tileIndex,
+            out int column,
+            out int row,
+            out int width,
+            out int height);
+
+        Assert.Equal(expectedTileIndex, tileIndex);
+        Assert.Equal(expectedColumn, column);
+        Assert.Equal(expectedRow, row);
+        Assert.Equal(expectedWidth, width);
+        Assert.Equal(expectedHeight, height);
+    }
+}

tests/ImageSharp.Tests/Formats/Heif/Hevc/HevcTransformUnitGeometryTests.cs

@@ -0,0 +1,74 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Heif.Hevc;
+
+namespace SixLabors.ImageSharp.Tests.Formats.Heif.Hevc;
+
+/// <summary>
+/// Verifies HEVC transform-tree component geometry across chroma sampling layouts.
+/// </summary>
+[Trait("Format", "Heic")]
+public class HevcTransformUnitGeometryTests
+{
+    /// <summary>
+    /// Verifies that a sub-minimum 4:2:0 chroma block is retained and processed with the final luma quadrant.
+    /// </summary>
+    [Fact]
+    public void Chroma420RetainsMinimumBlockAtFinalLumaQuadrant()
+    {
+        HevcTransformUnitGeometry root = HevcTransformUnitGeometry.CreateRoot(16, 24, 3, 1, false, 0);
+
+        for (int childIndex = 0; childIndex < 3; childIndex++)
+        {
+            HevcTransformUnitGeometry child = root.CreateChild(childIndex);
+            Assert.False(child.ChromaBlue.Process);
+        }
+
+        HevcTransformComponentGeometry chroma = root.CreateChild(3).ChromaBlue;
+        Assert.True(chroma.Process);
+        Assert.False(chroma.ProcessesAllQuadrants);
+        Assert.Equal(8, chroma.X);
+        Assert.Equal(12, chroma.Y);
+        Assert.Equal(4, chroma.Width);
+        Assert.Equal(4, chroma.Height);
+    }
+
+    /// <summary>
+    /// Verifies that a 4:2:2 rectangular chroma transform is retained for two vertical four-by-four coefficient blocks.
+    /// </summary>
+    [Fact]
+    public void Chroma422RetainsVerticalSubTransformsAtFinalLumaQuadrant()
+    {
+        HevcTransformUnitGeometry root = HevcTransformUnitGeometry.CreateRoot(16, 24, 3, 2, false, 0);
+
+        for (int childIndex = 0; childIndex < 3; childIndex++)
+        {
+            Assert.False(root.CreateChild(childIndex).ChromaBlue.Process);
+        }
+
+        HevcTransformComponentGeometry chroma = root.CreateChild(3).ChromaBlue;
+        Assert.True(chroma.Process);
+        Assert.False(chroma.ProcessesAllQuadrants);
+        Assert.Equal(8, chroma.X);
+        Assert.Equal(24, chroma.Y);
+        Assert.Equal(4, chroma.Width);
+        Assert.Equal(8, chroma.Height);
+    }
+
+    /// <summary>
+    /// Verifies that separate 4:4:4 planes retain full-resolution primary geometry and omit combined chroma syntax.
+    /// </summary>
+    [Fact]
+    public void SeparateColorPlaneUsesFullResolutionPrimaryGeometry()
+    {
+        HevcTransformUnitGeometry root = HevcTransformUnitGeometry.CreateRoot(16, 24, 5, 3, true, 2);
+
+        Assert.Equal(HevcPlane.Cr, root.PrimaryPlane);
+        Assert.Equal(16, root.Primary.X);
+        Assert.Equal(24, root.Primary.Y);
+        Assert.Equal(32, root.Primary.Width);
+        Assert.Equal(32, root.Primary.Height);
+        Assert.False(root.HasCombinedChroma);
+    }
+}