Implement AV1 lossless still-image coding

src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuColorConfig.cs

@@ -8,11 +8,6 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 /// </summary>
 internal sealed class ObuColorConfig
 {
-    /// <summary>
-    /// Stores whether the sequence uses a single monochrome plane.
-    /// </summary>
-    private bool isMonochrome;
-
     /// <summary>
     /// Gets or sets a value indicating whether color-description syntax is present.
     /// </summary>
@@ -21,23 +16,13 @@ internal sealed class ObuColorConfig
     /// <summary>
     /// Gets the number of color channels in this image. Can have the value 1 or 3.
     /// </summary>
-    public int PlaneCount { get; private set; }
+    public int PlaneCount => this.IsMonochrome ? 1 : Av1Constants.MaxPlanes;
 
     /// <summary>
     /// Gets or sets a value indicating whether the image has a single greyscale plane, will have
     /// <see cref="Av1Constants.MaxPlanes"/> color planes otherwise.
     /// </summary>
-    public bool IsMonochrome
-    {
-        get => this.isMonochrome;
-        set
-        {
-            // Plane count is derived from the monochrome flag throughout the decoder, so update
-            // both values atomically rather than allowing the two pieces of state to diverge.
-            this.PlaneCount = value ? 1 : Av1Constants.MaxPlanes;
-            this.isMonochrome = value;
-        }
-    }
+    public bool IsMonochrome { get; set; }
 
     /// <summary>
     /// Gets or sets the color-primary chromaticities.

src/ImageSharp/Formats/Heif/Av1/Pipeline/Av1EncoderModeDecisionWorkspace.cs

@@ -39,7 +39,8 @@ internal readonly ref struct Av1EncoderModeDecisionWorkspace<TSample>
     /// <summary>
     /// The maximum number of transform states needed while evaluating both chroma planes of one 128x128 block.
     /// </summary>
-    public const int MaximumCandidateTransformBlockCount = 32;
+    public const int MaximumCandidateTransformBlockCount =
+        2 * MaximumSampleCount / MinimumTransformSampleCount;
 
     /// <summary>
     /// The required workspace length in signed-integer storage elements.
@@ -48,6 +49,7 @@ internal readonly ref struct Av1EncoderModeDecisionWorkspace<TSample>
 
     private const int ReferenceBufferLength = (2 * Av1Constants.MaxTransformSize) + 1;
     private const int ReferenceBufferCount = 4;
+    private const int MinimumTransformSampleCount = 1 << (2 * Av1Constants.ModeInfoSizeLog2);
     private const int ReferenceStorageLength = ReferenceBufferCount * ReferenceBufferLength * sizeof(ushort) / sizeof(int);
     private const int CandidateSampleStorageOffset = ReferenceStorageLength;
     private const int CandidateSampleStorageLength = 2 * MaximumSampleCount * sizeof(ushort) / sizeof(int);

src/ImageSharp/Formats/Heif/Av1/Pipeline/Av1FrameEncoder.cs

@@ -119,7 +119,9 @@ internal static class Av1FrameEncoder
             ErrorResilientMode = true,
             RefreshFrameFlags = byte.MaxValue,
             DisableFrameEndUpdateCdf = true,
-            TransformMode = effort >= 6 ? Av1TransformMode.Select : Av1TransformMode.Largest,
+            TransformMode = qIndex == 0
+                ? Av1TransformMode.Only4x4
+                : effort >= 6 ? Av1TransformMode.Select : Av1TransformMode.Largest,
             ModeInfoColumnCount = modeInfoColumnCount,
             ModeInfoRowCount = modeInfoRowCount,
             TilesInfo = tiles,
@@ -294,14 +296,17 @@ internal static class Av1FrameEncoder
         }
 
         frameHeader.AllowScreenContentTools = allowScreenContentTools;
-        frameHeader.AllowIntraBlockCopy = allowIntraBlockCopy;
+
+        // The current IBC search is specialized for one 8x8 transform. Coded lossless requires reversible 4x4
+        // transforms, so retain palette search but omit this candidate until it has a matching tiled implementation.
+        frameHeader.AllowIntraBlockCopy = !frameHeader.CodedLossless && allowIntraBlockCopy;
         using Av1EncoderPictureBuffer picture = new(
             configuration,
             sequenceHeader,
             frameHeader,
             image.Width,
             image.Height,
-            disallow4x4AllFrames: effort < 9);
+            disallow4x4AllFrames: !frameHeader.CodedLossless && effort < 9);
 
         using Av1EncoderCoefficientBuffer coefficients = new(
             configuration,
@@ -358,14 +363,17 @@ internal static class Av1FrameEncoder
         }
 
         frameHeader.AllowScreenContentTools = allowScreenContentTools;
-        frameHeader.AllowIntraBlockCopy = allowIntraBlockCopy;
+
+        // The current IBC search is specialized for one 8x8 transform. Coded lossless requires reversible 4x4
+        // transforms, so retain palette search but omit this candidate until it has a matching tiled implementation.
+        frameHeader.AllowIntraBlockCopy = !frameHeader.CodedLossless && allowIntraBlockCopy;
         using Av1EncoderPictureBuffer picture = new(
             configuration,
             sequenceHeader,
             frameHeader,
             image.Width,
             image.Height,
-            disallow4x4AllFrames: effort < 9);
+            disallow4x4AllFrames: !frameHeader.CodedLossless && effort < 9);
 
         using Av1EncoderCoefficientBuffer coefficients = new(
             configuration,

src/ImageSharp/Formats/Heif/Av1/Pipeline/Av1IntraSuperblockEncoder.ChromaModeDecision.cs

@@ -805,10 +805,12 @@ internal static partial class Av1IntraSuperblockEncoder
             int transformHeight4x4 = transformSize.Get4x4HighCount();
             int maximumUnitWidth = Math.Min(maximumUnitBlockSize.GetWidth(), blockWidth);
             int maximumUnitHeight = Math.Min(maximumUnitBlockSize.GetHeight(), blockHeight);
-            Av1TransformType transformType = Av1SymbolContextHelper.GetDefaultIntraTransformType(
-                predictionMode,
-                transformSize,
-                this.picture.Parent.FrameHeader.UseReducedTransformSet);
+            Av1TransformType transformType = this.picture.Parent.FrameHeader.CodedLossless
+                ? Av1TransformType.DctDct
+                : Av1SymbolContextHelper.GetDefaultIntraTransformType(
+                    predictionMode,
+                    transformSize,
+                    this.picture.Parent.FrameHeader.UseReducedTransformSet);
 
             Av1ComponentType componentType = plane == Av1Plane.Y
                 ? Av1ComponentType.Luminance
@@ -1046,10 +1048,12 @@ internal static partial class Av1IntraSuperblockEncoder
 
             // Intra chroma derives one transform type from the shared UV prediction mode. The type is not
             // signaled independently for either chroma plane, so U and V must use the same legal fallback.
-            Av1TransformType transformType = Av1SymbolContextHelper.GetDefaultIntraTransformType(
-                predictionMode,
-                transformSize,
-                this.picture.Parent.FrameHeader.UseReducedTransformSet);
+            Av1TransformType transformType = this.picture.Parent.FrameHeader.CodedLossless
+                ? Av1TransformType.DctDct
+                : Av1SymbolContextHelper.GetDefaultIntraTransformType(
+                    predictionMode,
+                    transformSize,
+                    this.picture.Parent.FrameHeader.UseReducedTransformSet);
 
             long distortion = TOperator.EncodeCandidate(
                 this.blockWorkspace,

src/ImageSharp/Formats/Heif/Av1/Pipeline/Av1IntraSuperblockEncoder.ModeDecision.cs

@@ -544,7 +544,10 @@ internal static partial class Av1IntraSuperblockEncoder
         {
             Av1BlockSize blockSize = modeInfo.Block.BlockSize;
             Av1PartitionType partitionType = modeInfo.Block.PartitionType;
-            Av1TransformSize maximumLumaTransformSize = blockSize.GetMaximumTransformSize();
+            Av1TransformSize maximumLumaTransformSize = this.picture.Parent.FrameHeader.CodedLossless
+                ? Av1TransformSize.Size4x4
+                : blockSize.GetMaximumTransformSize();
+
             int qIndex = this.quantization.QIndex[0];
             modeInfo.Block = new Av1EncoderBlockModeInfo
             {
@@ -619,8 +622,9 @@ internal static partial class Av1IntraSuperblockEncoder
                         block.FilterIntraMode)
                     : 0;
 
-                modeInfo.Block.Skip = lumaTransformEmpty &&
-                    Av1TileWriter.ShouldSkipCoefficients(
+                modeInfo.Block.Skip =
+                    !this.picture.Parent.FrameHeader.CodedLossless &&
+                    lumaTransformEmpty && Av1TileWriter.ShouldSkipCoefficients(
                         writer,
                         Av1TileWriter.GetSkipContext(macroBlock),
                         emptyTransformRate);
@@ -660,9 +664,11 @@ internal static partial class Av1IntraSuperblockEncoder
                 subsamplingX,
                 subsamplingY);
 
-            Av1TransformSize chromaTransformSize = blockSize.GetMaxUvTransformSize(
-                colorConfig.SubSamplingX,
-                colorConfig.SubSamplingY);
+            Av1TransformSize chromaTransformSize = this.picture.Parent.FrameHeader.CodedLossless
+                ? Av1TransformSize.Size4x4
+                : blockSize.GetMaxUvTransformSize(
+                    colorConfig.SubSamplingX,
+                    colorConfig.SubSamplingY);
 
             Av1BlockSize chromaBlockSize = blockSize.GetSubsampled(
                 colorConfig.SubSamplingX,
@@ -763,7 +769,8 @@ internal static partial class Av1IntraSuperblockEncoder
                         Av1FilterIntraMode.AllFilterIntraModes);
                 }
 
-                modeInfo.Block.Skip = Av1TileWriter.ShouldSkipCoefficients(
+                modeInfo.Block.Skip = !this.picture.Parent.FrameHeader.CodedLossless &&
+                    Av1TileWriter.ShouldSkipCoefficients(
                     writer,
                     Av1TileWriter.GetSkipContext(macroBlock),
                     regularEmptyTransformRate);
@@ -1336,7 +1343,11 @@ internal static partial class Av1IntraSuperblockEncoder
             out Av1TransformSize selectedTransformSize,
             out long selectedCost)
         {
-            Av1TransformSize transformSize = blockSize.GetMaximumTransformSize();
+            bool codedLossless = this.picture.Parent.FrameHeader.CodedLossless;
+            Av1TransformSize transformSize = codedLossless
+                ? Av1TransformSize.Size4x4
+                : blockSize.GetMaximumTransformSize();
+
             int blockWidth = blockSize.GetWidth();
             int blockHeight = blockSize.GetHeight();
             Av1EncoderModeDecisionWorkspace<TSample> workspace =
@@ -1530,8 +1541,9 @@ internal static partial class Av1IntraSuperblockEncoder
 
             // Transform type and transform size are separate search axes. Splitting their effort thresholds
             // gives callers a useful intermediate tier without changing the fast default path.
-            bool searchEveryTransformType = this.effort >= 7;
-            bool searchEveryTransformSize = this.effort >= 8 &&
+            bool searchEveryTransformType = !codedLossless && this.effort >= 7;
+            bool searchEveryTransformSize = !codedLossless &&
+                this.effort >= 8 &&
                 transformSize == Av1TransformSize.Size8x8;
 
             // Zero-angle modes precede groups of six nonzero adjustments for each directional mode.
@@ -1571,12 +1583,14 @@ internal static partial class Av1IntraSuperblockEncoder
 
                 // Transform types are visited in AV1 enumeration order. A strict cost comparison below keeps
                 // the first legal type on ties, while lower efforts visit only the mode-derived default.
-                Av1TransformType firstTransformType = searchEveryTransformType
+                Av1TransformType firstTransformType = codedLossless
                     ? Av1TransformType.DctDct
-                    : Av1SymbolContextHelper.GetDefaultIntraTransformType(
-                        mode,
-                        transformSize,
-                        useReducedTransformSet);
+                    : searchEveryTransformType
+                        ? Av1TransformType.DctDct
+                        : Av1SymbolContextHelper.GetDefaultIntraTransformType(
+                            mode,
+                            transformSize,
+                            useReducedTransformSet);
 
                 Av1TransformType transformTypeLimit = searchEveryTransformType
                     ? Av1TransformType.AllTransformTypes
@@ -1679,7 +1693,7 @@ internal static partial class Av1IntraSuperblockEncoder
             // Midrange effort refines the preliminary mode only. Higher effort already searched every
             // mode-transform pair above, so repeating the winning mode would add no candidates.
             long bestTransformCost = bestCost;
-            if (this.effort >= 3 && !searchEveryTransformType)
+            if (!codedLossless && this.effort >= 3 && !searchEveryTransformType)
             {
                 // The shared spans now contain the last mode visited above, so rebuild the preliminary
                 // winner once before refining its transform types.
@@ -1767,8 +1781,12 @@ internal static partial class Av1IntraSuperblockEncoder
                         transformSize,
                         this.bitDepth);
 
+                    Av1TransformType filterTransformTypeLimit = codedLossless
+                        ? (Av1TransformType)((int)Av1TransformType.DctDct + 1)
+                        : Av1TransformType.AllTransformTypes;
+
                     for (Av1TransformType transformType = Av1TransformType.DctDct;
-                        transformType < Av1TransformType.AllTransformTypes;
+                        transformType < filterTransformTypeLimit;
                         transformType++)
                     {
                         if (!transformType.IsExtendedSetUsed(transformSetType))

src/ImageSharp/Formats/Heif/Av1/Pipeline/Av1TransformBlockEncoder.cs

@@ -223,10 +223,10 @@ internal static class Av1TransformBlockEncoder
                 reconstruction,
                 reconstructionStride,
                 transformSize,
-                transformType,
+                state.TransformType,
                 (int)plane,
                 state.EndOfBlock,
-                false,
+                qIndex == 0,
                 workspace.TransformWorkspace);
         }
 
@@ -310,10 +310,10 @@ internal static class Av1TransformBlockEncoder
                 reconstruction,
                 width,
                 transformSize,
-                Av1TransformType.DctDct,
+                state.TransformType,
                 (int)plane,
                 state.EndOfBlock,
-                false,
+                qIndex == 0,
                 workspace.TransformWorkspace);
         }
 
@@ -549,10 +549,10 @@ internal static class Av1TransformBlockEncoder
                 MemoryMarshal.Cast<ushort, short>(reconstruction),
                 reconstructionStride,
                 transformSize,
-                transformType,
+                state.TransformType,
                 (int)plane,
                 state.EndOfBlock,
-                false,
+                qIndex == 0,
                 bitDepth,
                 workspace.TransformWorkspace);
         }
@@ -652,10 +652,10 @@ internal static class Av1TransformBlockEncoder
                 signedReconstruction,
                 width,
                 transformSize,
-                Av1TransformType.DctDct,
+                state.TransformType,
                 (int)plane,
                 state.EndOfBlock,
-                false,
+                qIndex == 0,
                 bitDepth,
                 workspace.TransformWorkspace);
         }
@@ -913,10 +913,10 @@ internal static class Av1TransformBlockEncoder
                 reconstruction,
                 reconstructionStride,
                 transformSize,
-                transformType,
+                state.TransformType,
                 (int)plane,
                 state.EndOfBlock,
-                false,
+                qIndex == 0,
                 workspace.TransformWorkspace);
         }
     }
@@ -1001,10 +1001,10 @@ internal static class Av1TransformBlockEncoder
                 MemoryMarshal.Cast<ushort, short>(reconstruction),
                 reconstructionStride,
                 transformSize,
-                transformType,
+                state.TransformType,
                 (int)plane,
                 state.EndOfBlock,
-                false,
+                qIndex == 0,
                 bitDepth,
                 workspace.TransformWorkspace);
         }
@@ -1061,6 +1061,16 @@ internal static class Av1TransformBlockEncoder
         Span<int> quantized = quantizedCoefficients[..coefficientCount];
         Span<int> dequantized = workspace.DequantizedCoefficients[..coefficientCount];
 
+        if (qIndex == 0)
+        {
+            // A coded-lossless frame fixes every transform block at 4x4 and uses the reversible transform. Its
+            // quantizer removes only the transform's fixed scale, leaving reconstruction coefficients unchanged.
+            Av1ForwardTransformer.TransformLossless4x4(residual, transformed, (uint)transformSize.GetWidth());
+            state.EndOfBlock = Av1ForwardQuantizer.QuantizeLossless(transformed, quantized, dequantized, bitDepth);
+            state.TransformType = Av1TransformType.DctDct;
+            return;
+        }
+
         // The forward transform reads the prepared residual without changing it, so every type candidate can
         // reuse one source-minus-prediction block. Separate coefficient spans preserve each later representation.
         Av1ForwardTransformer.Transform2d(

src/ImageSharp/Formats/Heif/Av1/Pipeline/Quantizers/Av1ForwardQuantizer.Operator.cs

@@ -202,4 +202,174 @@ internal static partial class Av1ForwardQuantizer
             return quantized;
         }
     }
+
+    /// <summary>
+    /// Implements fast no-matrix quantization without truncating high-bit-depth transform magnitudes.
+    /// </summary>
+    /// <remarks>
+    /// The reciprocal product is widened to 64 bits because 10-bit and 12-bit transforms can exceed the signed
+    /// 16-bit range. Each SIMD overload preserves the scalar fixed-point operation order in every lane.
+    /// </remarks>
+    internal readonly struct HighBitDepthFastQuantizationOperator : IForwardQuantizationOperator
+    {
+        /// <inheritdoc/>
+        public static Vector128<int> Quantize(
+            Vector128<int> coefficients,
+            Vector128<int> rounding,
+            Vector128<int> quantizer,
+            Vector128<int> dequantizer,
+            int logScale,
+            out Vector128<int> dequantizedCoefficients)
+        {
+            Vector128<int> coefficientSign = Vector128.ShiftRightArithmetic(coefficients, 31);
+            Vector128<int> magnitude = Vector128.Abs(coefficients);
+            Vector128<int> thresholdMask = ~Vector128.GreaterThan(dequantizer, magnitude << (1 + logScale));
+            Vector128<int> rounded = magnitude + rounding;
+
+            // Widen before multiplying so transform magnitudes above 32,767 retain their full precision.
+            Vector128<long> lowerProduct = Vector128.WidenLower(rounded) * Vector128.WidenLower(quantizer);
+            Vector128<long> upperProduct = Vector128.WidenUpper(rounded) * Vector128.WidenUpper(quantizer);
+            Vector128<int> quantizedMagnitude =
+                Vector128.Narrow(lowerProduct >> (16 - logScale), upperProduct >> (16 - logScale)) & thresholdMask;
+
+            Vector128<int> quantized = (quantizedMagnitude ^ coefficientSign) - coefficientSign;
+            Vector128<int> dequantizedMagnitude = (quantizedMagnitude * dequantizer) >> logScale;
+            dequantizedCoefficients = (dequantizedMagnitude ^ coefficientSign) - coefficientSign;
+            return quantized;
+        }
+
+        /// <inheritdoc/>
+        public static Vector256<int> Quantize(
+            Vector256<int> coefficients,
+            Vector256<int> rounding,
+            Vector256<int> quantizer,
+            Vector256<int> dequantizer,
+            int logScale,
+            out Vector256<int> dequantizedCoefficients)
+        {
+            Vector256<int> coefficientSign = Vector256.ShiftRightArithmetic(coefficients, 31);
+            Vector256<int> magnitude = Vector256.Abs(coefficients);
+            Vector256<int> thresholdMask = ~Vector256.GreaterThan(dequantizer, magnitude << (1 + logScale));
+            Vector256<int> rounded = magnitude + rounding;
+
+            // Widen before multiplying so transform magnitudes above 32,767 retain their full precision.
+            Vector256<long> lowerProduct = Vector256.WidenLower(rounded) * Vector256.WidenLower(quantizer);
+            Vector256<long> upperProduct = Vector256.WidenUpper(rounded) * Vector256.WidenUpper(quantizer);
+            Vector256<int> quantizedMagnitude =
+                Vector256.Narrow(lowerProduct >> (16 - logScale), upperProduct >> (16 - logScale)) & thresholdMask;
+
+            Vector256<int> quantized = (quantizedMagnitude ^ coefficientSign) - coefficientSign;
+            Vector256<int> dequantizedMagnitude = (quantizedMagnitude * dequantizer) >> logScale;
+            dequantizedCoefficients = (dequantizedMagnitude ^ coefficientSign) - coefficientSign;
+            return quantized;
+        }
+
+        /// <inheritdoc/>
+        public static Vector512<int> Quantize(
+            Vector512<int> coefficients,
+            Vector512<int> rounding,
+            Vector512<int> quantizer,
+            Vector512<int> dequantizer,
+            int logScale,
+            out Vector512<int> dequantizedCoefficients)
+        {
+            Vector512<int> coefficientSign = Vector512.ShiftRightArithmetic(coefficients, 31);
+            Vector512<int> magnitude = Vector512.Abs(coefficients);
+            Vector512<int> thresholdMask = ~Vector512.GreaterThan(dequantizer, magnitude << (1 + logScale));
+            Vector512<int> rounded = magnitude + rounding;
+
+            // Widen before multiplying so transform magnitudes above 32,767 retain their full precision.
+            Vector512<long> lowerProduct = Vector512.WidenLower(rounded) * Vector512.WidenLower(quantizer);
+            Vector512<long> upperProduct = Vector512.WidenUpper(rounded) * Vector512.WidenUpper(quantizer);
+            Vector512<int> quantizedMagnitude =
+                Vector512.Narrow(lowerProduct >> (16 - logScale), upperProduct >> (16 - logScale)) & thresholdMask;
+
+            Vector512<int> quantized = (quantizedMagnitude ^ coefficientSign) - coefficientSign;
+            Vector512<int> dequantizedMagnitude = (quantizedMagnitude * dequantizer) >> logScale;
+            dequantizedCoefficients = (dequantizedMagnitude ^ coefficientSign) - coefficientSign;
+            return quantized;
+        }
+
+        /// <inheritdoc/>
+        public static int Quantize(
+            int coefficient,
+            int rounding,
+            int quantizer,
+            int dequantizer,
+            int logScale,
+            out int dequantizedCoefficient)
+        {
+            int coefficientSign = coefficient >> 31;
+            int magnitude = (coefficient ^ coefficientSign) - coefficientSign;
+            int quantizedMagnitude = 0;
+
+            if (((long)magnitude << (1 + logScale)) >= dequantizer)
+            {
+                quantizedMagnitude = (int)((((long)magnitude + rounding) * quantizer) >> (16 - logScale));
+            }
+
+            int quantized = (quantizedMagnitude ^ coefficientSign) - coefficientSign;
+            int dequantizedMagnitude = (quantizedMagnitude * dequantizer) >> logScale;
+            dequantizedCoefficient = (dequantizedMagnitude ^ coefficientSign) - coefficientSign;
+            return quantized;
+        }
+    }
+
+    /// <summary>
+    /// Removes the reversible transform's fixed scale for entropy coding while retaining exact reconstruction coefficients.
+    /// </summary>
+    internal readonly struct LosslessQuantizationOperator : IForwardQuantizationOperator
+    {
+        /// <inheritdoc/>
+        public static Vector128<int> Quantize(
+            Vector128<int> coefficients,
+            Vector128<int> rounding,
+            Vector128<int> quantizer,
+            Vector128<int> dequantizer,
+            int logScale,
+            out Vector128<int> dequantizedCoefficients)
+        {
+            dequantizedCoefficients = coefficients;
+            return coefficients >> 2;
+        }
+
+        /// <inheritdoc/>
+        public static Vector256<int> Quantize(
+            Vector256<int> coefficients,
+            Vector256<int> rounding,
+            Vector256<int> quantizer,
+            Vector256<int> dequantizer,
+            int logScale,
+            out Vector256<int> dequantizedCoefficients)
+        {
+            dequantizedCoefficients = coefficients;
+            return coefficients >> 2;
+        }
+
+        /// <inheritdoc/>
+        public static Vector512<int> Quantize(
+            Vector512<int> coefficients,
+            Vector512<int> rounding,
+            Vector512<int> quantizer,
+            Vector512<int> dequantizer,
+            int logScale,
+            out Vector512<int> dequantizedCoefficients)
+        {
+            dequantizedCoefficients = coefficients;
+            return coefficients >> 2;
+        }
+
+        /// <inheritdoc/>
+        public static int Quantize(
+            int coefficient,
+            int rounding,
+            int quantizer,
+            int dequantizer,
+            int logScale,
+            out int dequantizedCoefficient)
+        {
+            dequantizedCoefficient = coefficient;
+            return coefficient >> 2;
+        }
+    }
 }

src/ImageSharp/Formats/Heif/Av1/Pipeline/Quantizers/Av1ForwardQuantizer.cs

@@ -36,21 +36,56 @@ internal static partial class Av1ForwardQuantizer
         int dcDeltaQ,
         int acDeltaQ,
         Av1BitDepth bitDepth)
-        => QuantizeLossy<FastQuantizationOperator>(
+        => bitDepth == Av1BitDepth.EightBit
+            ? Quantize<FastQuantizationOperator>(
+                coefficients,
+                quantizedCoefficients,
+                dequantizedCoefficients,
+                transformSize,
+                transformType,
+                qIndex,
+                dcDeltaQ,
+                acDeltaQ,
+                bitDepth)
+            : Quantize<HighBitDepthFastQuantizationOperator>(
+                coefficients,
+                quantizedCoefficients,
+                dequantizedCoefficients,
+                transformSize,
+                transformType,
+                qIndex,
+                dcDeltaQ,
+                acDeltaQ,
+                bitDepth);
+
+    /// <summary>
+    /// Quantizes one reversible four-by-four transform without changing its reconstruction coefficients.
+    /// </summary>
+    /// <param name="coefficients">The raster-order reversible-transform coefficients.</param>
+    /// <param name="quantizedCoefficients">The raster-order entropy-coding coefficients.</param>
+    /// <param name="dequantizedCoefficients">The raster-order reconstruction coefficients.</param>
+    /// <param name="bitDepth">The coded sample bit depth.</param>
+    /// <returns>The one-based end position in coefficient scan order.</returns>
+    public static ushort QuantizeLossless(
+        ReadOnlySpan<int> coefficients,
+        Span<int> quantizedCoefficients,
+        Span<int> dequantizedCoefficients,
+        Av1BitDepth bitDepth)
+        => Quantize<LosslessQuantizationOperator>(
             coefficients,
             quantizedCoefficients,
             dequantizedCoefficients,
-            transformSize,
-            transformType,
-            qIndex,
-            dcDeltaQ,
-            acDeltaQ,
+            Av1TransformSize.Size4x4,
+            Av1TransformType.DctDct,
+            0,
+            0,
+            0,
             bitDepth);
 
     /// <summary>
     /// Applies a closed generic quantization operator across the widest available hardware widths.
     /// </summary>
-    internal static ushort QuantizeLossy<TOperator>(
+    private static ushort Quantize<TOperator>(
         ReadOnlySpan<int> coefficients,
         Span<int> quantizedCoefficients,
         Span<int> dequantizedCoefficients,

src/ImageSharp/Formats/Heif/Av1/Transform/Av1ForwardTransformer.cs

@@ -45,6 +45,133 @@ internal static partial class Av1ForwardTransformer
         DispatchColumn(input, coefficients, stride, bitDepth, ref config, workspace);
     }
 
+    /// <summary>
+    /// Applies the reversible four-by-four transform required by coded-lossless AV1 blocks.
+    /// </summary>
+    /// <param name="input">The spatial residual samples.</param>
+    /// <param name="coefficients">The destination transform coefficients.</param>
+    /// <param name="stride">The number of input samples between rows.</param>
+    public static void TransformLossless4x4(ReadOnlySpan<short> input, Span<int> coefficients, uint stride)
+    {
+        int inputStride = (int)stride;
+
+        if (Vector128.IsHardwareAccelerated)
+        {
+            Vector128<int> row0 = Vector128.Create((int)input[0], input[1], input[2], input[3]);
+            Vector128<int> row1 = Vector128.Create(
+                input[inputStride],
+                input[inputStride + 1],
+                input[inputStride + 2],
+                input[inputStride + 3]);
+
+            Vector128<int> row2 = Vector128.Create(
+                input[2 * inputStride],
+                input[(2 * inputStride) + 1],
+                input[(2 * inputStride) + 2],
+                input[(2 * inputStride) + 3]);
+
+            Vector128<int> row3 = Vector128.Create(
+                input[3 * inputStride],
+                input[(3 * inputStride) + 1],
+                input[(3 * inputStride) + 2],
+                input[(3 * inputStride) + 3]);
+
+            // Each lane initially holds one column. The first stage transforms those columns in parallel, then the
+            // transpose makes each transformed column a row so the same lane-wise network can process the other axis.
+            TransformLosslessStage(ref row0, ref row1, ref row2, ref row3);
+            Av1Transform2dOperations.Transpose(ref row0, ref row1, ref row2, ref row3);
+            TransformLosslessStage(ref row0, ref row1, ref row2, ref row3);
+
+            // The entropy pipeline stores transform positions in row-major order, while the reversible reference
+            // walk leaves the two frequency axes exchanged. Normalize that boundary before scan-order traversal.
+            Av1Transform2dOperations.Transpose(ref row0, ref row1, ref row2, ref row3);
+
+            ref int coefficientBase = ref MemoryMarshal.GetReference(coefficients);
+            (row0 * 4).StoreUnsafe(ref coefficientBase);
+            (row1 * 4).StoreUnsafe(ref coefficientBase, 4);
+            (row2 * 4).StoreUnsafe(ref coefficientBase, 8);
+            (row3 * 4).StoreUnsafe(ref coefficientBase, 12);
+            return;
+        }
+
+        // The first pass writes transposed columns into the destination, matching the layout consumed in-place by
+        // the second pass. This keeps the scalar fallback allocation-free without a temporary matrix.
+        for (int column = 0; column < 4; column++)
+        {
+            int a = input[column];
+            int b = input[inputStride + column];
+            int c = input[(2 * inputStride) + column];
+            int d = input[(3 * inputStride) + column];
+
+            a += b;
+            d -= c;
+            int e = (a - d) >> 1;
+            b = e - b;
+            c = e - c;
+            a -= c;
+            d += b;
+
+            int offset = column * 4;
+            coefficients[offset] = a;
+            coefficients[offset + 1] = c;
+            coefficients[offset + 2] = d;
+            coefficients[offset + 3] = b;
+        }
+
+        for (int column = 0; column < 4; column++)
+        {
+            int a = coefficients[column];
+            int b = coefficients[4 + column];
+            int c = coefficients[8 + column];
+            int d = coefficients[12 + column];
+
+            a += b;
+            d -= c;
+            int e = (a - d) >> 1;
+            b = e - b;
+            c = e - c;
+            a -= c;
+            d += b;
+
+            coefficients[column] = a * 4;
+            coefficients[4 + column] = c * 4;
+            coefficients[8 + column] = d * 4;
+            coefficients[12 + column] = b * 4;
+        }
+
+        // Normalize the scalar reference walk to the row-major coefficient contract used by entropy coding.
+        (coefficients[1], coefficients[4]) = (coefficients[4], coefficients[1]);
+        (coefficients[2], coefficients[8]) = (coefficients[8], coefficients[2]);
+        (coefficients[3], coefficients[12]) = (coefficients[12], coefficients[3]);
+        (coefficients[6], coefficients[9]) = (coefficients[9], coefficients[6]);
+        (coefficients[7], coefficients[13]) = (coefficients[13], coefficients[7]);
+        (coefficients[11], coefficients[14]) = (coefficients[14], coefficients[11]);
+    }
+
+    /// <summary>
+    /// Applies one axis of the reversible four-point transform to four independent SIMD lanes.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static void TransformLosslessStage(
+        ref Vector128<int> row0,
+        ref Vector128<int> row1,
+        ref Vector128<int> row2,
+        ref Vector128<int> row3)
+    {
+        Vector128<int> a = row0 + row1;
+        Vector128<int> d = row3 - row2;
+        Vector128<int> e = (a - d) >> 1;
+        Vector128<int> b = e - row1;
+        Vector128<int> c = e - row2;
+        a -= c;
+        d += b;
+
+        row0 = a;
+        row1 = c;
+        row2 = d;
+        row3 = b;
+    }
+
     /// <summary>
     /// Selects the concrete column operator for a transform block.
     /// </summary>

src/ImageSharp/Formats/Heif/HeifEncoderCore.cs

@@ -786,11 +786,6 @@ internal sealed class HeifEncoderCore
         CancellationToken cancellationToken)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        if (this.encoder.Lossless)
-        {
-            throw new NotSupportedException("Lossless AV1 encoding is not implemented.");
-        }
-
         if (image.Frames.Count != 1)
         {
             throw new NotSupportedException("AV1 image-sequence encoding is not implemented.");
@@ -806,8 +801,12 @@ internal sealed class HeifEncoderCore
             _ => throw new NotSupportedException($"HEIF bit depth '{bitDepth}' is not supported.")
         };
 
+        HeifChromaSubsampling defaultChromaSubsampling = this.encoder.Lossless
+            ? HeifChromaSubsampling.Yuv444
+            : HeifChromaSubsampling.Yuv420;
+
         HeifChromaSubsampling chromaSubsampling = this.encoder.ChromaSubsampling ??
-            (metadata.IsMonochrome ? HeifChromaSubsampling.Monochrome : HeifChromaSubsampling.Yuv420);
+            (metadata.IsMonochrome ? HeifChromaSubsampling.Monochrome : defaultChromaSubsampling);
 
         (bool isMonochrome, bool subsamplingX, bool subsamplingY) = chromaSubsampling switch
         {
@@ -871,7 +870,7 @@ internal sealed class HeifEncoderCore
         };
 
         int quality = this.encoder.Quality ?? 75;
-        int qIndex = GetAv1QuantizerIndex(quality);
+        int qIndex = this.encoder.Lossless ? 0 : GetAv1QuantizerIndex(quality);
         cancellationToken.ThrowIfCancellationRequested();
         ObuSequenceHeader colorHeader = Av1FrameEncoder.Encode(
             this.configuration,
@@ -910,7 +909,7 @@ internal sealed class HeifEncoderCore
             };
 
             int alphaQuality = this.encoder.AlphaQuality ?? quality;
-            int alphaQIndex = GetAv1QuantizerIndex(alphaQuality);
+            int alphaQIndex = this.encoder.Lossless ? 0 : GetAv1QuantizerIndex(alphaQuality);
             cancellationToken.ThrowIfCancellationRequested();
             long alphaOffset = stream.Length;
             ObuSequenceHeader alphaHeader = Av1FrameEncoder.EncodeAlpha(

tests/ImageSharp.Tests/Formats/Heif/Av1/Av1EncoderFrameTests.cs

@@ -153,6 +153,95 @@ public class Av1EncoderFrameTests
         }
     }
 
+    [Theory]
+    [InlineData(TenBit)]
+    [InlineData(TwelveBit)]
+    public void LosslessHighBitDepthEncodingPreservesNativePlanes(int bitDepthValue)
+    {
+        const int width = 8;
+        const int height = 8;
+        Av1BitDepth bitDepth = (Av1BitDepth)bitDepthValue;
+        using Image<Rgb48> source = new(width, height);
+        for (int row = 0; row < height; row++)
+        {
+            Span<Rgb48> pixels = source.Frames.RootFrame.PixelBuffer.DangerousGetRowSpan(row);
+            for (int column = 0; column < width; column++)
+            {
+                pixels[column] = new Rgb48(
+                    (ushort)((column * 7001) + (row * 997)),
+                    (ushort)((row * 6007) + (column * 1231)),
+                    (ushort)((column * 4001) + (row * 3001)));
+            }
+        }
+
+        ObuColorConfig colorConfig = new()
+        {
+            IsColorDescriptionPresent = true,
+            ColorPrimaries = ObuColorPrimaries.Bt709,
+            TransferCharacteristics = ObuTransferCharacteristics.Srgb,
+            MatrixCoefficients = ObuMatrixCoefficients.Identity,
+            ColorRange = true,
+            BitDepth = bitDepth
+        };
+
+        using Av1EncoderFrameBuffer<ushort> expected = new(
+            Configuration.Default,
+            width,
+            height,
+            bitDepth.GetBitCount(),
+            Av1ColorFormat.Yuv444,
+            1,
+            1);
+
+        Av1FrameEncoder.PrepareSource(
+            Configuration.Default,
+            source.Frames.RootFrame,
+            expected.Frame,
+            colorConfig);
+
+        using MemoryStream stream = new();
+        Av1FrameEncoder.Encode(
+            Configuration.Default,
+            source.Frames.RootFrame,
+            stream,
+            colorConfig,
+            qIndex: 0,
+            effort: 0);
+
+        byte[] payload = stream.ToArray();
+        string outputDirectory = Path.Combine(
+            TestEnvironment.ActualOutputDirectoryFullPath,
+            "Formats",
+            "Heif",
+            "Av1");
+
+        Directory.CreateDirectory(outputDirectory);
+        File.WriteAllBytes(
+            Path.Combine(outputDirectory, $"encoder-frame-8x8-{bitDepth.GetBitCount()}b-444-lossless.obu"),
+            payload);
+
+        using Av1Decoder decoder = new(Configuration.Default);
+        using Av1FrameBuffer<byte> actual = decoder.DecodeFrameBuffer(payload, null, null, out _);
+        ObuFrameHeader frameHeader = Assert.IsType<ObuFrameHeader>(decoder.FrameHeader);
+
+        Assert.Equal(width, actual.Width);
+        Assert.Equal(height, actual.Height);
+        Assert.True(frameHeader.CodedLossless);
+        Assert.True(frameHeader.AllLossless);
+        Assert.Equal(Av1TransformMode.Only4x4, frameHeader.TransformMode);
+
+        foreach (Av1Plane plane in new[] { Av1Plane.Y, Av1Plane.U, Av1Plane.V })
+        {
+            Buffer2DRegion<ushort> expectedPlane = expected.Frame.View.GetPlane(plane);
+            for (int row = 0; row < height; row++)
+            {
+                Assert.Equal(
+                    expectedPlane.DangerousGetRowSpan(row)[..width].ToArray(),
+                    actual.GetHighBitDepthRowSpan(plane, row, 0, 0).ToArray());
+            }
+        }
+    }
+
     [Fact]
     public void EncodeEffortNineSelectsSubEightPartition()
     {

tests/ImageSharp.Tests/Formats/Heif/Av1/Av1ForwardQuantizerTests.cs

@@ -68,6 +68,34 @@ public class Av1ForwardQuantizerTests
         Assert.Equal(0, GC.GetAllocatedBytesForCurrentThread() - before);
     }
 
+    /// <summary>
+    /// Verifies that lossless quantization removes only the reversible transform scale.
+    /// </summary>
+    [Fact]
+    public void LosslessQuantizerRetainsExactReconstructionCoefficients()
+    {
+        int[] coefficients =
+        [
+            4, -8, 12, -16,
+            20, -24, 28, -32,
+            36, -40, 44, -48,
+            52, -56, 60, -64
+        ];
+
+        int[] quantized = new int[coefficients.Length];
+        int[] dequantized = new int[coefficients.Length];
+
+        ushort endOfBlock = Av1ForwardQuantizer.QuantizeLossless(
+            coefficients,
+            quantized,
+            dequantized,
+            Av1BitDepth.TwelveBit);
+
+        Assert.Equal((ushort)16, endOfBlock);
+        Assert.Equal(coefficients.Select(x => x / 4), quantized);
+        Assert.Equal(coefficients, dequantized);
+    }
+
     /// <summary>
     /// Exercises each transform-scale category, coded 64-point layout, quantizer range, and sample precision.
     /// </summary>
@@ -188,7 +216,12 @@ public class Av1ForwardQuantizerTests
 
             if ((magnitude << (1 + logScale)) >= dequantizer)
             {
-                magnitude = Math.Clamp(magnitude + rounding, short.MinValue, short.MaxValue);
+                magnitude += rounding;
+                if (bitDepth == Av1BitDepth.EightBit)
+                {
+                    magnitude = Math.Min(magnitude, short.MaxValue);
+                }
+
                 quantizedMagnitude = (int)((magnitude * quantizer) >> (16 - logScale));
             }
 

tests/ImageSharp.Tests/Formats/Heif/Av1/Av1ForwardTransformTests.cs

@@ -61,6 +61,13 @@ public class Av1ForwardTransformTests
     public void TwoDimensionalPipelineMatchesReference()
         => FeatureTestRunner.RunWithHwIntrinsicsFeature(AssertTwoDimensionalPipeline, TransformConfigurations);
 
+    /// <summary>
+    /// Verifies the reversible transform against the independent scalar operation order at every hardware tier.
+    /// </summary>
+    [Fact]
+    public void LosslessTransformMatchesLibaomReferenceAcrossHardwareWidths()
+        => FeatureTestRunner.RunWithHwIntrinsicsFeature(AssertLosslessTransform, TransformConfigurations);
+
     /// <summary>
     /// Verifies that the complete transform dispatcher reuses caller-owned workspace.
     /// </summary>
@@ -83,6 +90,90 @@ public class Av1ForwardTransformTests
         Assert.Equal(0, GC.GetAllocatedBytesForCurrentThread() - before);
     }
 
+    private static void AssertLosslessTransform()
+    {
+        const int stride = 7;
+        short[] input = new short[stride * 4];
+        for (int row = 0; row < 4; row++)
+        {
+            for (int column = 0; column < 4; column++)
+            {
+                input[(row * stride) + column] = (short)((row * 1003) - (column * 499) + (row * column * 71) - 1024);
+            }
+        }
+
+        int[] expected = new int[16];
+        int[] actual = new int[16];
+        TransformLosslessReference(input, expected, stride);
+        Av1ForwardTransformer.TransformLossless4x4(input, actual, stride);
+
+        Assert.Equal(expected, actual);
+
+        long before = GC.GetAllocatedBytesForCurrentThread();
+        for (int iteration = 0; iteration < 32; iteration++)
+        {
+            Av1ForwardTransformer.TransformLossless4x4(input, actual, stride);
+        }
+
+        Assert.Equal(0, GC.GetAllocatedBytesForCurrentThread() - before);
+    }
+
+    private static void TransformLosslessReference(ReadOnlySpan<short> input, Span<int> output, int stride)
+    {
+        // The first pass traverses columns and writes their four transformed values contiguously. The second
+        // pass consumes that transposed layout in place, matching the normative reversible operation order.
+        for (int column = 0; column < 4; column++)
+        {
+            int a = input[column];
+            int b = input[stride + column];
+            int c = input[(2 * stride) + column];
+            int d = input[(3 * stride) + column];
+
+            a += b;
+            d -= c;
+            int e = (a - d) >> 1;
+            b = e - b;
+            c = e - c;
+            a -= c;
+            d += b;
+
+            int offset = column * 4;
+            output[offset] = a;
+            output[offset + 1] = c;
+            output[offset + 2] = d;
+            output[offset + 3] = b;
+        }
+
+        for (int column = 0; column < 4; column++)
+        {
+            int a = output[column];
+            int b = output[4 + column];
+            int c = output[8 + column];
+            int d = output[12 + column];
+
+            a += b;
+            d -= c;
+            int e = (a - d) >> 1;
+            b = e - b;
+            c = e - c;
+            a -= c;
+            d += b;
+
+            output[column] = a * 4;
+            output[4 + column] = c * 4;
+            output[8 + column] = d * 4;
+            output[12 + column] = b * 4;
+        }
+
+        // Encoder coefficient storage is row-major, so exchange the reference walk's final frequency axes.
+        (output[1], output[4]) = (output[4], output[1]);
+        (output[2], output[8]) = (output[8], output[2]);
+        (output[3], output[12]) = (output[12], output[3]);
+        (output[6], output[9]) = (output[9], output[6]);
+        (output[7], output[13]) = (output[13], output[7]);
+        (output[11], output[14]) = (output[14], output[11]);
+    }
+
     /// <summary>
     /// Exercises every DCT, ADST, and identity stage network using both Int16 and Int32 lane arithmetic.
     /// </summary>

tests/ImageSharp.Tests/Formats/Heif/Av1/Av1TransformBlockEncoderTests.cs

@@ -626,6 +626,7 @@ public class Av1TransformBlockEncoderTests
             Assert.Equal(Av1EncoderModeDecisionWorkspace<ushort>.MaximumTransformSampleCount, modeWorkspace.Prediction.Length);
             Assert.Equal(Av1EncoderModeDecisionWorkspace<ushort>.MaximumTransformSampleCount, modeWorkspace.Residual.Length);
             Assert.Equal(Av1EncoderModeDecisionWorkspace<ushort>.MaximumCandidateTransformBlockCount, modeWorkspace.CandidateTransformBlocks.Length);
+            Assert.Equal(2048, modeWorkspace.CandidateTransformBlocks.Length);
 
             // CfL is unavailable above 32x32, so its scratch remains fixed while larger partitions are enabled.
             Assert.Equal(Av1ChromaFromLumaContext.BufferLength, modeWorkspace.ChromaFromLumaSamples.Length);

tests/ImageSharp.Tests/Formats/Heif/HeifEncoderTests.cs

@@ -8,6 +8,7 @@ using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Heif;
 using SixLabors.ImageSharp.Formats.Heif.Av1;
 using SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
+using SixLabors.ImageSharp.Formats.Heif.Av1.Transform;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Cicp;
@@ -181,18 +182,69 @@ public class HeifEncoderTests
     }
 
     [Fact]
-    public void Av1RejectsLosslessEncodingBeforeWritingOutput()
+    public void Av1LosslessRoundTripPreservesColorAndAlpha()
     {
-        using Image<Rgba32> image = new(1, 1);
+        const int width = 8;
+        const int height = 8;
+        using Image<Rgba32> image = new(width, height);
+        for (int row = 0; row < height; row++)
+        {
+            Span<Rgba32> pixels = image.Frames.RootFrame.PixelBuffer.DangerousGetRowSpan(row);
+            for (int column = 0; column < width; column++)
+            {
+                pixels[column] = new Rgba32(
+                    (byte)((column * 31) + row),
+                    (byte)((row * 29) + column),
+                    (byte)((column * 17) + (row * 11)),
+                    (byte)((column * 23) + (row * 7)));
+            }
+        }
+
+        // Identity-matrix 4:4:4 maps the packed RGB channels directly onto AV1 planes, so codec losslessness
+        // can be asserted against the original pixels without a separate color-conversion tolerance.
+        image.Metadata.CicpProfile = new CicpProfile(1, 13, 0, true);
         using MemoryStream stream = new();
         HeifEncoder encoder = new()
         {
             CompressionMethod = HeifCompressionMethod.Av1,
-            Lossless = true
+            Lossless = true,
+            Effort = 0
         };
 
-        Assert.Throws<NotSupportedException>(() => image.Save(stream, encoder));
-        Assert.Equal(0, stream.Length);
+        image.Save(stream, encoder);
+        byte[] file = stream.ToArray();
+        Span<byte> colorPayload = GetItemPayload(file, 1);
+        using Av1Decoder colorDecoder = new(Configuration.Default);
+        using Image<Rgba32> colorImage = colorDecoder.Decode<Rgba32>(colorPayload);
+        ObuSequenceHeader colorSequenceHeader = Assert.IsType<ObuSequenceHeader>(colorDecoder.SequenceHeader);
+        ObuFrameHeader colorFrameHeader = Assert.IsType<ObuFrameHeader>(colorDecoder.FrameHeader);
+
+        Assert.Equal(Av1ColorFormat.Yuv444, colorSequenceHeader.ColorConfig.GetColorFormat());
+        Assert.Equal(0, colorFrameHeader.QuantizationParameters.BaseQIndex);
+        Assert.True(colorFrameHeader.CodedLossless);
+        Assert.True(colorFrameHeader.AllLossless);
+        Assert.Equal(Av1TransformMode.Only4x4, colorFrameHeader.TransformMode);
+
+        Span<byte> alphaPayload = GetItemPayload(file, 2);
+        using Av1Decoder alphaDecoder = new(Configuration.Default);
+        using Image<L8> alphaImage = alphaDecoder.Decode<L8>(alphaPayload);
+        ObuFrameHeader alphaFrameHeader = Assert.IsType<ObuFrameHeader>(alphaDecoder.FrameHeader);
+        Assert.Equal(0, alphaFrameHeader.QuantizationParameters.BaseQIndex);
+        Assert.True(alphaFrameHeader.CodedLossless);
+
+        stream.Position = 0;
+        using Image<Rgba32> decoded = Image.Load<Rgba32>(stream);
+        Assert.Empty(ImageComparer.Exact.CompareImages(image, decoded));
+
+        string outputDirectory = Path.Combine(
+            TestEnvironment.ActualOutputDirectoryFullPath,
+            "Formats",
+            "Heif",
+            "Av1");
+
+        Directory.CreateDirectory(outputDirectory);
+        File.WriteAllBytes(Path.Combine(outputDirectory, "encoder-public-lossless-color.obu"), colorPayload.ToArray());
+        File.WriteAllBytes(Path.Combine(outputDirectory, "encoder-public-lossless-alpha.obu"), alphaPayload.ToArray());
     }
 
     [Fact]