mirror of https://github.com/SixLabors/ImageSharp
James Jackson-South
2 months ago
3 changed files with 140 additions and 1 deletions
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// Copyright (c) Six Labors.
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// Licensed under the Six Labors Split License.
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using SixLabors.ImageSharp.Memory; |
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namespace SixLabors.ImageSharp.Formats.Heif.Hevc; |
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/// <summary>
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/// Owns the native-precision luma and chroma sample planes for one reconstructed HEVC still picture.
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/// </summary>
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internal sealed class HevcPictureBuffer : IDisposable |
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{ |
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/// <summary>The horizontal chroma subsampling shift.</summary>
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private readonly int chromaSubsamplingX; |
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/// <summary>The vertical chroma subsampling shift.</summary>
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private readonly int chromaSubsamplingY; |
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/// <summary>
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/// Initializes a new instance of the <see cref="HevcPictureBuffer"/> class.
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/// </summary>
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/// <param name="configuration">The configuration providing the image memory allocator.</param>
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/// <param name="sequenceParameterSet">The coded dimensions, precision, and chroma layout.</param>
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public HevcPictureBuffer(Configuration configuration, HevcSequenceParameterSet sequenceParameterSet) |
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{ |
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this.Width = sequenceParameterSet.Width; |
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this.Height = sequenceParameterSet.Height; |
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this.BitDepthLuma = sequenceParameterSet.BitDepthLuma; |
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this.BitDepthChroma = sequenceParameterSet.BitDepthChroma; |
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this.ChromaFormat = sequenceParameterSet.ChromaFormat; |
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this.SeparateColorPlane = sequenceParameterSet.SeparateColorPlaneFlag; |
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// Separate color planes are independently coded at full resolution even though chroma_format_idc is 4:4:4.
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this.chromaSubsamplingX = !this.SeparateColorPlane && this.ChromaFormat is 1 or 2 ? 1 : 0; |
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this.chromaSubsamplingY = !this.SeparateColorPlane && this.ChromaFormat == 1 ? 1 : 0; |
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this.Luma = configuration.MemoryAllocator.Allocate2D<ushort>(this.Width, this.Height); |
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if (this.ChromaFormat != 0) |
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{ |
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int chromaWidth = DivideCeilingByPowerOfTwo(this.Width, this.chromaSubsamplingX); |
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int chromaHeight = DivideCeilingByPowerOfTwo(this.Height, this.chromaSubsamplingY); |
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this.ChromaBlue = configuration.MemoryAllocator.Allocate2D<ushort>(chromaWidth, chromaHeight); |
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this.ChromaRed = configuration.MemoryAllocator.Allocate2D<ushort>(chromaWidth, chromaHeight); |
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} |
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} |
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/// <summary>Gets the coded luma width in samples.</summary>
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public int Width { get; } |
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/// <summary>Gets the coded luma height in samples.</summary>
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public int Height { get; } |
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/// <summary>Gets the luma sample precision in bits.</summary>
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public int BitDepthLuma { get; } |
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/// <summary>Gets the chroma sample precision in bits.</summary>
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public int BitDepthChroma { get; } |
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/// <summary>Gets the HEVC chroma-format identifier.</summary>
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public byte ChromaFormat { get; } |
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/// <summary>Gets a value indicating whether the three planes are coded as independent full-resolution color planes.</summary>
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public bool SeparateColorPlane { get; } |
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/// <summary>Gets the luma or first separate-color-plane allocation.</summary>
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public Buffer2D<ushort> Luma { get; } |
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/// <summary>Gets the blue-difference chroma or second separate-color-plane allocation.</summary>
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public Buffer2D<ushort>? ChromaBlue { get; } |
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/// <summary>Gets the red-difference chroma or third separate-color-plane allocation.</summary>
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public Buffer2D<ushort>? ChromaRed { get; } |
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/// <summary>Gets the horizontal chroma subsampling shift for the selected plane.</summary>
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/// <param name="plane">The reconstruction plane.</param>
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/// <returns>Zero for luma and full-resolution planes; otherwise, the chroma shift.</returns>
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public int GetSubsamplingX(HevcPlane plane) => plane == HevcPlane.Y ? 0 : this.chromaSubsamplingX; |
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/// <summary>Gets the vertical chroma subsampling shift for the selected plane.</summary>
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/// <param name="plane">The reconstruction plane.</param>
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/// <returns>Zero for luma and full-resolution planes; otherwise, the chroma shift.</returns>
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public int GetSubsamplingY(HevcPlane plane) => plane == HevcPlane.Y ? 0 : this.chromaSubsamplingY; |
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/// <summary>Gets the selected plane width in samples.</summary>
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/// <param name="plane">The reconstruction plane.</param>
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/// <returns>The coded plane width.</returns>
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public int GetWidth(HevcPlane plane) => DivideCeilingByPowerOfTwo(this.Width, this.GetSubsamplingX(plane)); |
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/// <summary>Gets the selected plane height in samples.</summary>
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/// <param name="plane">The reconstruction plane.</param>
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/// <returns>The coded plane height.</returns>
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public int GetHeight(HevcPlane plane) => DivideCeilingByPowerOfTwo(this.Height, this.GetSubsamplingY(plane)); |
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/// <summary>Gets one coded row from the selected reconstruction plane.</summary>
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/// <param name="plane">The reconstruction plane.</param>
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/// <param name="row">The zero-based row index in plane samples.</param>
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/// <returns>The complete coded plane row.</returns>
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public Span<ushort> GetRowSpan(HevcPlane plane, int row) |
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=> plane switch |
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{ |
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HevcPlane.Y => this.Luma.DangerousGetRowSpan(row), |
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HevcPlane.Cb => this.ChromaBlue!.DangerousGetRowSpan(row), |
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_ => this.ChromaRed!.DangerousGetRowSpan(row), |
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}; |
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/// <summary>Releases the owned luma and chroma plane allocations.</summary>
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public void Dispose() |
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{ |
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this.Luma.Dispose(); |
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this.ChromaBlue?.Dispose(); |
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this.ChromaRed?.Dispose(); |
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} |
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/// <summary>Divides a nonnegative sample count by a power of two with upward rounding.</summary>
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/// <param name="value">The sample count.</param>
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/// <param name="shift">The base-two divisor logarithm.</param>
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/// <returns>The upward-rounded quotient.</returns>
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private static int DivideCeilingByPowerOfTwo(int value, int shift) => (value + (1 << shift) - 1) >> shift; |
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} |
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@ -0,0 +1,19 @@ |
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// Copyright (c) Six Labors.
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// Licensed under the Six Labors Split License.
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namespace SixLabors.ImageSharp.Formats.Heif.Hevc; |
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/// <summary>
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/// Identifies an HEVC luma or chroma reconstruction plane.
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/// </summary>
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internal enum HevcPlane |
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{ |
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/// <summary>The luma or first separate-color plane.</summary>
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Y = 0, |
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/// <summary>The blue-difference chroma or second separate-color plane.</summary>
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Cb = 1, |
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/// <summary>The red-difference chroma or third separate-color plane.</summary>
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Cr = 2, |
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} |
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