@ -2,43 +2,158 @@
// Licensed under the Six Labors Split License.
using SixLabors.ImageSharp.Formats.Heif.Av1.Prediction ;
using SixLabors.ImageSharp.Formats.Heif.Av1.Prediction.ChromaFromLuma ;
using SixLabors.ImageSharp.Formats.Heif.Av1.Tiling ;
using SixLabors.ImageSharp.Formats.Heif.Av1.Transform ;
namespace SixLabors.ImageSharp.Formats.Heif.Av1.Entropy ;
/// <summary>
/// Decodes tile syntax elements and transform coefficients from an AV1 entropy-coded bitstream.
/// </summary>
internal ref struct Av1SymbolDecoder
{
/// <summary>
/// Maps each intra prediction mode to the reduced neighbor context used by key-frame luma modes.
/// </summary>
private static readonly int [ ] IntraModeContext = [ 0 , 1 , 2 , 3 , 4 , 4 , 4 , 4 , 3 , 0 , 1 , 2 , 0 ] ;
private static readonly int [ ] AlphaVContexts = [ - 1 , 0 , 3 , - 1 , 1 , 4 , - 1 , 2 , 5 ] ;
/// <summary>
/// The tile-adaptive intra-block-copy distribution.
/// </summary>
private readonly Av1Distribution tileIntraBlockCopy = Av1DefaultDistributions . IntraBlockCopy ;
/// <summary>
/// The tile-adaptive partition-type distributions.
/// </summary>
private readonly Av1Distribution [ ] tilePartitionTypes = Av1DefaultDistributions . PartitionTypes ;
/// <summary>
/// The tile-adaptive key-frame luma-mode distributions.
/// </summary>
private readonly Av1Distribution [ ] [ ] keyFrameYMode = Av1DefaultDistributions . KeyFrameYMode ;
/// <summary>
/// The tile-adaptive chroma intra-mode distributions.
/// </summary>
private readonly Av1Distribution [ ] [ ] uvMode = Av1DefaultDistributions . UvMode ;
/// <summary>
/// The tile-adaptive transform-skip distributions.
/// </summary>
private readonly Av1Distribution [ ] skip = Av1DefaultDistributions . Skip ;
/// <summary>
/// The tile-adaptive skip-mode distributions.
/// </summary>
private readonly Av1Distribution [ ] skipMode = Av1DefaultDistributions . SkipMode ;
/// <summary>
/// The tile-adaptive absolute loop-filter delta distribution.
/// </summary>
private readonly Av1Distribution deltaLoopFilterAbsolute = Av1DefaultDistributions . DeltaLoopFilterAbsolute ;
/// <summary>
/// The tile-adaptive absolute quantizer delta distribution.
/// </summary>
private readonly Av1Distribution deltaQuantizerAbsolute = Av1DefaultDistributions . DeltaQuantizerAbsolute ;
/// <summary>
/// The tile-adaptive spatial segment-identifier distributions.
/// </summary>
private readonly Av1Distribution [ ] segmentId = Av1DefaultDistributions . SegmentId ;
/// <summary>
/// The tile-adaptive directional angle-delta distributions.
/// </summary>
private readonly Av1Distribution [ ] angleDelta = Av1DefaultDistributions . AngleDelta ;
/// <summary>
/// The tile-adaptive filter-intra mode distribution.
/// </summary>
private readonly Av1Distribution filterIntraMode = Av1DefaultDistributions . FilterIntraMode ;
/// <summary>
/// The tile-adaptive filter-intra enable distributions.
/// </summary>
private readonly Av1Distribution [ ] filterIntra = Av1DefaultDistributions . FilterIntra ;
/// <summary>
/// The tile-adaptive transform-size distributions.
/// </summary>
private readonly Av1Distribution [ ] [ ] transformSize = Av1DefaultDistributions . TransformSize ;
/// <summary>
/// The tile-adaptive end-of-block token distributions selected for the frame base quantizer.
/// </summary>
private readonly Av1Distribution [ ] [ ] [ ] endOfBlockFlag ;
/// <summary>
/// The tile-adaptive coefficient base-level distributions selected for the frame base quantizer.
/// </summary>
private readonly Av1Distribution [ ] [ ] [ ] coefficientsBase ;
/// <summary>
/// The tile-adaptive final-nonzero coefficient distributions selected for the frame base quantizer.
/// </summary>
private readonly Av1Distribution [ ] [ ] [ ] baseEndOfBlock ;
/// <summary>
/// The tile-adaptive DC sign distributions selected for the frame base quantizer.
/// </summary>
private readonly Av1Distribution [ ] [ ] dcSign ;
/// <summary>
/// The tile-adaptive coefficient base-range distributions selected for the frame base quantizer.
/// </summary>
private readonly Av1Distribution [ ] [ ] [ ] coefficientsBaseRange ;
/// <summary>
/// The tile-adaptive transform-block skip distributions selected for the frame base quantizer.
/// </summary>
private readonly Av1Distribution [ ] [ ] transformBlockSkip ;
/// <summary>
/// The tile-adaptive end-of-block extra-bit distributions selected for the frame base quantizer.
/// </summary>
private readonly Av1Distribution [ ] [ ] [ ] endOfBlockExtra ;
/// <summary>
/// The tile-adaptive joint chroma-from-luma sign distribution.
/// </summary>
private readonly Av1Distribution chromaFromLumaSign = Av1DefaultDistributions . ChromaFromLumaSign ;
/// <summary>
/// The tile-adaptive chroma-from-luma alpha-magnitude distributions.
/// </summary>
private readonly Av1Distribution [ ] chromaFromLumaAlpha = Av1DefaultDistributions . ChromaFromLumaAlpha ;
/// <summary>
/// The tile-adaptive intra transform-type distributions.
/// </summary>
private readonly Av1Distribution [ ] [ ] [ ] intraExtendedTransform = Av1DefaultDistributions . IntraExtendedTransform ;
/// <summary>
/// The configuration providing temporary coefficient-context memory.
/// </summary>
private readonly Configuration configuration ;
/// <summary>
/// The range decoder over the current tile payload.
/// </summary>
private Av1SymbolReader reader ;
/// <summary>
/// The frame base quantizer used to select coefficient probability models.
/// </summary>
private readonly int baseQIndex ;
/// <summary>
/// Initializes a new instance of the <see cref="Av1SymbolDecoder"/> struct for one AV1 tile.
/// </summary>
/// <param name="configuration">The configuration providing temporary memory.</param>
/// <param name="tileData">The entropy-coded tile payload.</param>
/// <param name="qIndex">The frame base quantizer index.</param>
public Av1SymbolDecoder ( Configuration configuration , Span < byte > tileData , int qIndex )
{
this . configuration = configuration ;
@ -53,18 +168,32 @@ internal ref struct Av1SymbolDecoder
this . endOfBlockExtra = Av1DefaultDistributions . GetEndOfBlockExtra ( qIndex ) ;
}
/// <summary>
/// Reads a fixed-width CDEF strength index.
/// </summary>
/// <param name="bitCount">The number of bits signaled for the strength index.</param>
/// <returns>The decoded CDEF strength index.</returns>
public int ReadCdfStrength ( int bitCount )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadLiteral ( bitCount ) ;
}
/// <summary>
/// Reads the frame-local intra-block-copy flag.
/// </summary>
/// <returns><see langword="true"/> when intra-block copy is selected.</returns>
public bool ReadUseIntraBlockCopy ( )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . tileIntraBlockCopy ) > 0 ;
}
/// <summary>
/// Reads a complete block partition type from the selected partition context.
/// </summary>
/// <param name="context">The partition probability context.</param>
/// <returns>The decoded partition type.</returns>
public Av1PartitionType ReadPartitionType ( int context )
{
ref Av1SymbolReader r = ref this . reader ;
@ -72,8 +201,11 @@ internal ref struct Av1SymbolDecoder
}
/// <summary>
/// SVT: partition_gather_vert_alike
/// Reads the binary split-versus-horizontal decision used at a clipped right tile boundary.
/// </summary>
/// <param name="blockSize">The current block size.</param>
/// <param name="context">The partition probability context.</param>
/// <returns><see cref="Av1PartitionType.Split"/> or <see cref="Av1PartitionType.Horizontal"/>.</returns>
public Av1PartitionType ReadSplitOrHorizontal ( Av1BlockSize blockSize , int context )
{
Av1Distribution distribution = GetSplitOrHorizontalDistribution ( this . tilePartitionTypes , blockSize , context ) ;
@ -82,8 +214,11 @@ internal ref struct Av1SymbolDecoder
}
/// <summary>
/// SVT: partition_gather_horz_alike
/// Reads the binary split-versus-vertical decision used at a clipped bottom tile boundary.
/// </summary>
/// <param name="blockSize">The current block size.</param>
/// <param name="context">The partition probability context.</param>
/// <returns><see cref="Av1PartitionType.Split"/> or <see cref="Av1PartitionType.Vertical"/>.</returns>
public Av1PartitionType ReadSplitOrVertical ( Av1BlockSize blockSize , int context )
{
Av1Distribution distribution = GetSplitOrVerticalDistribution ( this . tilePartitionTypes , blockSize , context ) ;
@ -91,6 +226,12 @@ internal ref struct Av1SymbolDecoder
return r . ReadSymbol ( distribution ) > 0 ? Av1PartitionType . Split : Av1PartitionType . Vertical ;
}
/// <summary>
/// Reads a key-frame luma prediction mode using the available above and left modes.
/// </summary>
/// <param name="aboveModeInfo">The above block mode, or <see langword="null"/> at the frame boundary.</param>
/// <param name="leftModeInfo">The left block mode, or <see langword="null"/> at the frame boundary.</param>
/// <returns>The decoded luma prediction mode.</returns>
public Av1PredictionMode ReadYMode ( Av1BlockModeInfo ? aboveModeInfo , Av1BlockModeInfo ? leftModeInfo )
{
ref Av1SymbolReader r = ref this . reader ;
@ -111,6 +252,12 @@ internal ref struct Av1SymbolDecoder
return ( Av1PredictionMode ) r . ReadSymbol ( this . keyFrameYMode [ aboveContext ] [ leftContext ] ) ;
}
/// <summary>
/// Reads a chroma intra prediction mode conditioned on the luma mode and chroma-from-luma availability.
/// </summary>
/// <param name="mode">The decoded luma prediction mode.</param>
/// <param name="chromaFromLumaAllowed">Indicates whether chroma-from-luma is valid for the block.</param>
/// <returns>The decoded chroma prediction mode.</returns>
public Av1PredictionMode ReadIntraModeUv ( Av1PredictionMode mode , bool chromaFromLumaAllowed )
{
int chromaForLumaIndex = chromaFromLumaAllowed ? 1 : 0 ;
@ -118,18 +265,32 @@ internal ref struct Av1SymbolDecoder
return ( Av1PredictionMode ) r . ReadSymbol ( this . uvMode [ chromaForLumaIndex ] [ ( int ) mode ] ) ;
}
/// <summary>
/// Reads the transform-skip flag from a neighboring skip context.
/// </summary>
/// <param name="ctx">The neighboring skip context.</param>
/// <returns><see langword="true"/> when the block contains no coded transform coefficients.</returns>
public bool ReadSkip ( int ctx )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . skip [ ctx ] ) > 0 ;
}
public bool ReadSkipMode ( Av1BlockSize blockSize )
/// <summary>
/// Reads the compound-reference skip-mode flag.
/// </summary>
/// <param name="context">The neighboring skip-mode context.</param>
/// <returns><see langword="true"/> when skip mode is selected.</returns>
public bool ReadSkipMode ( int context )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . skipMode [ ( int ) blockSize ] ) > 0 ;
return r . ReadSymbol ( this . skipMode [ context ] ) > 0 ;
}
/// <summary>
/// Reads a signed loop-filter delta value.
/// </summary>
/// <returns>The decoded loop-filter delta.</returns>
public int ReadDeltaLoopFilter ( )
{
ref Av1SymbolReader r = ref this . reader ;
@ -151,8 +312,9 @@ internal ref struct Av1SymbolDecoder
}
/// <summary>
/// SVT: read_delta_qindex
/// Reads a signed quantizer-index delta value.
/// </summary>
/// <returns>The decoded quantizer-index delta.</returns>
public int ReadDeltaQuantizerIndex ( )
{
ref Av1SymbolReader r = ref this . reader ;
@ -173,18 +335,33 @@ internal ref struct Av1SymbolDecoder
return deltaQuantizerSignBit ? - deltaQuantizerAbsolute : deltaQuantizerAbsolute ;
}
/// <summary>
/// Reads a spatially predicted segment identifier.
/// </summary>
/// <param name="context">The context derived from neighboring segment identifiers.</param>
/// <returns>The decoded segment identifier.</returns>
public int ReadSegmentId ( int context )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . segmentId [ context ] ) ;
}
/// <summary>
/// Reads the unsigned directional angle-delta symbol for a prediction mode.
/// </summary>
/// <param name="mode">The directional prediction mode.</param>
/// <returns>The symbol in the range zero through twice the maximum signed angle delta.</returns>
public int ReadAngleDelta ( Av1PredictionMode mode )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . angleDelta [ ( int ) mode - 1 ] ) ;
}
/// <summary>
/// Reads the filter-intra enable flag and, when enabled, its prediction mode.
/// </summary>
/// <param name="blockSize">The block size selecting the enable distribution.</param>
/// <returns>The selected mode, or <see cref="Av1FilterIntraMode.AllFilterIntraModes"/> when filter-intra is disabled.</returns>
public Av1FilterIntraMode ReadFilterUltraMode ( Av1BlockSize blockSize )
{
ref Av1SymbolReader r = ref this . reader ;
@ -198,6 +375,12 @@ internal ref struct Av1SymbolDecoder
return filterIntraMode ;
}
/// <summary>
/// Reads a transform subdivision depth and resolves it to a transform size.
/// </summary>
/// <param name="blockSize">The block size defining the maximum transform.</param>
/// <param name="context">The neighboring transform-size context.</param>
/// <returns>The decoded transform size.</returns>
public Av1TransformSize ReadTransformSize ( Av1BlockSize blockSize , int context )
{
ref Av1SymbolReader r = ref this . reader ;
@ -223,8 +406,15 @@ internal ref struct Av1SymbolDecoder
}
/// <summary>
/// SVT: parse_transform_type
/// Reads an intra transform type from the transform set permitted for the block.
/// </summary>
/// <param name="transformSize">The coded transform size.</param>
/// <param name="useReducedTransformSet">Indicates whether the frame restricts transform choices.</param>
/// <param name="useFilterIntra">Indicates whether filter-intra prediction selected the intra direction.</param>
/// <param name="baseQIndex">The active base quantizer index.</param>
/// <param name="filterIntraMode">The filter-intra mode when enabled.</param>
/// <param name="intraDirection">The ordinary intra prediction mode.</param>
/// <returns>The decoded transform type, or DCT-DCT when no transform type is signaled.</returns>
public Av1TransformType ReadTransformType (
Av1TransformSize transformSize ,
bool useReducedTransformSet ,
@ -235,20 +425,13 @@ internal ref struct Av1SymbolDecoder
{
Av1TransformType transformType = Av1TransformType . DctDct ;
/ *
// No need to read transform type if block is skipped.
if ( mbmi . Skip | |
svt_aom_seg_feature_active ( & parse_ctxt - > frame_header - > segmentation_params , mbmi - > segment_id , SEG_LVL_SKIP ) )
return ;
* /
// A zero base quantizer selects DCT-DCT and carries no transform-type symbol in this intra path.
if ( baseQIndex = = 0 )
{
return transformType ;
}
// Ignoring INTER blocks here, as these should not end up here.
// int inter_block = is_inter_block_dec(mbmi);
// Still-image decoding reaches this path only for intra blocks, so the intra transform set is authoritative.
Av1TransformSetType transformSetType = Av1SymbolContextHelper . GetExtendedTransformSetType ( transformSize , useReducedTransformSet ) ;
if ( transformSetType > Av1TransformSetType . DctOnly & & baseQIndex > 0 )
{
@ -265,35 +448,73 @@ internal ref struct Av1SymbolDecoder
return transformType ;
}
/// <summary>
/// Reads whether a transform block has no coded coefficients.
/// </summary>
/// <param name="transformSizeContext">The square transform-size probability context.</param>
/// <param name="skipContext">The context derived from neighboring coefficient blocks.</param>
/// <returns><see langword="true"/> when the transform block is empty.</returns>
public bool ReadTransformBlockSkip ( Av1TransformSize transformSizeContext , int skipContext )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . transformBlockSkip [ ( int ) transformSizeContext ] [ skipContext ] ) > 0 ;
}
/// <summary>
/// Reads the joint U/V sign symbol for chroma-from-luma alpha values.
/// </summary>
/// <returns>The joint sign symbol.</returns>
public int ReadChromFromLumaSign ( )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . chromaFromLumaSign ) ;
}
/// <summary>
/// Reads the U-plane chroma-from-luma alpha-magnitude symbol.
/// </summary>
/// <param name="jointSignPlus1">The one-based joint U/V sign symbol.</param>
/// <returns>The U-plane alpha-magnitude symbol.</returns>
public int ReadChromaFromLumaAlphaU ( int jointSignPlus1 )
{
ref Av1SymbolReader r = ref this . reader ;
int context = jointSignPlus1 - 3 ;
int context = Av1ChromaFromLumaMath . ContextU ( jointSignPlus1 - 1 ) ;
return r . ReadSymbol ( this . chromaFromLumaAlpha [ context ] ) ;
}
/// <summary>
/// Reads the V-plane chroma-from-luma alpha-magnitude symbol.
/// </summary>
/// <param name="jointSignPlus1">The one-based joint U/V sign symbol.</param>
/// <returns>The V-plane alpha-magnitude symbol.</returns>
public int ReadChromaFromLumaAlphaV ( int jointSignPlus1 )
{
ref Av1SymbolReader r = ref this . reader ;
int context = AlphaVContexts [ jointSignPlus1 ] ;
int context = Av1ChromaFromLumaMath . ContextV ( jointSignPlus1 - 1 ) ;
return r . ReadSymbol ( this . chromaFromLumaAlpha [ context ] ) ;
}
/// <summary>
/// SVT: parse_coeffs
/// Decodes one transform block's coefficient syntax and updates its neighboring entropy contexts.
/// </summary>
/// <param name="modeInfo">The current block prediction and segment modes.</param>
/// <param name="blockPosition">The transform-block position in four-sample units.</param>
/// <param name="aboveContexts">The above coefficient contexts for the current plane.</param>
/// <param name="leftContexts">The left coefficient contexts for the current plane.</param>
/// <param name="aboveOffset">The first above context covered by the transform.</param>
/// <param name="leftOffset">The first left context covered by the transform.</param>
/// <param name="plane">The zero-based Y, U, or V plane index.</param>
/// <param name="blocksWide">The available plane width in four-sample units.</param>
/// <param name="blocksHigh">The available plane height in four-sample units.</param>
/// <param name="transformBlockContext">The neighboring skip and DC sign contexts.</param>
/// <param name="transformSize">The signaled transform size.</param>
/// <param name="isLossless">Indicates whether the active segment is lossless.</param>
/// <param name="useReducedTransformSet">Indicates whether the frame restricts transform choices.</param>
/// <param name="transformInfo">The transform descriptor updated with the decoded type and coded-block flag.</param>
/// <param name="modeBlocksToRightEdge">The signed distance from the mode block to the right frame edge.</param>
/// <param name="modeBlocksToBottomEdge">The signed distance from the mode block to the bottom frame edge.</param>
/// <param name="coefficientBuffer">The destination receiving the coefficient count followed by scan-ordered signed levels.</param>
/// <returns>The one-based end-of-block position, or zero for an empty transform block.</returns>
public int ReadCoefficients (
Av1BlockModeInfo modeInfo ,
Point blockPosition ,
@ -313,13 +534,15 @@ internal ref struct Av1SymbolDecoder
int modeBlocksToBottomEdge ,
Span < int > coefficientBuffer )
{
int width = transformSize . GetWidth ( ) ;
int height = transformSize . GetHeight ( ) ;
Av1TransformSize adjustedTransformSize = transformSize . GetAdjusted ( ) ;
int width = adjustedTransformSize . GetWidth ( ) ;
int height = adjustedTransformSize . GetHeight ( ) ;
Av1TransformSize transformSizeContext = Av1SymbolContextHelper . GetTransformSizeContext ( transformSize ) ;
Av1PlaneType planeType = ( Av1PlaneType ) Math . Min ( plane , 1 ) ;
int culLevel = 0 ;
Av1LevelBuffer levels = new ( this . configuration , new Size ( width , height ) ) ;
// AV1 omits high-frequency coefficients beyond 32 samples on every 64-point transform dimension.
using Av1LevelBuffer levels = new ( this . configuration , new Size ( width , height ) ) ;
bool allZero = this . ReadTransformBlockSkip ( transformSizeContext , transformBlockContext . SkipContext ) ;
int endOfBlock ;
@ -373,6 +596,14 @@ internal ref struct Av1SymbolDecoder
return endOfBlock ;
}
/// <summary>
/// Reads an end-of-block token and its literal suffix.
/// </summary>
/// <param name="transformSize">The signaled transform size selecting the token alphabet.</param>
/// <param name="transformClass">The transform class selecting the two-dimensional or one-dimensional model.</param>
/// <param name="transformSizeContext">The square transform-size probability context.</param>
/// <param name="planeType">The luma or chroma plane category.</param>
/// <returns>The one-based end-of-block coefficient position.</returns>
public int ReadEndOfBlockPosition ( Av1TransformSize transformSize , Av1TransformClass transformClass , Av1TransformSize transformSizeContext , Av1PlaneType planeType )
{
ref Av1SymbolReader r = ref this . reader ;
@ -381,7 +612,8 @@ internal ref struct Av1SymbolDecoder
int endOfBlockShift = Av1SymbolContextHelper . EndOfBlockOffsetBits [ endOfBlockPoint ] ;
if ( endOfBlockShift > 0 )
{
int endOfBlockContext = endOfBlockPoint ;
// Extra-bit distributions start with token three because the first three tokens have no extra bits.
int endOfBlockContext = endOfBlockPoint - 3 ;
bool bit = this . ReadEndOfBlockExtra ( transformSizeContext , planeType , endOfBlockContext ) ;
if ( bit )
{
@ -400,13 +632,21 @@ internal ref struct Av1SymbolDecoder
return Av1SymbolContextHelper . RecordEndOfBlockPosition ( endOfBlockPoint , endOfBlockExtra ) ;
}
/// <summary>
/// Decodes the mandatory nonzero coefficient at the end-of-block scan position.
/// </summary>
/// <param name="transformClass">The transform direction class.</param>
/// <param name="endOfBlock">The one-based end-of-block position.</param>
/// <param name="scan">The transform's scan-to-raster mapping.</param>
/// <param name="levels">The padded absolute-coefficient level plane to update.</param>
/// <param name="transformSizeContext">The square transform-size probability context.</param>
/// <param name="planeType">The luma or chroma plane category.</param>
public void ReadCoefficientsEndOfBlock ( Av1TransformClass transformClass , int endOfBlock , ReadOnlySpan < short > scan , Av1LevelBuffer levels , Av1TransformSize transformSizeContext , Av1PlaneType planeType )
{
int i = endOfBlock - 1 ;
Point position = levels . GetPosition ( scan [ i ] ) ;
int coefficientContext = Av1SymbolContextHelper . GetLowerLevelContextEndOfBlock ( levels , position ) ;
int coefficientContext = Av1SymbolContextHelper . GetLowerLevelContextEndOfBlock ( levels , i ) ;
int level = this . ReadBaseEndOfBlock ( transformSizeContext , planeType , coefficientContext ) + 1 ;
Av1TransformSize limitedTransformSizeContext = ( Av1TransformSize ) Math . Min ( ( int ) transformSizeContext , ( int ) Av1TransformSize . Size32x32 ) ;
if ( level > Av1Constants . BaseLevelsCount )
{
int baseRangeContext = Av1SymbolContextHelper . GetBaseRangeContextEndOfBlock ( position , transformClass ) ;
@ -416,9 +656,18 @@ internal ref struct Av1SymbolDecoder
levels . GetRow ( position ) [ position . X ] = ( byte ) level ;
}
/// <summary>
/// Decodes a reverse scan range using the specialized two-dimensional coefficient contexts.
/// </summary>
/// <param name="transformSize">The signaled transform size.</param>
/// <param name="startScanIndex">The inclusive lowest scan index.</param>
/// <param name="endScanIndex">The inclusive highest scan index.</param>
/// <param name="scan">The transform's scan-to-raster mapping.</param>
/// <param name="levels">The padded absolute-coefficient level plane to update.</param>
/// <param name="transformSizeContext">The square transform-size probability context.</param>
/// <param name="planeType">The luma or chroma plane category.</param>
public void ReadCoefficientsReverse2d ( Av1TransformSize transformSize , int startScanIndex , int endScanIndex , ReadOnlySpan < short > scan , Av1LevelBuffer levels , Av1TransformSize transformSizeContext , Av1PlaneType planeType )
{
Av1TransformSize limitedTransformSizeContext = ( Av1TransformSize ) Math . Min ( ( int ) transformSizeContext , ( int ) Av1TransformSize . Size32x32 ) ;
for ( int c = endScanIndex ; c > = startScanIndex ; - - c )
{
Point position = levels . GetPosition ( scan [ c ] ) ;
@ -434,9 +683,19 @@ internal ref struct Av1SymbolDecoder
}
}
/// <summary>
/// Decodes a reverse scan range using transform-class-specific coefficient contexts.
/// </summary>
/// <param name="transformSize">The signaled transform size.</param>
/// <param name="transformClass">The transform direction class.</param>
/// <param name="startScanIndex">The inclusive lowest scan index.</param>
/// <param name="endScanIndex">The inclusive highest scan index.</param>
/// <param name="scan">The transform's scan-to-raster mapping.</param>
/// <param name="levels">The padded absolute-coefficient level plane to update.</param>
/// <param name="transformSizeContext">The square transform-size probability context.</param>
/// <param name="planeType">The luma or chroma plane category.</param>
public void ReadCoefficientsReverse ( Av1TransformSize transformSize , Av1TransformClass transformClass , int startScanIndex , int endScanIndex , ReadOnlySpan < short > scan , Av1LevelBuffer levels , Av1TransformSize transformSizeContext , Av1PlaneType planeType )
{
Av1TransformSize limitedTransformSizeContext = ( Av1TransformSize ) Math . Min ( ( int ) transformSizeContext , ( int ) Av1TransformSize . Size32x32 ) ;
for ( int c = endScanIndex ; c > = startScanIndex ; - - c )
{
int pos = scan [ c ] ;
@ -453,21 +712,30 @@ internal ref struct Av1SymbolDecoder
}
}
/// <summary>
/// Reads coefficient signs and Golomb extensions, then writes scan-ordered signed levels.
/// </summary>
/// <param name="coefficientBuffer">The destination receiving the coefficient count followed by signed levels.</param>
/// <param name="endOfBlock">The one-based end-of-block position and coefficient count.</param>
/// <param name="scan">The transform's scan-to-raster mapping.</param>
/// <param name="levels">The decoded absolute-coefficient level plane.</param>
/// <param name="dcSignContext">The neighboring DC sign context.</param>
/// <param name="planeType">The luma or chroma plane category.</param>
/// <returns>The packed coefficient context used by adjacent transform blocks.</returns>
public int ReadCoefficientsSign ( Span < int > coefficientBuffer , int endOfBlock , ReadOnlySpan < short > scan , Av1LevelBuffer levels , int dcSignContext , Av1PlaneType planeType )
{
ref Av1SymbolReader r = ref this . reader ;
int maxScanLine = 0 ;
int culLevel = 0 ;
int dcValue = 0 ;
coefficientBuffer [ 0 ] = endOfBlock ;
for ( int c = 0 ; c < endOfBlock ; c + + )
{
int sign = 0 ;
Point position = levels . GetPosition ( c ) ;
int pos = scan [ c ] ;
Point position = levels . GetPosition ( pos ) ;
int level = levels [ position ] ;
if ( level ! = 0 )
{
maxScanLine = Math . Max ( maxScanLine , scan [ c ] ) ;
if ( c = = 0 )
{
sign = this . ReadDcSign ( planeType , dcSignContext ) ;
@ -500,6 +768,13 @@ internal ref struct Av1SymbolDecoder
return culLevel ;
}
/// <summary>
/// Reads the end-of-block token for a transform coefficient-count category.
/// </summary>
/// <param name="planeType">The luma or chroma plane category.</param>
/// <param name="transformClass">The transform direction class.</param>
/// <param name="transformSize">The signaled transform size.</param>
/// <returns>The one-based end-of-block token.</returns>
private int ReadEndOfBlockFlag ( Av1PlaneType planeType , Av1TransformClass transformClass , Av1TransformSize transformSize )
{
int endOfBlockContext = transformClass = = Av1TransformClass . Class2D ? 0 : 1 ;
@ -508,36 +783,77 @@ internal ref struct Av1SymbolDecoder
return r . ReadSymbol ( this . endOfBlockFlag [ endOfBlockMultiSize ] [ ( int ) planeType ] [ endOfBlockContext ] ) + 1 ;
}
/// <summary>
/// Reads the most significant context-coded bit of an end-of-block suffix.
/// </summary>
/// <param name="transformSizeContext">The square transform-size probability context.</param>
/// <param name="planeType">The luma or chroma plane category.</param>
/// <param name="endOfBlockContext">The zero-based extra-bit token context.</param>
/// <returns>The decoded suffix bit.</returns>
private bool ReadEndOfBlockExtra ( Av1TransformSize transformSizeContext , Av1PlaneType planeType , int endOfBlockContext )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . endOfBlockExtra [ ( int ) transformSizeContext ] [ ( int ) planeType ] [ endOfBlockContext ] ) > 0 ;
}
/// <summary>
/// Reads one coefficient base-range symbol.
/// </summary>
/// <param name="transformSizeContext">The square transform-size probability context.</param>
/// <param name="planeType">The luma or chroma plane category.</param>
/// <param name="baseRangeContext">The coefficient base-range context.</param>
/// <returns>The decoded base-range symbol.</returns>
private int ReadCoefficientsBaseRange ( Av1TransformSize transformSizeContext , Av1PlaneType planeType , int baseRangeContext )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . coefficientsBaseRange [ ( int ) transformSizeContext ] [ ( int ) planeType ] [ baseRangeContext ] ) ;
}
/// <summary>
/// Reads the sign of a nonzero DC coefficient.
/// </summary>
/// <param name="planeType">The luma or chroma plane category.</param>
/// <param name="dcSignContext">The neighboring DC sign context.</param>
/// <returns>Zero for positive or one for negative.</returns>
private int ReadDcSign ( Av1PlaneType planeType , int dcSignContext )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . dcSign [ ( int ) planeType ] [ dcSignContext ] ) ;
}
/// <summary>
/// Reads the base-level symbol for the final nonzero coefficient.
/// </summary>
/// <param name="transformSizeContext">The square transform-size probability context.</param>
/// <param name="planeType">The luma or chroma plane category.</param>
/// <param name="coefficientContext">The end-of-block coefficient context.</param>
/// <returns>The zero-based base-level symbol.</returns>
private int ReadBaseEndOfBlock ( Av1TransformSize transformSizeContext , Av1PlaneType planeType , int coefficientContext )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . baseEndOfBlock [ ( int ) transformSizeContext ] [ ( int ) planeType ] [ coefficientContext ] ) ;
}
/// <summary>
/// Reads the base-level symbol for a coefficient preceding end-of-block.
/// </summary>
/// <param name="transformSizeContext">The square transform-size probability context.</param>
/// <param name="planeType">The luma or chroma plane category.</param>
/// <param name="coefficientContext">The nonzero-map coefficient context.</param>
/// <returns>The decoded base-level symbol.</returns>
private int ReadCoefficientsBase ( Av1TransformSize transformSizeContext , Av1PlaneType planeType , int coefficientContext )
{
ref Av1SymbolReader r = ref this . reader ;
return r . ReadSymbol ( this . coefficientsBase [ ( int ) transformSizeContext ] [ ( int ) planeType ] [ coefficientContext ] ) ;
}
/// <summary>
/// Accumulates coefficient base-range symbols until the terminal symbol or AV1 range limit is reached.
/// </summary>
/// <param name="transformSizeContext">The square transform-size probability context.</param>
/// <param name="planeType">The luma or chroma plane category.</param>
/// <param name="baseRangeContext">The coefficient base-range context.</param>
/// <param name="level">The coefficient level to increment.</param>
private void ReadCoefficientsBaseRangeLoop ( Av1TransformSize transformSizeContext , Av1PlaneType planeType , int baseRangeContext , ref int level )
{
ref Av1SymbolReader r = ref this . reader ;
@ -554,6 +870,11 @@ internal ref struct Av1SymbolDecoder
}
}
/// <summary>
/// Reads the unsigned exponential-Golomb suffix used for coefficient levels beyond the base range.
/// </summary>
/// <returns>The decoded nonnegative suffix value.</returns>
/// <exception cref="InvalidImageContentException">The unary prefix exceeds the AV1 coefficient limit.</exception>
internal int ReadGolomb ( )
{
ref Av1SymbolReader r = ref this . reader ;
@ -567,8 +888,7 @@ internal ref struct Av1SymbolDecoder
+ + length ;
if ( length > 2 0 )
{
// SVT_LOG("Invalid length in read_golomb");
break ;
throw new InvalidImageContentException ( "The AV1 coefficient Golomb code exceeds its 20-bit limit." ) ;
}
}
@ -581,6 +901,21 @@ internal ref struct Av1SymbolDecoder
return x - 1 ;
}
/// <summary>
/// Stores a transform block's packed coefficient context into the above and left neighbor arrays.
/// </summary>
/// <param name="modeInfo">The current block mode information.</param>
/// <param name="aboveContexts">The above contexts for the current plane.</param>
/// <param name="leftContexts">The left contexts for the current plane.</param>
/// <param name="blocksWide">The available plane width in four-sample units.</param>
/// <param name="blocksHigh">The available plane height in four-sample units.</param>
/// <param name="transformSize">The signaled transform size.</param>
/// <param name="blockPosition">The transform-block position in four-sample units.</param>
/// <param name="aboveOffset">The first above context covered by the transform.</param>
/// <param name="leftOffset">The first left context covered by the transform.</param>
/// <param name="culLevel">The packed coefficient magnitude and DC sign context.</param>
/// <param name="modeBlockToRightEdge">The signed distance from the mode block to the right frame edge.</param>
/// <param name="modeBlockToBottomEdge">The signed distance from the mode block to the bottom frame edge.</param>
private static void UpdateCoefficientContext (
Av1BlockModeInfo modeInfo ,
int [ ] aboveContexts ,
@ -613,7 +948,7 @@ internal ref struct Av1SymbolDecoder
{
int leftContextCount = Math . Min ( transformSizeHigh , blocksHigh - leftOffset ) ;
Array . Fill ( leftContexts , culLevel , 0 , leftContextCount ) ;
Array . Fill ( leftContexts , 0 , leftContextCount , transformSizeWide - leftContextCount ) ;
Array . Fill ( leftContexts , 0 , leftContextCount , transformSizeHigh - leftContextCount ) ;
}
else
{
@ -621,6 +956,16 @@ internal ref struct Av1SymbolDecoder
}
}
/// <summary>
/// Resolves the transform type permitted for a plane after lossless, size, prediction, and transform-set restrictions.
/// </summary>
/// <param name="planeType">The luma or chroma plane category.</param>
/// <param name="modeInfo">The current block prediction modes.</param>
/// <param name="isLossless">Indicates whether the active segment is lossless.</param>
/// <param name="transformSize">The signaled transform size.</param>
/// <param name="transformInfo">The transform descriptor containing the signaled luma type.</param>
/// <param name="useReducedTransformSet">Indicates whether the frame restricts transform choices.</param>
/// <returns>The transform type valid for the current plane.</returns>
private static Av1TransformType ComputeTransformType ( Av1PlaneType planeType , Av1BlockModeInfo modeInfo , bool isLossless , Av1TransformSize transformSize , Av1TransformInfo transformInfo , bool useReducedTransformSet )
{
Av1TransformType transformType = Av1TransformType . DctDct ;
@ -636,8 +981,7 @@ internal ref struct Av1SymbolDecoder
}
else
{
// In intra mode, uv planes don't share the same prediction mode as y
// plane, so the tx_type should not be shared
// Chroma has its own intra mode, so its implicit transform must be derived independently of luma.
transformType = Av1SymbolContextHelper . ConvertIntraModeToTransformType ( modeInfo , Av1PlaneType . Uv ) ;
}
}
@ -651,9 +995,18 @@ internal ref struct Av1SymbolDecoder
return transformType ;
}
/// <summary>
/// Collapses a full partition distribution into the split-versus-horizontal boundary decision.
/// </summary>
/// <param name="inputs">The full partition distributions.</param>
/// <param name="blockSize">The current block size.</param>
/// <param name="context">The partition probability context.</param>
/// <returns>The binary cumulative distribution for split versus the horizontal-like partition group.</returns>
internal static Av1Distribution GetSplitOrHorizontalDistribution ( Av1Distribution [ ] inputs , Av1BlockSize blockSize , int context )
{
Av1Distribution input = inputs [ context ] ;
// At a clipped right edge, all syntax choices that advance horizontally collapse into one binary outcome.
uint p = Av1Distribution . ProbabilityTop ;
p - = GetElementProbability ( input , Av1PartitionType . Horizontal ) ;
p - = GetElementProbability ( input , Av1PartitionType . Split ) ;
@ -668,9 +1021,18 @@ internal ref struct Av1SymbolDecoder
return new ( Av1Distribution . ProbabilityTop - p ) ;
}
/// <summary>
/// Collapses a full partition distribution into the split-versus-vertical boundary decision.
/// </summary>
/// <param name="inputs">The full partition distributions.</param>
/// <param name="blockSize">The current block size.</param>
/// <param name="context">The partition probability context.</param>
/// <returns>The binary cumulative distribution for split versus the vertical-like partition group.</returns>
internal static Av1Distribution GetSplitOrVerticalDistribution ( Av1Distribution [ ] inputs , Av1BlockSize blockSize , int context )
{
Av1Distribution input = inputs [ context ] ;
// At a clipped bottom edge, all syntax choices that advance vertically collapse into one binary outcome.
uint p = Av1Distribution . ProbabilityTop ;
p - = GetElementProbability ( input , Av1PartitionType . Vertical ) ;
p - = GetElementProbability ( input , Av1PartitionType . Split ) ;
@ -685,6 +1047,12 @@ internal ref struct Av1SymbolDecoder
return new ( Av1Distribution . ProbabilityTop - p ) ;
}
/// <summary>
/// Gets one symbol's probability mass from adjacent inverse-CDF thresholds.
/// </summary>
/// <param name="probability">The inverse cumulative distribution.</param>
/// <param name="element">The partition symbol.</param>
/// <returns>The symbol's probability mass.</returns>
private static uint GetElementProbability ( Av1Distribution probability , Av1PartitionType element )
= > probability [ ( int ) element - 1 ] - probability [ ( int ) element ] ;
}
James Jackson-South
1 week ago