Implement AV1 film grain synthesis

HEIF_IMPLEMENTATION_PLAN.md

@@ -78,6 +78,7 @@ This snapshot pins or classifies the available references and failures; it does
 | `Av1WienerFilter` | AV1 sections 7.17.4 and 7.17.5 Wiener restoration filtering and coefficient derivation | libaom `av1/common/restoration.c`, `av1/common/restoration.h`, `av1/common/convolve.c`, and `av1/common/convolve.h` at `03087864cf4bea6abb0d28f95cf7843511413d8f` | Preserve the implicit center-sample contribution, separable horizontal/vertical rounding, bit-depth-dependent 16-bit intermediate range, and final 8/10/12-bit clipping. Reuse `Vector128_.MultiplyAddAdjacent` for the contiguous horizontal eight-tap product with an exact scalar fallback. Keep this scalar/SIMD oracle disabled until restoration stripe boundaries and self-guided filtering are both complete. |
 | `Av1SelfGuidedFilter` | AV1 sections 7.17.2 and 7.17.3 self-guided and box-filter processes | libaom `av1/common/restoration.c` and `av1/common/restoration.h` at `03087864cf4bea6abb0d28f95cf7843511413d8f` | Preserve the sixteen normative radius/variance parameter sets, local mean and variance normalization, alternating-row radius-two optimization, decoded projection-coefficient behavior, signed rounding, and 8/10/12-bit clipping. Use caller-owned scratch storage and a scalar oracle before considering a managed SIMD translation of libaom's architecture-specific nonlinear filter kernels. Keep this image-reconstruction stage disabled until restoration stripe boundaries are complete. |
 | `Av1LoopRestorationBoundary`, `Av1LoopRestorationDecoder`, and `Av1FrameDecoder` restoration-stage ordering | AV1 section 7.17 loop restoration, including striped boundary semantics | libaom `av1/common/restoration.c`, `av1/common/restoration.h`, `av1/common/resize.c`, and `av1/decoder/decodeframe.c` at `03087864cf4bea6abb0d28f95cf7843511413d8f` | Preserve two deblocked rows at internal 64-luma stripe boundaries before CDEF, apply the existing normative SIMD-backed super-resolution kernel to saved rows when scaled, use post-CDEF/super-resolution samples at frame edges, extend the final restoration unit up to 150 percent of nominal size, and filter from immutable plane snapshots into separate output planes. This is bounded still-image reconstruction state, not retained reference-frame, track, timing, or playback state. |
+| `Av1FilmGrainDecoder` and `Av1FilmGrainGaussianSequence` | AV1 section 7.18 film-grain synthesis | libaom `av1/decoder/grain_synthesis.c`, `av1/decoder/grain_synthesis.h`, and `aom_dsp/grain_params.h` at `03087864cf4bea6abb0d28f95cf7843511413d8f` | Preserve the normative 2,048-sample Gaussian sequence, linear-feedback shift register, luma/chroma autoregressive templates, scaling lookup interpolation, 32x32 block selection, boundary overlap, restricted-range clipping, monochrome and 4:2:0/4:2:2/4:4:4 layouts, and 8/10/12-bit arithmetic. Use allocator-owned scratch and runtime-optimized span copies. Apply grain only to the displayed still-image samples after all in-loop filters; reference-frame parameter inheritance remains sequence-playback state and is outside this codec scope. |
 | `Av1FrameInfo`, `Av1TileReader`, and `Av1BlockDecoder` transform/coefficient storage | AV1 section 5.11.39 coefficient syntax and section 7.11.2 reconstruction | libaom `av1/decoder/decodetxb.c` and `av1/decoder/decoder.h` at `03087864cf4bea6abb0d28f95cf7843511413d8f` | Preserve separate luma and chroma transform coefficients at monotonically advancing per-plane offsets within each superblock so reconstruction consumes the same transform-block order produced by tile parsing. |
 | `Av1InverseQuantizer` and `Av1InverseQuantizationLookup` | AV1 section 7.12.3 inverse quantization | libaom `aom_dsp/aom_dsp_common.h`, `av1/common/quant_common.c`, and `av1/decoder/decodetxb.c` at `03087864cf4bea6abb0d28f95cf7843511413d8f` | Select the per-segment matrix level, alias 64-pixel transform dimensions to their adjusted matrices, retain a flat level-15 matrix, and apply the five-bit inverse-matrix weight scale. The large managed lookup remains a single process-wide table. |
 | `Av1Inverse2dTransformer` and `Av1InverseTransformerFactory` | AV1 section 7.11.2 inverse transform and reconstruction | libaom `av1/common/av1_inv_txfm1d.c`, `av1/common/av1_inv_txfm2d.c`, and `av1/common/idct.c` at `03087864cf4bea6abb0d28f95cf7843511413d8f` | Scalar transform oracle for coefficient-row traversal, intermediate layout, stage ranges, clipping, and high-bit-depth sample addition. The managed 16-bit overload is also used as a parity oracle for the byte overload. |
@@ -125,10 +126,10 @@ This assessment is based on the current source after the upstream ImageSharp mer
 ### AV1 decoder
 
 - The single-still `Av1Decoder` path now parses tile state before allocating and reconstructing one independently decodable frame, and it disposes the reconstruction planes after pixel conversion. It deliberately does not retain animation/video reference frames or implement `show_existing_frame` playback state.
-- The reconstruction pipeline now records plane-relative transform geometry, preserves tile-local delta-Q and delta-LF predictors, derives segmentation and reference-adjusted filter levels, and runs the exact scalar low/high-bit-depth AV1 4-, 6-, 8-, and 14-tap deblocking kernels in normative vertical-then-horizontal order. It then applies scalar CDEF direction search, luma variance adjustment, primary and secondary constrained taps, chroma direction conversion, high-bit-depth scaling, skipped-block selection, and frame-edge sentinel handling from immutable per-plane snapshots. Active super-resolution derives the Appendix A bounded coded width and applies the exact 64-phase, 8-tap horizontal filter with aligned reconstruction-edge input, 8/10/12-bit clipping, and the existing cross-platform `Vector128_.MultiplyAddAdjacent` helper. Loop restoration now follows super-resolution, preserves the required pre-CDEF deblocked context at internal stripes, and applies decoded Wiener or self-guided units from immutable plane snapshots. Independent 8-, 10-, and 12-bit AVIF vectors exercising every active filter stage remain required before these paths have external pixel-level verification.
+- The reconstruction pipeline now records plane-relative transform geometry, preserves tile-local delta-Q and delta-LF predictors, derives segmentation and reference-adjusted filter levels, and runs the exact scalar low/high-bit-depth AV1 4-, 6-, 8-, and 14-tap deblocking kernels in normative vertical-then-horizontal order. It then applies scalar CDEF direction search, luma variance adjustment, primary and secondary constrained taps, chroma direction conversion, high-bit-depth scaling, skipped-block selection, and frame-edge sentinel handling from immutable per-plane snapshots. Active super-resolution derives the Appendix A bounded coded width and applies the exact 64-phase, 8-tap horizontal filter with aligned reconstruction-edge input, 8/10/12-bit clipping, and the existing cross-platform `Vector128_.MultiplyAddAdjacent` helper. Loop restoration follows super-resolution, preserves the required pre-CDEF deblocked context at internal stripes, and applies decoded Wiener or self-guided units from immutable plane snapshots. The visible still-image path then applies the complete self-contained film-grain parameter set after all in-loop filters. Independent 8-, 10-, and 12-bit AVIF vectors exercising every active filter and grain stage remain required before these paths have external pixel-level verification.
 - Palette mode now reads the normative luma/chroma mode and size CDFs, neighbor color caches, high-bit-depth color syntax, diagonal color-index maps, clipped-edge padding, and direct sample prediction through the existing reconstruction pipeline. The scalar implementation matches the pinned libaom source, but an independently encoded palette AVIF fixture is still required before this path is independently verified.
 - Loop-restoration unit parsing records tile-local switchable/Wiener/self-guided filter selections and coefficients in frame-owned plane grids, including super-resolution-adjusted unit corners and the corrected conditional 64x64-superblock unit-size bit. The active restoration stage implements the normative unit geometry, striped deblocked boundaries, Wiener filtering, self-guided projection, and 8/10/12-bit clipping, while reusing the existing SIMD-backed super-resolution and adjacent multiply/add primitives. Independently encoded fixtures covering every parameter set, plane layout, bit depth, and frame-edge geometry are still required. Other normative independently decodable still-image syntax paths still contain `NotImplementedException` or equivalent unsupported branches. Tile-local palette CDF adaptation is present; the remaining still-image frame-context behavior requires a separate source audit without introducing sequence playback state.
-- The frame buffer now establishes two-byte native sample storage, logical plane rows, and sample-unit block strides for 10/12-bit frames. The active intra-prediction, inverse-transform, and block-reconstruction path selects native 16-bit samples for 10/12-bit frames and has focused pipeline wiring coverage. Independently encoded high-bit-depth AVIF conformance files are still required; chroma-from-luma storage and the other normative reconstruction stages listed below remain incomplete.
+- The frame buffer now establishes two-byte native sample storage, logical plane rows, and sample-unit block strides for 10/12-bit frames. The active intra-prediction, inverse-transform, and block-reconstruction path selects native 16-bit samples for 10/12-bit frames and has focused pipeline wiring coverage. Chroma-from-luma storage, subsampling, parameter derivation, U/V sharing, and 8/10/12-bit prediction are active; independently encoded high-bit-depth and chroma-from-luma AVIF conformance files are still required.
 - `Av1YuvConverter` now consumes the signaled range, supported H.273 matrix coefficients, subsampling, and chroma sample position for 8, 10, and 12-bit output. Its high-bit-depth decode and encode paths use allocator-backed `Rgb48` rows and the existing `PixelOperations<TPixel>` conversions, avoiding the former eight-bit intermediate. Encoder conversion covers monochrome, YUV 4:2:0, 4:2:2, and 4:4:4 with libavif-compatible box averaging. Constant-luminance and chromaticity-derived matrices and ICtCp remain incomplete.
 - The inverse-transform path allocates arrays in a per-transform hot path.
 - The production prediction, transform, and nonlinear self-guided paths remain predominantly scalar. Normative super-resolution and Wiener horizontal products now reuse ImageSharp's cross-platform adjacent multiply/add SIMD helper with exact scalar fallbacks; further SIMD work must preserve these scalar reconstruction oracles.

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

@@ -66,11 +66,6 @@ internal class ObuReader
                 case ObuType.SequenceHeader:
                     this.SequenceHeader = new();
                     ReadSequenceHeader(ref reader, this.SequenceHeader);
-                    if (this.SequenceHeader.ColorConfig.BitDepth == Av1BitDepth.TwelveBit)
-                    {
-                        // TODO: Initialize 12 bit predictors
-                    }
-
                     break;
                 case ObuType.FrameHeader:
                 case ObuType.RedundantFrameHeader:

src/ImageSharp/Formats/Heif/Av1/Pipeline/Av1FrameDecoder.cs

@@ -3,6 +3,7 @@
 
 using SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 using SixLabors.ImageSharp.Formats.Heif.Av1.Pipeline.Cdef;
+using SixLabors.ImageSharp.Formats.Heif.Av1.Pipeline.FilmGrain;
 using SixLabors.ImageSharp.Formats.Heif.Av1.Pipeline.LoopFilter;
 using SixLabors.ImageSharp.Formats.Heif.Av1.Pipeline.LoopRestoration;
 using SixLabors.ImageSharp.Formats.Heif.Av1.Pipeline.Quantification;
@@ -126,8 +127,13 @@ internal class Av1FrameDecoder : IAv1FrameDecoder
             loopRestorationDecoder.DecodeFrame();
         }
 
-        // A still-image decode ends at the visible restored samples. Extending reference-frame
+        // Film grain belongs to the displayed image rather than the reference reconstruction, so it
-        // borders is sequence playback state and is deliberately outside this decoder's scope.
+        // follows every in-loop filter. This decoder owns no retained reference frames.
+        Av1FilmGrainDecoder filmGrainDecoder = new(this.sequenceHeader, this.frameHeader, this.frameBuffer);
+        filmGrainDecoder.DecodeFrame();
+
+        // Extending reference-frame borders is sequence playback state and is deliberately outside
+        // this still-image decoder's scope.
     }
 
     /// <summary>

src/ImageSharp/Formats/Heif/Av1/Pipeline/FilmGrain/Av1FilmGrainGaussianSequence.cs

@@ -0,0 +1,150 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Heif.Av1.Pipeline.FilmGrain;
+
+/// <summary>
+/// Provides the normative 2,048-sample Gaussian sequence used by AV1 film-grain synthesis.
+/// </summary>
+internal static class Av1FilmGrainGaussianSequence
+{
+    /// <summary>
+    /// The signed 12-bit Gaussian samples indexed by the film-grain pseudo-random generator.
+    /// </summary>
+    private static readonly short[] Values =
+    [
+        56, 568, -180, 172, 124, -84, 172, -64, -900, 24, 820, 224, 1248, 996, 272, -8,
+        -916, -388, -732, -104, -188, 800, 112, -652, -320, -376, 140, -252, 492, -168, 44, -788,
+        588, -584, 500, -228, 12, 680, 272, -476, 972, -100, 652, 368, 432, -196, -720, -192,
+        1000, -332, 652, -136, -552, -604, -4, 192, -220, -136, 1000, -52, 372, -96, -624, 124,
+        -24, 396, 540, -12, -104, 640, 464, 244, -208, -84, 368, -528, -740, 248, -968, -848,
+        608, 376, -60, -292, -40, -156, 252, -292, 248, 224, -280, 400, -244, 244, -60, 76,
+        -80, 212, 532, 340, 128, -36, 824, -352, -60, -264, -96, -612, 416, -704, 220, -204,
+        640, -160, 1220, -408, 900, 336, 20, -336, -96, -792, 304, 48, -28, -1232, -1172, -448,
+        104, -292, -520, 244, 60, -948, 0, -708, 268, 108, 356, -548, 488, -344, -136, 488,
+        -196, -224, 656, -236, -1128, 60, 4, 140, 276, -676, -376, 168, -108, 464, 8, 564,
+        64, 240, 308, -300, -400, -456, -136, 56, 120, -408, -116, 436, 504, -232, 328, 844,
+        -164, -84, 784, -168, 232, -224, 348, -376, 128, 568, 96, -1244, -288, 276, 848, 832,
+        -360, 656, 464, -384, -332, -356, 728, -388, 160, -192, 468, 296, 224, 140, -776, -100,
+        280, 4, 196, 44, -36, -648, 932, 16, 1428, 28, 528, 808, 772, 20, 268, 88,
+        -332, -284, 124, -384, -448, 208, -228, -1044, -328, 660, 380, -148, -300, 588, 240, 540,
+        28, 136, -88, -436, 256, 296, -1000, 1400, 0, -48, 1056, -136, 264, -528, -1108, 632,
+        -484, -592, -344, 796, 124, -668, -768, 388, 1296, -232, -188, -200, -288, -4, 308, 100,
+        -168, 256, -500, 204, -508, 648, -136, 372, -272, -120, -1004, -552, -548, -384, 548, -296,
+        428, -108, -8, -912, -324, -224, -88, -112, -220, -100, 996, -796, 548, 360, -216, 180,
+        428, -200, -212, 148, 96, 148, 284, 216, -412, -320, 120, -300, -384, -604, -572, -332,
+        -8, -180, -176, 696, 116, -88, 628, 76, 44, -516, 240, -208, -40, 100, -592, 344,
+        -308, -452, -228, 20, 916, -1752, -136, -340, -804, 140, 40, 512, 340, 248, 184, -492,
+        896, -156, 932, -628, 328, -688, -448, -616, -752, -100, 560, -1020, 180, -800, -64, 76,
+        576, 1068, 396, 660, 552, -108, -28, 320, -628, 312, -92, -92, -472, 268, 16, 560,
+        516, -672, -52, 492, -100, 260, 384, 284, 292, 304, -148, 88, -152, 1012, 1064, -228,
+        164, -376, -684, 592, -392, 156, 196, -524, -64, -884, 160, -176, 636, 648, 404, -396,
+        -436, 864, 424, -728, 988, -604, 904, -592, 296, -224, 536, -176, -920, 436, -48, 1176,
+        -884, 416, -776, -824, -884, 524, -548, -564, -68, -164, -96, 692, 364, -692, -1012, -68,
+        260, -480, 876, -1116, 452, -332, -352, 892, -1088, 1220, -676, 12, -292, 244, 496, 372,
+        -32, 280, 200, 112, -440, -96, 24, -644, -184, 56, -432, 224, -980, 272, -260, 144,
+        -436, 420, 356, 364, -528, 76, 172, -744, -368, 404, -752, -416, 684, -688, 72, 540,
+        416, 92, 444, 480, -72, -1416, 164, -1172, -68, 24, 424, 264, 1040, 128, -912, -524,
+        -356, 64, 876, -12, 4, -88, 532, 272, -524, 320, 276, -508, 940, 24, -400, -120,
+        756, 60, 236, -412, 100, 376, -484, 400, -100, -740, -108, -260, 328, -268, 224, -200,
+        -416, 184, -604, -564, -20, 296, 60, 892, -888, 60, 164, 68, -760, 216, -296, 904,
+        -336, -28, 404, -356, -568, -208, -1480, -512, 296, 328, -360, -164, -1560, -776, 1156, -428,
+        164, -504, -112, 120, -216, -148, -264, 308, 32, 64, -72, 72, 116, 176, -64, -272,
+        460, -536, -784, -280, 348, 108, -752, -132, 524, -540, -776, 116, -296, -1196, -288, -560,
+        1040, -472, 116, -848, -1116, 116, 636, 696, 284, -176, 1016, 204, -864, -648, -248, 356,
+        972, -584, -204, 264, 880, 528, -24, -184, 116, 448, -144, 828, 524, 212, -212, 52,
+        12, 200, 268, -488, -404, -880, 824, -672, -40, 908, -248, 500, 716, -576, 492, -576,
+        16, 720, -108, 384, 124, 344, 280, 576, -500, 252, 104, -308, 196, -188, -8, 1268,
+        296, 1032, -1196, 436, 316, 372, -432, -200, -660, 704, -224, 596, -132, 268, 32, -452,
+        884, 104, -1008, 424, -1348, -280, 4, -1168, 368, 476, 696, 300, -8, 24, 180, -592,
+        -196, 388, 304, 500, 724, -160, 244, -84, 272, -256, -420, 320, 208, -144, -156, 156,
+        364, 452, 28, 540, 316, 220, -644, -248, 464, 72, 360, 32, -388, 496, -680, -48,
+        208, -116, -408, 60, -604, -392, 548, -840, 784, -460, 656, -544, -388, -264, 908, -800,
+        -628, -612, -568, 572, -220, 164, 288, -16, -308, 308, -112, -636, -760, 280, -668, 432,
+        364, 240, -196, 604, 340, 384, 196, 592, -44, -500, 432, -580, -132, 636, -76, 392,
+        4, -412, 540, 508, 328, -356, -36, 16, -220, -64, -248, -60, 24, -192, 368, 1040,
+        92, -24, -1044, -32, 40, 104, 148, 192, -136, -520, 56, -816, -224, 732, 392, 356,
+        212, -80, -424, -1008, -324, 588, -1496, 576, 460, -816, -848, 56, -580, -92, -1372, -112,
+        -496, 200, 364, 52, -140, 48, -48, -60, 84, 72, 40, 132, -356, -268, -104, -284,
+        -404, 732, -520, 164, -304, -540, 120, 328, -76, -460, 756, 388, 588, 236, -436, -72,
+        -176, -404, -316, -148, 716, -604, 404, -72, -88, -888, -68, 944, 88, -220, -344, 960,
+        472, 460, -232, 704, 120, 832, -228, 692, -508, 132, -476, 844, -748, -364, -44, 1116,
+        -1104, -1056, 76, 428, 552, -692, 60, 356, 96, -384, -188, -612, -576, 736, 508, 892,
+        352, -1132, 504, -24, -352, 324, 332, -600, -312, 292, 508, -144, -8, 484, 48, 284,
+        -260, -240, 256, -100, -292, -204, -44, 472, -204, 908, -188, -1000, -256, 92, 1164, -392,
+        564, 356, 652, -28, -884, 256, 484, -192, 760, -176, 376, -524, -452, -436, 860, -736,
+        212, 124, 504, -476, 468, 76, -472, 552, -692, -944, -620, 740, -240, 400, 132, 20,
+        192, -196, 264, -668, -1012, -60, 296, -316, -828, 76, -156, 284, -768, -448, -832, 148,
+        248, 652, 616, 1236, 288, -328, -400, -124, 588, 220, 520, -696, 1032, 768, -740, -92,
+        -272, 296, 448, -464, 412, -200, 392, 440, -200, 264, -152, -260, 320, 1032, 216, 320,
+        -8, -64, 156, -1016, 1084, 1172, 536, 484, -432, 132, 372, -52, -256, 84, 116, -352,
+        48, 116, 304, -384, 412, 924, -300, 528, 628, 180, 648, 44, -980, -220, 1320, 48,
+        332, 748, 524, -268, -720, 540, -276, 564, -344, -208, -196, 436, 896, 88, -392, 132,
+        80, -964, -288, 568, 56, -48, -456, 888, 8, 552, -156, -292, 948, 288, 128, -716,
+        -292, 1192, -152, 876, 352, -600, -260, -812, -468, -28, -120, -32, -44, 1284, 496, 192,
+        464, 312, -76, -516, -380, -456, -1012, -48, 308, -156, 36, 492, -156, -808, 188, 1652,
+        68, -120, -116, 316, 160, -140, 352, 808, -416, 592, 316, -480, 56, 528, -204, -568,
+        372, -232, 752, -344, 744, -4, 324, -416, -600, 768, 268, -248, -88, -132, -420, -432,
+        80, -288, 404, -316, -1216, -588, 520, -108, 92, -320, 368, -480, -216, -92, 1688, -300,
+        180, 1020, -176, 820, -68, -228, -260, 436, -904, 20, 40, -508, 440, -736, 312, 332,
+        204, 760, -372, 728, 96, -20, -632, -520, -560, 336, 1076, -64, -532, 776, 584, 192,
+        396, -728, -520, 276, -188, 80, -52, -612, -252, -48, 648, 212, -688, 228, -52, -260,
+        428, -412, -272, -404, 180, 816, -796, 48, 152, 484, -88, -216, 988, 696, 188, -528,
+        648, -116, -180, 316, 476, 12, -564, 96, 476, -252, -364, -376, -392, 556, -256, -576,
+        260, -352, 120, -16, -136, -260, -492, 72, 556, 660, 580, 616, 772, 436, 424, -32,
+        -324, -1268, 416, -324, -80, 920, 160, 228, 724, 32, -516, 64, 384, 68, -128, 136,
+        240, 248, -204, -68, 252, -932, -120, -480, -628, -84, 192, 852, -404, -288, -132, 204,
+        100, 168, -68, -196, -868, 460, 1080, 380, -80, 244, 0, 484, -888, 64, 184, 352,
+        600, 460, 164, 604, -196, 320, -64, 588, -184, 228, 12, 372, 48, -848, -344, 224,
+        208, -200, 484, 128, -20, 272, -468, -840, 384, 256, -720, -520, -464, -580, 112, -120,
+        644, -356, -208, -608, -528, 704, 560, -424, 392, 828, 40, 84, 200, -152, 0, -144,
+        584, 280, -120, 80, -556, -972, -196, -472, 724, 80, 168, -32, 88, 160, -688, 0,
+        160, 356, 372, -776, 740, -128, 676, -248, -480, 4, -364, 96, 544, 232, -1032, 956,
+        236, 356, 20, -40, 300, 24, -676, -596, 132, 1120, -104, 532, -1096, 568, 648, 444,
+        508, 380, 188, -376, -604, 1488, 424, 24, 756, -220, -192, 716, 120, 920, 688, 168,
+        44, -460, 568, 284, 1144, 1160, 600, 424, 888, 656, -356, -320, 220, 316, -176, -724,
+        -188, -816, -628, -348, -228, -380, 1012, -452, -660, 736, 928, 404, -696, -72, -268, -892,
+        128, 184, -344, -780, 360, 336, 400, 344, 428, 548, -112, 136, -228, -216, -820, -516,
+        340, 92, -136, 116, -300, 376, -244, 100, -316, -520, -284, -12, 824, 164, -548, -180,
+        -128, 116, -924, -828, 268, -368, -580, 620, 192, 160, 0, -1676, 1068, 424, -56, -360,
+        468, -156, 720, 288, -528, 556, -364, 548, -148, 504, 316, 152, -648, -620, -684, -24,
+        -376, -384, -108, -920, -1032, 768, 180, -264, -508, -1268, -260, -60, 300, -240, 988, 724,
+        -376, -576, -212, -736, 556, 192, 1092, -620, -880, 376, -56, -4, -216, -32, 836, 268,
+        396, 1332, 864, -600, 100, 56, -412, -92, 356, 180, 884, -468, -436, 292, -388, -804,
+        -704, -840, 368, -348, 140, -724, 1536, 940, 372, 112, -372, 436, -480, 1136, 296, -32,
+        -228, 132, -48, -220, 868, -1016, -60, -1044, -464, 328, 916, 244, 12, -736, -296, 360,
+        468, -376, -108, -92, 788, 368, -56, 544, 400, -672, -420, 728, 16, 320, 44, -284,
+        -380, -796, 488, 132, 204, -596, -372, 88, -152, -908, -636, -572, -624, -116, -692, -200,
+        -56, 276, -88, 484, -324, 948, 864, 1000, -456, -184, -276, 292, -296, 156, 676, 320,
+        160, 908, -84, -1236, -288, -116, 260, -372, -644, 732, -756, -96, 84, 344, -520, 348,
+        -688, 240, -84, 216, -1044, -136, -676, -396, -1500, 960, -40, 176, 168, 1516, 420, -504,
+        -344, -364, -360, 1216, -940, -380, -212, 252, -660, -708, 484, -444, -152, 928, -120, 1112,
+        476, -260, 560, -148, -344, 108, -196, 228, -288, 504, 560, -328, -88, 288, -1008, 460,
+        -228, 468, -836, -196, 76, 388, 232, 412, -1168, -716, -644, 756, -172, -356, -504, 116,
+        432, 528, 48, 476, -168, -608, 448, 160, -532, -272, 28, -676, -12, 828, 980, 456,
+        520, 104, -104, 256, -344, -4, -28, -368, -52, -524, -572, -556, -200, 768, 1124, -208,
+        -512, 176, 232, 248, -148, -888, 604, -600, -304, 804, -156, -212, 488, -192, -804, -256,
+        368, -360, -916, -328, 228, -240, -448, -472, 856, -556, -364, 572, -12, -156, -368, -340,
+        432, 252, -752, -152, 288, 268, -580, -848, -592, 108, -76, 244, 312, -716, 592, -80,
+        436, 360, 4, -248, 160, 516, 584, 732, 44, -468, -280, -292, -156, -588, 28, 308,
+        912, 24, 124, 156, 180, -252, 944, -924, -772, -520, -428, -624, 300, -212, -1144, 32,
+        -724, 800, -1128, -212, -1288, -848, 180, -416, 440, 192, -576, -792, -76, -1080, 80, -532,
+        -352, -132, 380, -820, 148, 1112, 128, 164, 456, 700, -924, 144, -668, -384, 648, -832,
+        508, 552, -52, -100, -656, 208, -568, 748, -88, 680, 232, 300, 192, -408, -1012, -152,
+        -252, -268, 272, -876, -664, -648, -332, -136, 16, 12, 1152, -28, 332, -536, 320, -672,
+        -460, -316, 532, -260, 228, -40, 1052, -816, 180, 88, -496, -556, -672, -368, 428, 92,
+        356, 404, -408, 252, 196, -176, -556, 792, 268, 32, 372, 40, 96, -332, 328, 120,
+        372, -900, -40, 472, -264, -592, 952, 128, 656, 112, 664, -232, 420, 4, -344, -464,
+        556, 244, -416, -32, 252, 0, -412, 188, -696, 508, -476, 324, -1096, 656, -312, 560,
+        264, -136, 304, 160, -64, -580, 248, 336, -720, 560, -348, -288, -276, -196, -500, 852,
+        -544, -236, -1128, -992, -776, 116, 56, 52, 860, 884, 212, -12, 168, 1020, 512, -552,
+        924, -148, 716, 188, 164, -340, -520, -184, 880, -152, -680, -208, -1156, -300, -528, -472,
+        364, 100, -744, -1056, -32, 540, 280, 144, -676, -32, -232, -280, -224, 96, 568, -76,
+        172, 148, 148, 104, 32, -296, -32, 788, -80, 32, -16, 280, 288, 944, 428, -484,
+    ];
+
+    /// <summary>
+    /// Gets the Gaussian samples in their normative index order.
+    /// </summary>
+    public static ReadOnlySpan<short> Samples => Values;
+}

src/ImageSharp/Formats/Heif/Av1/Prediction/Av1PredictionDecoder.cs

@@ -361,8 +361,6 @@ internal class Av1PredictionDecoder
         Av1BitDepth bitDepth)
         where T : unmanaged, IBinaryInteger<T>
     {
-        // TODO:are_parameters_computed variable for CFL so that cal part for V plane we can skip,
-        // once we compute for U plane, this parameter is block level parameter.
         ObuColorConfig cc = this.sequenceHeader.ColorConfig;
         int subX = plane != Av1Plane.Y ? cc.SubSamplingX ? 1 : 0 : 0;
         int subY = plane != Av1Plane.Y ? cc.SubSamplingY ? 1 : 0 : 0;