Correct HEVC intra edge filtering

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

@@ -17,8 +17,9 @@ internal sealed partial class HevcPictureDecoder
     /// <param name="log2Size">The base-two logarithm of the square prediction-block side.</param>
     /// <param name="regionId">The current independent-slice and tile prediction region.</param>
     /// <param name="colorPlaneIndex">The selected separate-color plane, or zero for combined coding.</param>
+    /// <param name="transquantBypass">Whether the governing coding unit bypasses inverse quantization and transform.</param>
     /// <returns>The packed predicted samples.</returns>
-    private Span<ushort> PredictComponentBlock(HevcPlane plane, int x, int y, int log2Size, int regionId, int colorPlaneIndex)
+    private Span<ushort> PredictComponentBlock(HevcPlane plane, int x, int y, int log2Size, int regionId, int colorPlaneIndex, bool transquantBypass)
     {
         int size = 1 << log2Size;
         int sampleCount = size * size;
@@ -69,6 +70,14 @@ internal sealed partial class HevcPictureDecoder
             mode = HevcIntraPredictionMode.RemapChroma422(mode);
         }
 
+        // H.265 8.4.4.2.3 and 8.4.4.2.6 restrict prediction-edge filtering to luma blocks no larger than 16 samples.
+        // Implicit RDPCM bypasses that filtering for the lossless horizontal and vertical prediction modes.
+        bool filterPredictionEdges = useLumaSyntax
+            && size <= 16
+            && !(transquantBypass
+                && this.sequenceParameterSet.ImplicitResidualDpcmEnabled
+                && (mode == HevcIntraPredictionMode.Horizontal || mode == HevcIntraPredictionMode.Vertical));
+
         bool filterReferences = HevcIntraPredictor.ShouldFilterReferenceSamples(
             useLumaSyntax ? HevcPlane.Y : plane,
             mode,
@@ -101,7 +110,7 @@ internal sealed partial class HevcPictureDecoder
             log2Size,
             mode,
             this.Picture.GetBitDepth(plane),
-            useLumaSyntax,
+            filterPredictionEdges,
             operationScratch);
 
         return prediction;

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

@@ -369,7 +369,7 @@ internal sealed partial class HevcPictureDecoder
         Span<int> dequantized = integerScratch.Slice(MaximumTransformSampleCount, MaximumTransformSampleCount);
         Span<int> residual = integerScratch.Slice(MaximumTransformSampleCount * 2, MaximumTransformSampleCount);
         Span<int> transformScratch = integerScratch.Slice(MaximumTransformSampleCount * 4, MaximumTransformSampleCount * 2);
-        Span<ushort> prediction = this.PredictComponentBlock(plane, x, y, log2Size, regionId, colorPlaneIndex);
+        Span<ushort> prediction = this.PredictComponentBlock(plane, x, y, log2Size, regionId, colorPlaneIndex, transquantBypass);
         residual[..sampleCount].Clear();
         bool useLumaSyntax = this.sequenceParameterSet.SeparateColorPlaneFlag;
         HevcPlane codingPlane = useLumaSyntax ? HevcPlane.Y : plane;

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

@@ -21,6 +21,7 @@ public class HevcPictureDecoderTests
     [InlineData(TestImages.Heif.Image1TileHvcConfiguration, TestImages.Heif.Image1Tile1Payload, TestImages.Heif.Image1Tile1ReferenceYuv)]
     [InlineData(TestImages.Heif.Image1TileHvcConfiguration, TestImages.Heif.Image1Tile2Payload, TestImages.Heif.Image1Tile2ReferenceYuv)]
     [InlineData(TestImages.Heif.Image2TileHvcConfiguration, TestImages.Heif.Image2Tile1Payload, TestImages.Heif.Image2Tile1ReferenceYuv)]
+    [InlineData(TestImages.Heif.Image2TileHvcConfiguration, TestImages.Heif.Image2Tile7Payload, TestImages.Heif.Image2Tile7ReferenceYuv)]
     [InlineData(TestImages.Heif.DwsampleTileHvcConfiguration, TestImages.Heif.DwsampleTilePayload, TestImages.Heif.DwsampleTileReferenceYuv)]
     public void DecodeRealHeicTileMatchesHmReference(string configurationPath, string itemPath, string referencePath)
     {

tests/ImageSharp.Tests/TestImages.cs

@@ -1289,6 +1289,8 @@ public static class TestImages
         public const string Image2TileHvcConfiguration = "Heif/Hevc/image2-tile.hvcc";
         public const string Image2Tile1Payload = "Heif/Hevc/image2-tile1.hvc1";
         public const string Image2Tile1ReferenceYuv = "Heif/Hevc/image2-tile1-hm.yuv";
+        public const string Image2Tile7Payload = "Heif/Hevc/image2-tile7.hvc1";
+        public const string Image2Tile7ReferenceYuv = "Heif/Hevc/image2-tile7-hm.yuv";
         public const string DwsampleTileHvcConfiguration = "Heif/Hevc/dwsample-tile.hvcc";
         public const string DwsampleTilePayload = "Heif/Hevc/dwsample-tile.hvc1";
         public const string DwsampleTileReferenceYuv = "Heif/Hevc/dwsample-tile-hm.yuv";

tests/Images/Input/Heif/Hevc/image2-tile7-hm.yuv

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:d85526927c19fd642b7173215767d2e822e4d0eda58eaae3bb5e3a498659ea4f
+size 393216

tests/Images/Input/Heif/Hevc/image2-tile7.hvc1

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6bd5ebc70cea2c8359a3afdd81eed0cdb9e86616516a7b974a7f8017139bb939
+size 7945