Fix frame buffer extents

src/ImageSharp/Formats/Heif/Av1/Av1FrameBuffer.cs

@@ -49,15 +49,15 @@ internal class Av1FrameBuffer<T> : IDisposable
         {
             case Av1ColorFormat.Yuv420:
                 strideChroma = (strideY + 1) >> 1;
-                heightChroma = (this.Height + 1) >> 1;
+                heightChroma = (heightY + 1) >> 1;
                 break;
             case Av1ColorFormat.Yuv422:
                 strideChroma = (strideY + 1) >> 1;
-                heightChroma = this.Height;
+                heightChroma = heightY;
                 break;
             case Av1ColorFormat.Yuv444:
                 strideChroma = strideY;
-                heightChroma = this.Height;
+                heightChroma = heightY;
                 break;
         }
 

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

@@ -24,6 +24,9 @@ internal class Av1PredictionDecoder
         this.is16BitPipeline = is16BitPipeline;
     }
 
+    /// <summary>
+    /// SVT: svt_av1_predict_intra
+    /// </summary>
     public void Decode(
         Av1PartitionInfo partitionInfo,
         Av1Plane plane,
@@ -37,8 +40,11 @@ internal class Av1PredictionDecoder
     {
         int bytesPerPixel = (bitDepth == Av1BitDepth.EightBit && !this.is16BitPipeline) ? 2 : 1;
         int stride = pixelStride * bytesPerPixel;
-        Span<byte> topNeighbor = pixelBuffer.Slice(-stride);
-        Span<byte> leftNeighbor = pixelBuffer.Slice(-1);
+
+        // Deviation from SVT: Buffer starts at PREVIOUS row.
+        Span<byte> topNeighbor = pixelBuffer;
+        Span<byte> leftNeighbor = pixelBuffer[(stride - 1)..];
+        Span<byte> startOfPixels = pixelBuffer[stride..];
 
         bool is16BitPipeline = this.is16BitPipeline;
         Av1PredictionMode mode = (plane == Av1Plane.Y) ? partitionInfo.ModeInfo.YMode : partitionInfo.ModeInfo.UvMode;
@@ -50,7 +56,7 @@ internal class Av1PredictionDecoder
                 plane,
                 transformSize,
                 tileInfo,
-                pixelBuffer,
+                startOfPixels,
                 stride,
                 topNeighbor,
                 leftNeighbor,
@@ -63,7 +69,7 @@ internal class Av1PredictionDecoder
             this.PredictChromaFromLumaBlock(
                 partitionInfo,
                 partitionInfo.ChromaFromLumaContext,
-                ref pixelBuffer,
+                startOfPixels,
                 stride,
                 transformSize,
                 plane);
@@ -76,7 +82,7 @@ internal class Av1PredictionDecoder
             plane,
             transformSize,
             tileInfo,
-            pixelBuffer,
+            startOfPixels,
             stride,
             topNeighbor,
             leftNeighbor,
@@ -87,7 +93,7 @@ internal class Av1PredictionDecoder
             bitDepth);
     }
 
-    private void PredictChromaFromLumaBlock(Av1PartitionInfo partitionInfo, Av1ChromaFromLumaContext? chromaFromLumaContext, ref Span<byte> pixelBuffer, int stride, Av1TransformSize transformSize, Av1Plane plane)
+    private void PredictChromaFromLumaBlock(Av1PartitionInfo partitionInfo, Av1ChromaFromLumaContext? chromaFromLumaContext, Span<byte> pixelBuffer, int stride, Av1TransformSize transformSize, Av1Plane plane)
     {
         Av1BlockModeInfo modeInfo = partitionInfo.ModeInfo;
         bool isChromaFromLumaAllowedFlag = IsChromaFromLumaAllowedWithFrameHeader(partitionInfo, this.sequenceHeader.ColorConfig, this.frameHeader);

src/ImageSharp/Formats/Heif/Av1/Transform/Av1BlockDecoder.cs

@@ -146,7 +146,6 @@ internal class Av1BlockDecoder
                 }
 
                 // if (!inter_block)
-                if (true)
                 {
                     // SVT: svt_av1_predict_intra
                     predictionDecoder.Decode(
@@ -226,25 +225,29 @@ internal class Av1BlockDecoder
     {
         int blockOffset;
 
-        if (plane == 0)
+        switch (plane)
         {
-            blockOffset = ((frameBuffer.OriginY + blockRowInPixels) * frameBuffer.BufferY!.Width) +
-                (frameBuffer.OriginX + blockColumnInPixels);
-            reconstructionStride = frameBuffer.BufferY!.Width;
-        }
-        else if (plane == 1)
-        {
-            blockOffset = (((frameBuffer.OriginY >> subY) + blockRowInPixels) * frameBuffer.BufferCb!.Width) +
-                ((frameBuffer.OriginX >> subX) + blockColumnInPixels);
-            reconstructionStride = frameBuffer.BufferCb!.Width;
-        }
-        else
-        {
-            blockOffset = (((frameBuffer.OriginY >> subY) + blockRowInPixels) * frameBuffer.BufferCr!.Width) +
-                ((frameBuffer.OriginX >> subX) + blockColumnInPixels);
-            reconstructionStride = frameBuffer.BufferCr!.Width;
+            case 0:
+                reconstructionStride = frameBuffer.BufferY!.Width;
+                blockOffset = ((frameBuffer.OriginY + blockRowInPixels) * reconstructionStride) +
+                    (frameBuffer.OriginX + blockColumnInPixels);
+                break;
+            case 1:
+                reconstructionStride = frameBuffer.BufferCb!.Width;
+                blockOffset = (((frameBuffer.OriginY >> subY) + blockRowInPixels) * reconstructionStride) +
+                    ((frameBuffer.OriginX >> subX) + blockColumnInPixels);
+                break;
+            default:
+                reconstructionStride = frameBuffer.BufferCr!.Width;
+                blockOffset = (((frameBuffer.OriginY >> subY) + blockRowInPixels) * reconstructionStride) +
+                    ((frameBuffer.OriginX >> subX) + blockColumnInPixels);
+                break;
         }
 
+        // Deviation from SVT, return PREVIOUS row in Block Reconstruction Buffer.
+        blockOffset -= reconstructionStride;
+        Guard.MustBeGreaterThanOrEqualTo(blockOffset, 0, nameof(blockOffset));
+
         if (frameBuffer.BitDepth != Av1BitDepth.EightBit || frameBuffer.Is16BitPipeline)
         {
             // 16bit pipeline