diff --git a/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1ParseAboveNeighbor4x4Context.cs b/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1ParseAboveNeighbor4x4Context.cs
index 1810bf6fc4..574735528d 100644
--- a/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1ParseAboveNeighbor4x4Context.cs
+++ b/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1ParseAboveNeighbor4x4Context.cs
@@ -81,13 +81,10 @@ internal class Av1ParseAboveNeighbor4x4Context
         int n4w = blockSize.Get4x4WideCount();
         if (skip)
         {
-            transformWidth = n4w * (1 << Av1Constants.ModeInfoSizeLog2);
+            transformWidth = n4w << Av1Constants.ModeInfoSizeLog2;
         }
 
-        for (int i = 0; i < n4w; i++)
-        {
-            this.aboveTransformWidth[startIndex + i] = transformWidth;
-        }
+        Array.Fill(this.aboveTransformWidth, transformWidth, startIndex, n4w);
     }
 
     internal void ClearContext(int plane, int offset, int length)
diff --git a/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1ParseLeftNeighbor4x4Context.cs b/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1ParseLeftNeighbor4x4Context.cs
index 8743ee329e..f505774746 100644
--- a/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1ParseLeftNeighbor4x4Context.cs
+++ b/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1ParseLeftNeighbor4x4Context.cs
@@ -80,13 +80,11 @@ internal class Av1ParseLeftNeighbor4x4Context
         int n4h = blockSize.Get4x4HighCount();
         if (skip)
         {
-            transformHeight = n4h * (1 << Av1Constants.ModeInfoSizeLog2);
+            transformHeight = n4h << Av1Constants.ModeInfoSizeLog2;
         }
 
-        for (int i = 0; i < n4h; i++)
-        {
-            this.leftTransformHeight[startIndex + i] = transformHeight;
-        }
+        DebugGuard.MustBeLessThanOrEqualTo(startIndex + n4h, this.leftTransformHeight.Length, nameof(startIndex));
+        Array.Fill(this.leftTransformHeight, transformHeight, startIndex, n4h);
     }
 
     internal void ClearContext(int plane, int offset, int length)
diff --git a/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1PartitionInfo.cs b/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1PartitionInfo.cs
index 1a73c5eefc..99994f2d94 100644
--- a/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1PartitionInfo.cs
+++ b/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1PartitionInfo.cs
@@ -84,10 +84,11 @@ internal class Av1PartitionInfo
         this.AvailableLeft = this.ColumnIndex > tileInfo.ModeInfoColumnStart;
         this.AvailableAboveForChroma = this.AvailableAbove;
         this.AvailableLeftForChroma = this.AvailableLeft;
-        this.modeBlockToLeftEdge = -(this.ColumnIndex << Av1Constants.ModeInfoSizeLog2) << 3;
-        this.modeBlockToRightEdge = ((frameInfo.ModeInfoColumnCount - bw4 - this.ColumnIndex) << Av1Constants.ModeInfoSizeLog2) << 3;
-        this.modeBlockToTopEdge = -(this.RowIndex << Av1Constants.ModeInfoSizeLog2) << 3;
-        this.modeBlockToBottomEdge = ((frameInfo.ModeInfoRowCount - bh4 - this.RowIndex) << Av1Constants.ModeInfoSizeLog2) << 3;
+        int shift = Av1Constants.ModeInfoSizeLog2 + 3;
+        this.modeBlockToLeftEdge = -this.ColumnIndex << shift;
+        this.modeBlockToRightEdge = (frameInfo.ModeInfoColumnCount - bw4 - this.ColumnIndex) << shift;
+        this.modeBlockToTopEdge = -this.RowIndex << shift;
+        this.modeBlockToBottomEdge = (frameInfo.ModeInfoRowCount - bh4 - this.RowIndex) << shift;
     }
 
     public int GetMaxBlockWide(Av1BlockSize blockSize, bool subX)
diff --git a/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1TileDecoder.cs b/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1TileDecoder.cs
index eeffbac337..285e5d13d9 100644
--- a/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1TileDecoder.cs
+++ b/src/ImageSharp/Formats/Heif/Av1/Tiling/Av1TileDecoder.cs
@@ -1285,17 +1285,16 @@ internal class Av1TileDecoder : IAv1TileDecoder
         int block4x4Height = blockSize.Get4x4HighCount();
 
         // First condition in spec is for INTER frames, implemented only the INTRA condition.
-        bool allowSelect = !partitionInfo.ModeInfo.Skip || true;
-        Av1TransformSize transformSize = this.ReadTransformSize(ref reader, partitionInfo, superblockInfo, tileInfo, allowSelect);
+        Av1TransformSize transformSize = this.ReadTransformSize(ref reader, partitionInfo, superblockInfo, tileInfo, true);
         this.aboveNeighborContext.UpdateTransformation(modeInfoLocation, tileInfo, transformSize, blockSize, false);
         this.leftNeighborContext.UpdateTransformation(modeInfoLocation, superblockInfo, transformSize, blockSize, false);
-        this.UpdateTransformInfo(partitionInfo, blockSize, transformSize);
+        this.UpdateTransformInfo(partitionInfo, superblockInfo, blockSize, transformSize);
     }
 
-    private unsafe void UpdateTransformInfo(Av1PartitionInfo partitionInfo, Av1BlockSize blockSize, Av1TransformSize transformSize)
+    private unsafe void UpdateTransformInfo(Av1PartitionInfo partitionInfo, Av1SuperblockInfo superblockInfo, Av1BlockSize blockSize, Av1TransformSize transformSize)
     {
-        int transformInfoYIndex = partitionInfo.ModeInfo.FirstTransformLocation[(int)Av1PlaneType.Y];
-        int transformInfoUvIndex = partitionInfo.ModeInfo.FirstTransformLocation[(int)Av1PlaneType.Uv];
+        int transformInfoYIndex = superblockInfo.TransformInfoIndexY + partitionInfo.ModeInfo.FirstTransformLocation[(int)Av1PlaneType.Y];
+        int transformInfoUvIndex = superblockInfo.TransformInfoIndexUv + partitionInfo.ModeInfo.FirstTransformLocation[(int)Av1PlaneType.Uv];
         Av1TransformInfo lumaTransformInfo = this.FrameBuffer.GetTransformY(transformInfoYIndex);
         Av1TransformInfo chromaTransformInfo = this.FrameBuffer.GetTransformUv(transformInfoUvIndex);
         int totalLumaTusCount = 0;
@@ -1324,8 +1323,8 @@ internal class Av1TileDecoder : IAv1TileDecoder
                 int stepColumn = transformSize.Get4x4WideCount();
                 int stepRow = transformSize.Get4x4HighCount();
 
-                int unitHeight = Av1Math.Round2(Math.Min(height + idy, maxBlockHigh), 0);
-                int unitWidth = Av1Math.Round2(Math.Min(width + idx, maxBlockWide), 0);
+                int unitHeight = Av1Math.RoundPowerOf2(Math.Min(height + idy, maxBlockHigh), 0);
+                int unitWidth = Av1Math.RoundPowerOf2(Math.Min(width + idx, maxBlockWide), 0);
                 for (int blockRow = idy; blockRow < unitHeight; blockRow += stepRow)
                 {
                     for (int blockColumn = idx; blockColumn < unitWidth; blockColumn += stepColumn)
@@ -1349,8 +1348,8 @@ internal class Av1TileDecoder : IAv1TileDecoder
                 stepColumn = transformSizeUv.Get4x4WideCount();
                 stepRow = transformSizeUv.Get4x4HighCount();
 
-                unitHeight = Av1Math.Round2(Math.Min(height + idx, maxBlockHigh), subY ? 1 : 0);
-                unitWidth = Av1Math.Round2(Math.Min(width + idx, maxBlockWide), subX ? 1 : 0);
+                unitHeight = Av1Math.RoundPowerOf2(Math.Min(height + idx, maxBlockHigh), subY ? 1 : 0);
+                unitWidth = Av1Math.RoundPowerOf2(Math.Min(width + idx, maxBlockWide), subX ? 1 : 0);
                 for (int blockRow = idy; blockRow < unitHeight; blockRow += stepRow)
                 {
                     for (int blockColumn = idx; blockColumn < unitWidth; blockColumn += stepColumn)
@@ -1382,7 +1381,7 @@ internal class Av1TileDecoder : IAv1TileDecoder
         partitionInfo.ModeInfo.TusCount[(int)Av1PlaneType.Uv] = totalChromaTusCount;
 
         this.firstTransformOffset[(int)Av1PlaneType.Y] += totalLumaTusCount;
-        this.firstTransformOffset[(int)Av1PlaneType.Uv] += totalChromaTusCount;
+        this.firstTransformOffset[(int)Av1PlaneType.Uv] += totalChromaTusCount << 1;
     }
 
     /// <summary>