diff --git a/src/ImageSharp/Formats/Jxl/Ac/JxlAcStrategyType.cs b/src/ImageSharp/Formats/Jxl/Ac/JxlAcStrategyType.cs
new file mode 100644
index 0000000000..3412d10f46
--- /dev/null
+++ b/src/ImageSharp/Formats/Jxl/Ac/JxlAcStrategyType.cs
@@ -0,0 +1,67 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Ac;
+
+internal enum JxlAcStrategyType : ushort
+{
+    // Regular block size DCT
+    DCT = 0,
+
+    // Encode pixels without transforming
+    IDENTITY = 1,
+
+    // Use 2-by-2 DCT
+    DCT2X2 = 2,
+
+    // Use 4-by-4 DCT
+    DCT4X4 = 3,
+
+    // Use 16-by-16 DCT
+    DCT16X16 = 4,
+
+    // Use 32-by-32 DCT
+    DCT32X32 = 5,
+
+    // Use 16-by-8 DCT
+    DCT16X8 = 6,
+
+    // Use 8-by-16 DCT
+    DCT8X16 = 7,
+
+    // Use 32-by-8 DCT
+    DCT32X8 = 8,
+
+    // Use 8-by-32 DCT
+    DCT8X32 = 9,
+
+    // Use 32-by-16 DCT
+    DCT32X16 = 10,
+
+    // Use 16-by-32 DCT
+    DCT16X32 = 11,
+
+    // 4x8 and 8x4 DCT
+    DCT4X8 = 12,
+    DCT8X4 = 13,
+
+    // Corner-DCT.
+    AFV0 = 14,
+
+    AFV1 = 15,
+    AFV2 = 16,
+    AFV3 = 17,
+
+    // Larger DCTs
+    DCT64X64 = 18,
+    DCT64X32 = 19,
+    DCT32X64 = 20,
+
+    // No transforms smaller than 64x64 are allowed below.
+    DCT128X128 = 21,
+    DCT128X64 = 22,
+    DCT64X128 = 23,
+    DCT256X256 = 24,
+    DCT256X128 = 25,
+    DCT128X256 = 26
+}
diff --git a/src/ImageSharp/Formats/Jxl/JxlFrameDimensions.cs b/src/ImageSharp/Formats/Jxl/JxlFrameDimensions.cs
new file mode 100644
index 0000000000..accd7d68cb
--- /dev/null
+++ b/src/ImageSharp/Formats/Jxl/JxlFrameDimensions.cs
@@ -0,0 +1,65 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Runtime.CompilerServices;
+
+namespace SixLabors.ImageSharp.Formats.Jxl;
+
+internal struct JxlFrameDimensions
+{
+    public const int BlockDimensions = 8;
+    public const int DctBlockSize = BlockDimensions * BlockDimensions;
+    public const int GroupDimensions = 256;
+    public const int GroupDimensionsInBlocks = GroupDimensions / BlockDimensions;
+
+    public int XSize;
+    public int YSize;
+    public int XSizeUpsampled;
+    public int YSizeUpsampled;
+    public int XSizeUpsampledPadded;
+    public int YSizeUpsampledPadded;
+    public int XSizePadded;
+    public int YSizePadded;
+    public int XSizeBlocks;
+    public int YSizeBlocks;
+    public int XSizeGroups;
+    public int YSizeGroups;
+    public int XSizeDcGroups;
+    public int YSizeDcGroups;
+    public int NumGroups;
+    public int NumDcGroups;
+    public int GroupDimension;
+    public int DcGroupDimension;
+
+    public JxlFrameDimensions(int xSizePixel, int ySizePixel, int groupSizeShift, int maxHorizontalShift, int maxVerticalShift, bool modularMode, int upsampling)
+    {
+        this.GroupDimension = (GroupDimensions >> 1) << groupSizeShift;
+        this.DcGroupDimension = this.GroupDimension * BlockDimensions;
+        this.XSizeUpsampled = xSizePixel;
+        this.YSizeUpsampled = ySizePixel;
+        this.XSize = DivCeil(xSizePixel, upsampling);
+        this.YSize = DivCeil(ySizePixel, upsampling);
+        this.XSizeBlocks = DivCeil(this.XSize, BlockDimensions << maxHorizontalShift) << maxHorizontalShift;
+        this.YSizeBlocks = DivCeil(this.YSize, BlockDimensions << maxVerticalShift) << maxVerticalShift;
+        this.XSizePadded = this.XSizeBlocks * BlockDimensions;
+        this.YSizePadded = this.YSizeBlocks * BlockDimensions;
+
+        if (modularMode)
+        {
+            this.XSizePadded = this.XSize;
+            this.YSizePadded = this.YSize;
+        }
+
+        this.XSizeUpsampledPadded = this.XSizePadded * upsampling;
+        this.YSizeUpsampledPadded = this.YSizePadded * upsampling;
+        this.XSizeGroups = DivCeil(this.XSize, GroupDimensions);
+        this.YSizeGroups = DivCeil(this.YSize, GroupDimensions);
+        this.XSizeDcGroups = DivCeil(this.XSizeBlocks, GroupDimensions);
+        this.YSizeDcGroups = DivCeil(this.YSizeBlocks, GroupDimensions);
+        this.NumGroups = this.XSizeGroups * this.YSizeGroups;
+        this.NumDcGroups = this.XSizeDcGroups * this.YSizeDcGroups;
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static int DivCeil(int x, int y) => x / y;
+}