diff --git a/src/ImageSharp/Formats/Jxl/Processing/Decoder/JxlGroupDecoderCache.cs b/src/ImageSharp/Formats/Jxl/Processing/Decoder/JxlGroupDecoderCache.cs
new file mode 100644
index 000000000..f82e332d8
--- /dev/null
+++ b/src/ImageSharp/Formats/Jxl/Processing/Decoder/JxlGroupDecoderCache.cs
@@ -0,0 +1,12 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Processing.Decoder;
+
+/// <summary>
+/// Cache for the JPEG XL Group Decoder.
+/// </summary>
+internal sealed class JxlGroupDecoderCache
+{
+
+}
diff --git a/src/ImageSharp/Formats/Jxl/Processing/Decoder/JxlPassesDecoderState.cs b/src/ImageSharp/Formats/Jxl/Processing/Decoder/JxlPassesDecoderState.cs
new file mode 100644
index 000000000..5b534ef77
--- /dev/null
+++ b/src/ImageSharp/Formats/Jxl/Processing/Decoder/JxlPassesDecoderState.cs
@@ -0,0 +1,77 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Jxl.IO.FrameHeader;
+using SixLabors.ImageSharp.Formats.Jxl.Memory.ImageTypes;
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Processing.Decoder;
+
+internal sealed class JxlPassesDecoderState
+{
+    public JxlPassesDecoderState(JxlFrameHeader header, Configuration configuration)
+    {
+        this.XDmMultiplier = MathF.Pow(1 / 1.25f, header.XQmScale - 2f);
+        this.BDmMultiplier = MathF.Pow(1 / 1.25f, header.BQmScale - 2f);
+
+        this.MainOutput.Callback = PixelCallback;
+        this.MainOutput.Buffer = null;
+
+        this.UndoOrientation = JxlOrientation.Identity;
+        this.Upsampler8x = GetUpsamplingImage(configuration, this.Shared.CodecMetadata.CustomTransformData, 0, 3);
+
+        if (header.LoopFilter?.EpfIterations > 0)
+        {
+            this.Sigma = new JxlImageF(
+                configuration,
+                (this.Shared.FrameDimensions.XSizeBlocks + 2) * SigmaPadding,
+                (this.Shared.FrameDimensions.YSizeBlocks + 2) * SigmaPadding);
+        }
+
+        this.SharedStorage = new(configuration, header, false);
+        this.Shared = this.SharedStorage;
+    }
+
+    public JxlPassesSharedState SharedStorage { get; set; }
+
+    public JxlPassesSharedState Shared { get; set; }
+
+    public JxlRenderPipelineStage[] Upsampler8x { get; set; } = [];
+
+    public List<JxlAnsCode> Code { get; set; } = [];
+
+    public List<List<byte>> ContextMap { get; set; } = [];
+
+    public float XDmMultiplier { get; set; }
+
+    public float BDmMultiplier { get; set; }
+
+    public JxlImageF? Sigma { get; set; }
+
+    public int Width { get; set; }
+
+    public int Height { get; set; }
+
+    public JxlImageOutput MainOutput { get; set; }
+
+    public List<JxlImageOutput> ExtraOutput { get; set; } = [];
+
+    public bool FastXybSRgb8Conversion { get; set; }
+
+    public bool UnpremultiplyAlpha { get; set; }
+
+    public JxlOrientation UndoOrientation { get; set; }
+
+    public int VisibleFrameIndex { get; set; }
+
+    public int NonvisibleFrameIndex { get; set; }
+
+    public int UsedAcs { get; set; }
+
+    public JxlDctAcImage<int> Coefficients { get; set; } = [];
+
+    public JxlRenderPipeline RenderPipeline { get; set; }
+
+    public JxlImageBundle FrameStorageForReferencing { get; set; }
+
+    public JxlOutputEncodingInfo OutputEncodingInfo { get; set; } = new();
+}
diff --git a/src/ImageSharp/Formats/Jxl/Processing/Splines/JxlQuantizedSpline.cs b/src/ImageSharp/Formats/Jxl/Processing/Splines/JxlQuantizedSpline.cs
index ed5729067..40dff40e2 100644
--- a/src/ImageSharp/Formats/Jxl/Processing/Splines/JxlQuantizedSpline.cs
+++ b/src/ImageSharp/Formats/Jxl/Processing/Splines/JxlQuantizedSpline.cs
@@ -3,6 +3,7 @@
 
 using System.Buffers;
 using System.Runtime.CompilerServices;
+using SixLabors.ImageSharp.Formats.Jxl.Processing.Decoder;
 
 namespace SixLabors.ImageSharp.Formats.Jxl.Processing.Splines;
 
@@ -269,8 +270,8 @@ internal sealed class JxlQuantizedSpline : IDisposable
         {
             ref JxlControlPoint controlPoint = ref controlPoints[i];
 
-            controlPoint.First = UnpackSigned(decoder.ReadHybridUnsignedInteger(ControlPointsContext, br, contextMap));
-            controlPoint.Second = UnpackSigned(decoder.ReadHybridUnsignedInteger(ControlPointsContext, br, contextMap));
+            controlPoint.First = JxlPackSigned.UnpackSigned(decoder.ReadHybridUnsignedInteger(ControlPointsContext, br, contextMap));
+            controlPoint.Second = JxlPackSigned.UnpackSigned(decoder.ReadHybridUnsignedInteger(ControlPointsContext, br, contextMap));
 
             if (controlPoint.First >= deltaLimit || controlPoint.First <= -deltaLimit ||
                 controlPoint.Second >= deltaLimit || controlPoint.Second <= -deltaLimit)
@@ -300,7 +301,7 @@ internal sealed class JxlQuantizedSpline : IDisposable
 
             for (int i = 0; i < 32; i++)
             {
-                dct[i] = UnpackSigned(decoder.ReadHybridUnsignedInteger(DctContext, br, contextMap));
+                dct[i] = JxlPackSigned.UnpackSigned(decoder.ReadHybridUnsignedInteger(DctContext, br, contextMap));
                 if (dct[i] == invalidCoefficient)
                 {
                     throw new InvalidOperationException("The DCT coefficient is invalid");