diff --git a/src/ImageSharp/Formats/Heif/Av1/Av1BitStreamReader.cs b/src/ImageSharp/Formats/Heif/Av1/Av1BitStreamReader.cs
index 4dbbfe56e..99ba383ce 100644
--- a/src/ImageSharp/Formats/Heif/Av1/Av1BitStreamReader.cs
+++ b/src/ImageSharp/Formats/Heif/Av1/Av1BitStreamReader.cs
@@ -1,14 +1,16 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1;
 
 internal ref struct Av1BitStreamReader
 {
-    private const int WordSize = 32;
+    private const int WordSize = 1 << WordSizeLog2;
+    private const int WordSizeLog2 = 5;
+    private const int WordSizeInBytesLog2 = WordSizeLog2 - Log2Of8;
+    private const int Log2Of8 = 3;
 
     private readonly Span<uint> data;
     private uint currentWord;
@@ -175,11 +177,12 @@ internal ref struct Av1BitStreamReader
 
     public Span<byte> GetSymbolReader(int tileDataSize)
     {
-        DebugGuard.IsTrue((this.bitOffset & (WordSize - 1)) == 0, "Symbol reading needs to start on byte boundary.");
+        DebugGuard.IsTrue((this.bitOffset & 0x7) == 0, "Symbol reading needs to start on byte boundary.");
 
         // TODO: Pass exact byte iso Word start.
-        Span<uint> span = this.data.Slice(this.bitOffset >> WordSize, tileDataSize);
-        this.bitOffset += tileDataSize << 8;
+        int spanLength = tileDataSize >> WordSizeInBytesLog2;
+        Span<uint> span = this.data.Slice(this.bitOffset >> WordSizeLog2, spanLength);
+        this.bitOffset += tileDataSize << Log2Of8;
         return MemoryMarshal.Cast<uint, byte>(span);
     }
 }
diff --git a/src/ImageSharp/Formats/Heif/Av1/Av1Constants.cs b/src/ImageSharp/Formats/Heif/Av1/Av1Constants.cs
index d83389d9d..36e3d19c4 100644
--- a/src/ImageSharp/Formats/Heif/Av1/Av1Constants.cs
+++ b/src/ImageSharp/Formats/Heif/Av1/Av1Constants.cs
@@ -118,4 +118,9 @@ internal static class Av1Constants
     /// Number of segments allowed in segmentation map.
     /// </summary>
     public const int MaxSegments = 8;
+
+    /// <summary>
+    /// Number of reference frame types (including intra type).
+    /// </summary>
+    public const int TotalReferencesPerFrame = 8;
 }
diff --git a/src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuLoopFilterParameters.cs b/src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuLoopFilterParameters.cs
index ff510c8ae..ad32d0c01 100644
--- a/src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuLoopFilterParameters.cs
+++ b/src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuLoopFilterParameters.cs
@@ -5,6 +5,12 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
 internal class ObuLoopFilterParameters
 {
+    public ObuLoopFilterParameters()
+    {
+        this.ReferenceDeltas = [1, 0, 0, 0, 0, -1, -1, -1];
+        this.ModeDeltas = [0, 0];
+    }
+
     public int[] FilterLevel { get; internal set; } = new int[2];
 
     public int FilterLevelU { get; internal set; }
@@ -14,4 +20,10 @@ internal class ObuLoopFilterParameters
     public int SharpnessLevel { get; internal set; }
 
     public bool ReferenceDeltaModeEnabled { get; internal set; }
+
+    public bool ReferenceDeltaModeUpdate { get; internal set; }
+
+    public int[] ReferenceDeltas { get; }
+
+    public int[] ModeDeltas { get; }
 }
diff --git a/src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuReader.cs b/src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuReader.cs
index aa35df213..4823712f1 100644
--- a/src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuReader.cs
+++ b/src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuReader.cs
@@ -714,7 +714,7 @@ internal class ObuReader
         }
 
         frameInfo.DisableCdfUpdate = reader.ReadBoolean();
-        frameInfo.AllowScreenContentTools = sequenceHeader.ForceScreenContentTools == 1;
+        frameInfo.AllowScreenContentTools = sequenceHeader.ForceScreenContentTools == 2;
         if (frameInfo.AllowScreenContentTools)
         {
             frameInfo.AllowScreenContentTools = reader.ReadBoolean();
@@ -936,7 +936,7 @@ internal class ObuReader
         }
 
         frameInfo.AllLossless = frameInfo.CodedLossless && frameInfo.FrameSize.FrameWidth == frameInfo.FrameSize.SuperResolutionUpscaledWidth;
-        ReadLoopFilterParameters(ref reader, sequenceHeader, frameInfo, planesCount);
+        this.ReadLoopFilterParameters(ref reader, planesCount);
         ReadCdefParameters(ref reader, sequenceHeader, frameInfo, planesCount);
         ReadLoopRestorationParameters(ref reader, sequenceHeader, frameInfo, planesCount);
         ReadTransformMode(ref reader, frameInfo);
@@ -1024,7 +1024,7 @@ internal class ObuReader
         int tileGroupEnd = tileCount - 1;
         if (tileCount != 1 && tileStartAndEndPresentFlag)
         {
-            int tileBits = Av1Math.Log2(tileInfo.TileColumnCount) + Av1Math.Log2(tileInfo.TileRowCount);
+            int tileBits = tileInfo.TileColumnCountLog2 + tileInfo.TileRowCountLog2;
             tileGroupStart = (int)reader.ReadLiteral(tileBits);
             tileGroupEnd = (int)reader.ReadLiteral(tileBits);
         }
@@ -1196,8 +1196,9 @@ internal class ObuReader
     /// <summary>
     /// 5.9.11. Loop filter params syntax
     /// </summary>
-    private static void ReadLoopFilterParameters(ref Av1BitStreamReader reader, ObuSequenceHeader sequenceHeader, ObuFrameHeader frameInfo, int planesCount)
+    private void ReadLoopFilterParameters(ref Av1BitStreamReader reader, int planesCount)
     {
+        ObuFrameHeader frameInfo = this.FrameHeader!;
         frameInfo.LoopFilterParameters.FilterLevel = new int[2];
         if (frameInfo.CodedLossless || frameInfo.AllowIntraBlockCopy)
         {
@@ -1220,8 +1221,25 @@ internal class ObuReader
         frameInfo.LoopFilterParameters.ReferenceDeltaModeEnabled = reader.ReadBoolean();
         if (frameInfo.LoopFilterParameters.ReferenceDeltaModeEnabled)
         {
-            // TODO: Implement.
-            throw new NotImplementedException();
+            frameInfo.LoopFilterParameters.ReferenceDeltaModeUpdate = reader.ReadBoolean();
+            if (frameInfo.LoopFilterParameters.ReferenceDeltaModeUpdate)
+            {
+                for (int i = 0; i < Av1Constants.TotalReferencesPerFrame; i++)
+                {
+                    if (reader.ReadBoolean())
+                    {
+                        frameInfo.LoopFilterParameters.ReferenceDeltas[i] = reader.ReadSignedFromUnsigned(7);
+                    }
+                }
+
+                for (int i = 0; i < 2; i++)
+                {
+                    if (reader.ReadBoolean())
+                    {
+                        frameInfo.LoopFilterParameters.ModeDeltas[i] = reader.ReadSignedFromUnsigned(7);
+                    }
+                }
+            }
         }
     }