Scan order unit test and fixes

src/ImageSharp/Formats/Heif/Av1/Transform/Av1ScanOrder.cs

@@ -8,20 +8,20 @@ internal readonly struct Av1ScanOrder
     public Av1ScanOrder(short[] scan)
     {
         this.Scan = scan;
-        this.IScan = [];
+        this.InverseScan = [];
         this.Neighbors = [];
     }
 
-    public Av1ScanOrder(short[] scan, short[] iscan, short[] neighbors)
+    public Av1ScanOrder(short[] scan, short[] inverseScan, short[] neighbors)
     {
         this.Scan = scan;
-        this.IScan = iscan;
+        this.InverseScan = inverseScan;
         this.Neighbors = neighbors;
     }
 
     public short[] Scan { get; }
 
-    public short[] IScan { get; }
+    public short[] InverseScan { get; }
 
     public short[] Neighbors { get; }
 }

src/ImageSharp/Formats/Heif/Av1/Transform/Av1TransformSizeExtensions.cs

@@ -141,13 +141,9 @@ internal static class Av1TransformSizeExtensions
         return (pels > 1024) ? 2 : (pels > 256) ? 1 : 0;
     }
 
-    public static int GetWidth(this Av1TransformSize size) => (int)size;
+    public static int GetWidth(this Av1TransformSize size) => WideUnit[(int)size] << 2;
 
-    public static int GetHeight(this Av1TransformSize size) => (int)size;
-
-    public static int GetWidthLog2(this Av1TransformSize size) => (int)size;
-
-    public static int GetHeightLog2(this Av1TransformSize size) => (int)size;
+    public static int GetHeight(this Av1TransformSize size) => HighUnit[(int)size] << 2;
 
     public static int Get4x4WideCount(this Av1TransformSize size) => WideUnit[(int)size];
 

tests/ImageSharp.Tests/Formats/Heif/Av1/Av1ScanOrderTests.cs

@@ -28,6 +28,43 @@ public class Av1ScanOrderTests
         }
     }
 
+    [Theory]
+    [MemberData(nameof(GetCombinations))]
+    internal void AllIndicesScannedAreWithinRange(int s, int t)
+    {
+        // Assign
+        Av1TransformSize transformSize = (Av1TransformSize)s;
+        Av1TransformType transformType = (Av1TransformType)t;
+        int lowValue = 0;
+
+        // Act
+        Av1ScanOrder scanOrder = Av1ScanOrderConstants.GetScanOrder(transformSize, transformType);
+        int highValue = scanOrder.Scan.Length - 1;
+
+        // Assert
+        foreach (short scan in scanOrder.Scan)
+        {
+            Assert.InRange(scan, lowValue, highValue);
+        }
+    }
+
+    [Theory]
+    [MemberData(nameof(GetCombinations))]
+    internal void CorrectNumberOfIndicesScanned(int s, int t)
+    {
+        // Assign
+        Av1TransformSize transformSize = (Av1TransformSize)s;
+        Av1TransformType transformType = (Av1TransformType)t;
+        int width = Math.Min(transformSize.GetWidth(), 32);
+        int height = Math.Min(transformSize.GetHeight(), 32);
+
+        // Act
+        Av1ScanOrder scanOrder = Av1ScanOrderConstants.GetScanOrder(transformSize, transformType);
+
+        // Assert
+        Assert.Equal(width * height, scanOrder.Scan.Length);
+    }
+
     public static TheoryData<int, int> GetCombinations()
     {
         TheoryData<int, int> combinations = [];