Fix for Issue #1505

src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs

@@ -6,7 +6,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
@@ -96,7 +95,7 @@ public void AddPaletteColors(Buffer2DRegion<TPixel> pixelRegion)
             this.octree.Palletize(paletteSpan, this.maxColors, ref paletteIndex);
 
             // Length of reduced palette + transparency.
-            ReadOnlyMemory<TPixel> result = this.paletteOwner.Memory.Slice(0, Math.Min(paletteIndex + 2, QuantizerConstants.MaxColors));
+            ReadOnlyMemory<TPixel> result = this.paletteOwner.Memory.Slice(0, Math.Min(paletteIndex + 2, this.maxColors));
             this.pixelMap = new EuclideanPixelMap<TPixel>(this.Configuration, result);
 
             this.palette = result;

tests/ImageSharp.Tests/Quantization/QuantizedImageTests.cs

@@ -110,6 +110,21 @@ public void WuQuantizerYieldsCorrectTransparentPixel<TPixel>(TestImageProvider<T
             }
         }
 
+        // Test case for issue: https://github.com/SixLabors/ImageSharp/issues/1505
+        [Theory]
+        [WithFile(TestImages.Gif.Issues.Issue1505, PixelTypes.Rgba32)]
+        public void Issue1505<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            using (Image<TPixel> image = provider.GetImage())
+            {
+                var octreeQuantizer = new OctreeQuantizer();
+                IQuantizer<TPixel> quantizer = octreeQuantizer.CreatePixelSpecificQuantizer<TPixel>(Configuration.Default, new QuantizerOptions() { MaxColors = 128 });
+                ImageFrame<TPixel> frame = image.Frames[0];
+                quantizer.BuildPaletteAndQuantizeFrame(frame, frame.Bounds());
+            }
+        }
+
         private int GetTransparentIndex<TPixel>(IndexedImageFrame<TPixel> quantized)
             where TPixel : unmanaged, IPixel<TPixel>
         {

tests/ImageSharp.Tests/TestImages.cs

@@ -415,6 +415,7 @@ public static class Issues
                 public const string BadAppExtLength = "Gif/issues/issue405_badappextlength252.gif";
                 public const string BadAppExtLength_2 = "Gif/issues/issue405_badappextlength252-2.gif";
                 public const string BadDescriptorWidth = "Gif/issues/issue403_baddescriptorwidth.gif";
+                public const string Issue1505 = "Gif/issues/issue1505_argumentoutofrange.png";
             }
 
             public static readonly string[] All = { Rings, Giphy, Cheers, Trans, Kumin, Leo, Ratio4x1, Ratio1x4 };