Update tests

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -350,7 +350,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
                 localColorTableFlag: hasColorTable,
                 interfaceFlag: false,
                 sortFlag: false,
-                localColorTableSize: (byte)(this.bitDepth - 1)); // Note: we subtract 1 from the colorTableSize writing
+                localColorTableSize: (byte)this.bitDepth);
 
             var descriptor = new GifImageDescriptor(
                 left: 0,

tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs

@@ -117,5 +117,31 @@ namespace SixLabors.ImageSharp.Tests.Formats.Gif
                 }
             }
         }
+
+        [Theory]
+        [WithFile(TestImages.Gif.Cheers, PixelTypes.Rgba32)]
+        public void EncodeGlobalPaletteReturnsSmallerFile<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            using (Image<TPixel> image = provider.GetImage())
+            {
+                var encoder = new GifEncoder
+                {
+                    ColorTableMode = GifColorTableMode.Global,
+                    Quantizer = new OctreeQuantizer(false)
+                };
+
+                // Always save as we need to compare the encoded output.
+                provider.Utility.SaveTestOutputFile(image, "gif", encoder, "global");
+
+                encoder.ColorTableMode = GifColorTableMode.Local;
+                provider.Utility.SaveTestOutputFile(image, "gif", encoder, "local");
+
+                var fileInfoGlobal = new FileInfo(provider.Utility.GetTestOutputFileName("gif", "global"));
+                var fileInfoLocal = new FileInfo(provider.Utility.GetTestOutputFileName("gif", "local"));
+
+                Assert.True(fileInfoGlobal.Length < fileInfoLocal.Length);
+            }
+        }
     }
 }

tests/Images/External

@@ -1 +1 @@
-Subproject commit 6fcee2ccd5e8bac98a0290b467ad86bb02d00b6c
+Subproject commit fa43e075a78d041c6fc7a52da96b23adf0e8775a