test Ycck as well ..

src/ImageSharp/Formats/Jpeg/GolangPort/Components/Decoder/OrigComponent.cs

@@ -7,6 +7,8 @@ using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
 {
+    using SixLabors.Primitives;
+
     /// <summary>
     /// Represents a single color component
     /// </summary>
@@ -222,6 +224,20 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
             this.VerticalSamplingFactor = v;
         }
 
+        public Size CalculateJpegChannelSize(SubsampleRatio ratio)
+        {
+            Size size = new Size(this.WidthInBlocks, this.HeightInBlocks) * 8;
+
+            if (this.Index > 0 && this.Index < 3) // Chroma component:
+            {
+                return ratio.CalculateChrominanceSize(size.Width, size.Height);
+            }
+            else
+            {
+                return size;
+            }
+        }
+
         public void Dispose()
         {
             this.SpectralBlocks.Dispose();

src/ImageSharp/Formats/Jpeg/GolangPort/Components/Decoder/SubsampleRatio.cs

@@ -1,11 +1,10 @@
-namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
-{
-    using System.Collections.Generic;
-    using System.Linq;
-
-    using SixLabors.ImageSharp.Formats.Jpeg.Common;
-    using SixLabors.Primitives;
+using System.Collections.Generic;
+using System.Linq;
+using SixLabors.ImageSharp.Formats.Jpeg.Common;
+using SixLabors.Primitives;
 
+namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
+{
     /// <summary>
     /// Provides enumeration of the various available subsample ratios.
     /// https://en.wikipedia.org/wiki/Chroma_subsampling

src/ImageSharp/Formats/Jpeg/GolangPort/OrigJpegDecoderCore.cs

@@ -203,10 +203,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
             where TPixel : struct, IPixel<TPixel>
         {
             this.ParseStream(stream);
-            this.ProcessBlocksIntoJpegImageChannels<TPixel>();
-            Image<TPixel> image = this.ConvertJpegPixelsToImagePixels<TPixel>();
 
-            return image;
+            this.ProcessBlocksIntoJpegImageChannels();
+
+            return this.ConvertJpegPixelsToImagePixels<TPixel>();
         }
 
         /// <inheritdoc />
@@ -464,9 +464,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
         /// <see cref="OrigComponent.SpectralBlocks"/> are in a "raw" frequency-domain form. We need to apply IDCT, dequantization and unzigging to transform them into color-space blocks.
         /// We can copy these blocks into <see cref="OrigJpegPixelArea"/>-s afterwards.
         /// </summary>
-        /// <typeparam name="TPixel">The pixel type</typeparam>
-        private void ProcessBlocksIntoJpegImageChannels<TPixel>()
-            where TPixel : struct, IPixel<TPixel>
+        private void ProcessBlocksIntoJpegImageChannels()
         {
             this.InitJpegImageChannels();
 

tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.cs

@@ -24,8 +24,11 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
     {
         public static string[] BaselineTestJpegs =
             {
-                TestImages.Jpeg.Baseline.Calliphora, TestImages.Jpeg.Baseline.Cmyk,
-                TestImages.Jpeg.Baseline.Jpeg400, TestImages.Jpeg.Baseline.Jpeg444,
+                TestImages.Jpeg.Baseline.Calliphora,
+                TestImages.Jpeg.Baseline.Cmyk,
+                TestImages.Jpeg.Baseline.Ycck,
+                TestImages.Jpeg.Baseline.Jpeg400,
+                TestImages.Jpeg.Baseline.Jpeg444,
                 TestImages.Jpeg.Baseline.Testimgorig,
                 TestImages.Jpeg.Baseline.Bad.BadEOF,
                 TestImages.Jpeg.Baseline.Bad.ExifUndefType,

tests/Images/External

@@ -1 +1 @@
-Subproject commit 3b80ee0684fedab0f5798eea5c5ed7b75cbff714
+Subproject commit 2f6b226b9fbaf8b23808755bd7e7752a0560644e