more subsampling refactor

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

@@ -1,5 +1,7 @@
 namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
 {
+    using SixLabors.Primitives;
+
     /// <summary>
     /// Provides enumeration of the various available subsample ratios.
     /// https://en.wikipedia.org/wiki/Chroma_subsampling
@@ -64,5 +66,32 @@
 
             return SubsampleRatio.Ratio444;
         }
+
+        /// <summary>
+        /// Returns the height and width of the chroma components
+        /// </summary>
+        /// <param name="ratio">The subsampling ratio.</param>
+        /// <param name="width">The width.</param>
+        /// <param name="height">The height.</param>
+        /// <returns>The <see cref="Size"/> of the chrominance channel</returns>
+        public static Size CalculateChrominanceSize(this SubsampleRatio ratio, int width, int height)
+        {
+            switch (ratio)
+            {
+                case SubsampleRatio.Ratio422:
+                    return new Size((width + 1) / 2, height);
+                case SubsampleRatio.Ratio420:
+                    return new Size((width + 1) / 2, (height + 1) / 2);
+                case SubsampleRatio.Ratio440:
+                    return new Size(width, (height + 1) / 2);
+                case SubsampleRatio.Ratio411:
+                    return new Size((width + 3) / 4, height);
+                case SubsampleRatio.Ratio410:
+                    return new Size((width + 3) / 4, (height + 1) / 2);
+                default:
+                    // Default to 4:4:4 subsampling.
+                    return new Size(width, height);
+            }
+        }
     }
 }

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

@@ -38,7 +38,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
         /// <param name="ratio">The ratio.</param>
         public YCbCrImage(int width, int height, SubsampleRatio ratio)
         {
-            Size cSize = CalculateChrominanceSize(width, height, ratio);
+            Size cSize = ratio.CalculateChrominanceSize(width, height);
 
             this.Ratio = ratio;
             this.YStride = width;
@@ -112,35 +112,5 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
         {
             return y * this.YStride;
         }
-
-        /// <summary>
-        /// Returns the height and width of the chroma components
-        /// </summary>
-        /// <param name="width">The width.</param>
-        /// <param name="height">The height.</param>
-        /// <param name="ratio">The subsampling ratio.</param>
-        /// <returns>The <see cref="Size"/> of the chrominance channel</returns>
-        internal static Size CalculateChrominanceSize(
-            int width,
-            int height,
-            SubsampleRatio ratio)
-        {
-            switch (ratio)
-            {
-                case SubsampleRatio.Ratio422:
-                    return new Size((width + 1) / 2, height);
-                case SubsampleRatio.Ratio420:
-                    return new Size((width + 1) / 2, (height + 1) / 2);
-                case SubsampleRatio.Ratio440:
-                    return new Size(width, (height + 1) / 2);
-                case SubsampleRatio.Ratio411:
-                    return new Size((width + 3) / 4, height);
-                case SubsampleRatio.Ratio410:
-                    return new Size((width + 3) / 4, (height + 1) / 2);
-                default:
-                    // Default to 4:4:4 subsampling.
-                    return new Size(width, height);
-            }
-        }
     }
 }

tests/ImageSharp.Tests/Formats/Jpg/YCbCrImageTests.cs → tests/ImageSharp.Tests/Formats/Jpg/SubsampleRatioTests.cs

@@ -9,9 +9,9 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
     using Xunit;
     using Xunit.Abstractions;
 
-    public class YCbCrImageTests
+    public class SubsampleRatioTests
     {
-        public YCbCrImageTests(ITestOutputHelper output)
+        public SubsampleRatioTests(ITestOutputHelper output)
         {
             this.Output = output;
         }
@@ -31,7 +31,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
             int expectedDivY)
         {
             //this.Output.WriteLine($"RATIO: {ratio}");
-            Size size = YCbCrImage.CalculateChrominanceSize(400, 400, ratio);
+            Size size = ratio.CalculateChrominanceSize(400, 400);
             //this.Output.WriteLine($"Ch Size: {size}");
 
             Assert.Equal(new Size(400 / expectedDivX, 400 / expectedDivY), size);