Replaced hardcoded values with actual calculated ones in postprocessor

src/ImageSharp/Formats/Jpeg/Components/Decoder/JpegComponentPostProcessor.cs

@@ -37,7 +37,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                 imagePostProcessor.PostProcessorBufferSize.Height,
                 this.blockAreaSize.Height);
 
-            this.BlockRowsPerStep = JpegImagePostProcessor.BlockRowsPerStep / this.Component.SubSamplingDivisors.Height;
+            this.BlockRowsPerStep = imagePostProcessor.BlockRowsPerStep / this.Component.SubSamplingDivisors.Height;
         }
 
         /// <summary>

src/ImageSharp/Formats/Jpeg/Components/Decoder/JpegImagePostProcessor.cs

@@ -29,12 +29,12 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// <summary>
         /// The number of block rows to be processed in one Step.
         /// </summary>
-        public const int BlockRowsPerStep = 4;
+        public int BlockRowsPerStep;
 
         /// <summary>
         /// The number of image pixel rows to be processed in one step.
         /// </summary>
-        public const int PixelRowsPerStep = 4 * 8;
+        public int PixelRowsPerStep;
 
         /// <summary>
         /// Temporal buffer to store a row of colors.
@@ -56,8 +56,13 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             this.configuration = configuration;
             this.RawJpeg = rawJpeg;
             IJpegComponent c0 = rawJpeg.Components[0];
-            this.NumberOfPostProcessorSteps = c0.SizeInBlocks.Height / BlockRowsPerStep;
-            this.PostProcessorBufferSize = new Size(c0.SizeInBlocks.Width * 8, PixelRowsPerStep);
+
+            this.BlockRowsPerStep = c0.SamplingFactors.Height;
+            this.PixelRowsPerStep = this.BlockRowsPerStep * 8;
+
+            this.NumberOfPostProcessorSteps = c0.SizeInBlocks.Height / this.BlockRowsPerStep;
+
+            this.PostProcessorBufferSize = new Size(c0.SizeInBlocks.Width * 8, this.PixelRowsPerStep);
 
             MemoryAllocator memoryAllocator = configuration.MemoryAllocator;
 

tests/ImageSharp.Tests.ProfilingSandbox/Program.cs

@@ -58,7 +58,6 @@ namespace SixLabors.ImageSharp.Tests.ProfilingSandbox
             //Test_DebugRun("Channel_digital_image_CMYK_color");
             //Console.WriteLine();
 
-
             //Test_DebugRun("test_baseline_4k_444", false);
             //Console.WriteLine();
             //Test_DebugRun("test_progressive_4k_444", false);
@@ -69,6 +68,10 @@ namespace SixLabors.ImageSharp.Tests.ProfilingSandbox
             // Binary size of this must be ~2096kb
             //Test_DebugRun("422", true);
 
+            //Test_DebugRun("baseline_4k_420", false);
+            //Test_DebugRun("baseline_s444_q100", false);
+            //Test_DebugRun("progressive_s444_q100", false);
+            Test_DebugRun("baseline_4k_420", true);
             Test_DebugRun("baseline_s444_q100", true);
             Test_DebugRun("progressive_s444_q100", true);