several refactors

src/ImageSharp/Formats/Jpeg/Common/ComponentUtils.cs

@@ -1,17 +1,23 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Linq;
+using System.Numerics;
 using SixLabors.Primitives;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.Common
 {
-    using System;
-
     /// <summary>
     /// Various utilities for <see cref="SubsampleRatio"/> and <see cref="IJpegComponent"/>.
     /// </summary>
     internal static class ComponentUtils
     {
-        public static Size SizeInBlocks(this IJpegComponent component) => new Size(component.WidthInBlocks, component.HeightInBlocks);
+        //public static Size SizeInBlocks(this IJpegComponent component) => new Size(component.WidthInBlocks, component.HeightInBlocks);
+
+        // In Jpeg these are really useful operations:
+
+        public static Size MultiplyBy(this Size a, Size b) => new Size(a.Width * b.Width, a.Height * b.Height);
+
+        public static Size DivideBy(this Size a, Size b) => new Size(a.Width / b.Width, a.Height / b.Height);
 
         public static ref Block8x8 GetBlockReference(this IJpegComponent component, int bx, int by)
         {
@@ -39,16 +45,16 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common
             return SubsampleRatio.Ratio444;
         }
 
+        // https://en.wikipedia.org/wiki/Chroma_subsampling
         public static SubsampleRatio GetSubsampleRatio(IEnumerable<IJpegComponent> components)
         {
             IJpegComponent[] componentArray = components.ToArray();
             if (componentArray.Length == 3)
             {
-                int h0 = componentArray[0].HorizontalSamplingFactor;
+                Size s0 = componentArray[0].SamplingFactors;
-                int v0 = componentArray[0].VerticalSamplingFactor;
+                Size ratio = s0.DivideBy(componentArray[1].SamplingFactors);
-                int horizontalRatio = h0 / componentArray[1].HorizontalSamplingFactor;
+
-                int verticalRatio = v0 / componentArray[1].VerticalSamplingFactor;
+                return GetSubsampleRatio(ratio.Width, ratio.Height);
-                return GetSubsampleRatio(horizontalRatio, verticalRatio);
             }
             else
             {
@@ -58,40 +64,57 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common
 
         /// <summary>
         /// Returns the height and width of the chroma components
+        /// TODO: Not needed by new JpegImagePostprocessor
         /// </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)
+        {
+            (int divX, int divY) = ratio.GetChrominanceSubSampling();
+            var size = new Size(width, height);
+            return size.GetSubSampledSize(divX, divY);
+        }
+
+        // TODO: Find a better place for this method
+        public static Size GetSubSampledSize(this Size originalSize, int divX, int divY)
+        {
+            var sizeVect = (Vector2)(SizeF)originalSize;
+            sizeVect /= new Vector2(divX, divY);
+            sizeVect.X = MathF.Ceiling(sizeVect.X);
+            sizeVect.Y = MathF.Ceiling(sizeVect.Y);
+
+            return new Size((int)sizeVect.X, (int)sizeVect.Y);
+        }
+
+        public static Size GetSubSampledSize(this Size originalSize, int subsamplingDivisor) =>
+            GetSubSampledSize(originalSize, subsamplingDivisor, subsamplingDivisor);
+
+        // TODO: Not needed by new JpegImagePostprocessor
+        public static (int divX, int divY) GetChrominanceSubSampling(this SubsampleRatio ratio)
         {
             switch (ratio)
             {
-                case SubsampleRatio.Ratio422:
+                case SubsampleRatio.Ratio422: return (2, 1);
-                    return new Size((width + 1) / 2, height);
+                case SubsampleRatio.Ratio420: return (2, 2);
-                case SubsampleRatio.Ratio420:
+                case SubsampleRatio.Ratio440: return (1, 2);
-                    return new Size((width + 1) / 2, (height + 1) / 2);
+                case SubsampleRatio.Ratio411: return (4, 1);
-                case SubsampleRatio.Ratio440:
+                case SubsampleRatio.Ratio410: return (4, 2);
-                    return new Size(width, (height + 1) / 2);
+                default: return (1, 1);
-                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);
             }
         }
 
         public static bool IsChromaComponent(this IJpegComponent component) =>
             component.Index > 0 && component.Index < 3;
 
+        // TODO: Not needed by new JpegImagePostprocessor
         public static Size[] CalculateJpegChannelSizes(IEnumerable<IJpegComponent> components, SubsampleRatio ratio)
         {
             IJpegComponent[] c = components.ToArray();
             Size[] sizes = new Size[c.Length];
 
-            Size s0 = new Size(c[0].WidthInBlocks, c[0].HeightInBlocks) * 8;
+            Size s0 = c[0].SizeInBlocks * 8;
             sizes[0] = s0;
 
             if (c.Length > 1)

src/ImageSharp/Formats/Jpeg/Common/IJpegComponent.cs

@@ -1,4 +1,5 @@
 using SixLabors.ImageSharp.Memory;
+using SixLabors.Primitives;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.Common
 {
@@ -13,24 +14,23 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common
         int Index { get; }
 
         /// <summary>
-        /// Gets the number of blocks per line
+        /// Gets the number of blocks in this component as <see cref="Size"/>
         /// </summary>
-        int WidthInBlocks { get; }
+        Size SizeInBlocks { get; }
 
         /// <summary>
-        /// Gets the number of blocks per column
+        /// Gets the horizontal and the vertical sampling factor as <see cref="Size"/>
         /// </summary>
-        int HeightInBlocks { get; }
+        Size SamplingFactors { get; }
 
         /// <summary>
-        /// Gets the horizontal sampling factor.
+        /// Gets the divisors needed to apply when calculating colors.
+        /// <see>
+        ///     <cref>https://en.wikipedia.org/wiki/Chroma_subsampling</cref>
+        /// </see>
+        /// In case of 4:2:0 subsampling the values are: Luma.SubSamplingDivisors = (1,1) Chroma.SubSamplingDivisors = (2,2)
         /// </summary>
-        int HorizontalSamplingFactor { get; }
+        Size SubSamplingDivisors { get; }
-
-        /// <summary>
-        /// Gets the vertical sampling factor.
-        /// </summary>
-        int VerticalSamplingFactor { get; }
 
         /// <summary>
         /// Gets the index of the quantization table for this block.

src/ImageSharp/Formats/Jpeg/Common/IRawJpegData.cs

@@ -7,6 +7,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common
     {
         Size ImageSizeInPixels { get; }
 
+        // TODO: Kill this
         Size ImageSizeInBlocks { get; }
 
         int ComponentCount { get; }

src/ImageSharp/Formats/Jpeg/Common/PostProcessing/JpegComponentPostProcessor.cs

@@ -1,11 +1,10 @@
 using System;
+using SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder;
 using SixLabors.ImageSharp.Memory;
+using SixLabors.Primitives;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.Common.PostProcessing
 {
-    using SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder;
-    using SixLabors.Primitives;
-
     internal class JpegComponentPostProcessor : IDisposable
     {
         private int currentComponentRowInBlocks;
@@ -18,8 +17,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common.PostProcessing
             this.ImagePostProcessor = imagePostProcessor;
             this.ColorBuffer = new Buffer2D<float>(imagePostProcessor.PostProcessorBufferSize);
 
-            this.BlockRowsPerStep = JpegImagePostProcessor.BlockRowsPerStep / this.VerticalSamplingFactor;
+            this.BlockRowsPerStep = JpegImagePostProcessor.BlockRowsPerStep / this.Component.SubSamplingDivisors.Height;
-            this.blockAreaSize = new Size(this.HorizontalSamplingFactor, this.VerticalSamplingFactor) * 8;
+            this.blockAreaSize = this.Component.SubSamplingDivisors * 8;
         }
 
         public JpegImagePostProcessor ImagePostProcessor { get; }
@@ -28,14 +27,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common.PostProcessing
 
         public Buffer2D<float> ColorBuffer { get; }
 
-        public int BlocksPerRow => this.Component.WidthInBlocks;
+        public Size SizeInBlocks => this.Component.SizeInBlocks;
 
         public int BlockRowsPerStep { get; }
 
-        private int HorizontalSamplingFactor => this.Component.HorizontalSamplingFactor;
-
-        private int VerticalSamplingFactor => this.Component.VerticalSamplingFactor;
-
         public void Dispose()
         {
             this.ColorBuffer.Dispose();
@@ -49,9 +44,15 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common.PostProcessing
             for (int y = 0; y < this.BlockRowsPerStep; y++)
             {
                 int yBlock = this.currentComponentRowInBlocks + y;
+
+                if (yBlock >= this.SizeInBlocks.Height)
+                {
+                    break;
+                }
+
                 int yBuffer = y * this.blockAreaSize.Height;
 
-                for (int x = 0; x < this.BlocksPerRow; x++)
+                for (int x = 0; x < this.SizeInBlocks.Width; x++)
                 {
                     int xBlock = x;
                     int xBuffer = x * this.blockAreaSize.Width;

src/ImageSharp/Formats/Jpeg/Common/SubsampleRatio.cs

@@ -3,6 +3,7 @@
     /// <summary>
     /// Provides enumeration of the various available subsample ratios.
     /// https://en.wikipedia.org/wiki/Chroma_subsampling
+    /// TODO: Not needed by new JpegImagePostprocessor
     /// </summary>
     internal enum SubsampleRatio
     {

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

@@ -25,7 +25,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
         /// Pointers to elements of <see cref="data"/>
         /// </summary>
         private DataPointers pointers;
-        
+
         /// <summary>
         /// Initialize the <see cref="JpegBlockPostProcessor"/> instance on the stack.
         /// </summary>
@@ -43,9 +43,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
         /// <param name="component">The component</param>
         public void ProcessAllBlocks(OrigJpegDecoderCore decoder, IJpegComponent component)
         {
-            for (int by = 0; by < component.HeightInBlocks; by++)
+            for (int by = 0; by < component.SizeInBlocks.Height; by++)
             {
-                for (int bx = 0; bx < component.WidthInBlocks; bx++)
+                for (int bx = 0; bx < component.SizeInBlocks.Width; bx++)
                 {
                     this.ProcessBlockColors(decoder, component, bx, by);
                 }

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;
+
     /// <inheritdoc cref="IJpegComponent" />
     /// <summary>
     /// Represents a single color component
@@ -27,11 +29,15 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
         /// <inheritdoc />
         public int Index { get; }
 
-        /// <inheritdoc />
+        public Size SizeInBlocks { get; private set; }
-        public int HorizontalSamplingFactor { get; private set; }
 
-        /// <inheritdoc />
+        public Size SamplingFactors { get; private set; }
-        public int VerticalSamplingFactor { get; private set; }
+
+        public Size SubSamplingDivisors { get; private set; } = new Size(1, 1);
+
+        public int HorizontalSamplingFactor => this.SamplingFactors.Width;
+
+        public int VerticalSamplingFactor => this.SamplingFactors.Height;
 
         /// <inheritdoc />
         public int QuantizationTableIndex { get; private set; }
@@ -45,28 +51,28 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
         /// </summary>
         public Buffer2D<Block8x8> SpectralBlocks { get; private set; }
 
-        /// <inheritdoc />
-        public int WidthInBlocks { get; private set; }
-
-        /// <inheritdoc />
-        public int HeightInBlocks { get; private set; }
-
         /// <summary>
         /// Initializes <see cref="SpectralBlocks"/>
         /// </summary>
         /// <param name="decoder">The <see cref="OrigJpegDecoderCore"/> instance</param>
-        public void InitializeBlocks(OrigJpegDecoderCore decoder)
+        public void InitializeDerivedData(OrigJpegDecoderCore decoder)
         {
-            this.WidthInBlocks = decoder.MCUCountX * this.HorizontalSamplingFactor;
+            this.SizeInBlocks = decoder.ImageSizeInBlocks.MultiplyBy(this.SamplingFactors);
-            this.HeightInBlocks = decoder.MCUCountY * this.VerticalSamplingFactor;
+
-            this.SpectralBlocks = Buffer2D<Block8x8>.CreateClean(this.WidthInBlocks, this.HeightInBlocks);
+            this.SpectralBlocks = Buffer2D<Block8x8>.CreateClean(this.SizeInBlocks);
+
+            if (decoder.ComponentCount > 1 && (this.Index == 1 || this.Index == 2))
+            {
+                Size s0 = decoder.Components[0].SamplingFactors;
+                this.SubSamplingDivisors = s0.DivideBy(this.SamplingFactors);
+            }
         }
 
         /// <summary>
         /// Initializes all component data except <see cref="SpectralBlocks"/>.
         /// </summary>
         /// <param name="decoder">The <see cref="OrigJpegDecoderCore"/> instance</param>
-        public void InitializeData(OrigJpegDecoderCore decoder)
+        public void InitializeCoreData(OrigJpegDecoderCore decoder)
         {
             // Section B.2.2 states that "the value of C_i shall be different from
             // the values of C_1 through C_(i-1)".
@@ -146,8 +152,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
                         case 1:
                             {
                                 // Cb.
-                                if (decoder.Components[0].HorizontalSamplingFactor % h != 0
+
-                                    || decoder.Components[0].VerticalSamplingFactor % v != 0)
+                                Size s0 = decoder.Components[0].SamplingFactors;
+
+                                if (s0.Width % h != 0 || s0.Height % v != 0)
                                 {
                                     throw new ImageFormatException("Unsupported subsampling ratio");
                                 }
@@ -158,8 +166,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
                         case 2:
                             {
                                 // Cr.
-                                if (decoder.Components[1].HorizontalSamplingFactor != h
+
-                                    || decoder.Components[1].VerticalSamplingFactor != v)
+                                Size s1 = decoder.Components[1].SamplingFactors;
+
+                                if (s1.Width != h || s1.Height != v)
                                 {
                                     throw new ImageFormatException("Unsupported subsampling ratio");
                                 }
@@ -199,8 +209,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
 
                             break;
                         case 3:
-                            if (decoder.Components[0].HorizontalSamplingFactor != h
+                            Size s0 = decoder.Components[0].SamplingFactors;
-                                || decoder.Components[0].VerticalSamplingFactor != v)
+
+                            if (s0.Width != h || s0.Height != v)
                             {
                                 throw new ImageFormatException("Unsupported subsampling ratio");
                             }
@@ -211,8 +222,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
                     break;
             }
 
-            this.HorizontalSamplingFactor = h;
+            this.SamplingFactors = new Size(h, v);
-            this.VerticalSamplingFactor = v;
         }
 
         public void Dispose()

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

@@ -149,8 +149,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
                     for (int scanIndex = 0; scanIndex < this.componentScanCount; scanIndex++)
                     {
                         this.ComponentIndex = this.pointers.ComponentScan[scanIndex].ComponentIndex;
-                        this.hi = decoder.Components[this.ComponentIndex].HorizontalSamplingFactor;
+                        OrigComponent component = decoder.Components[this.ComponentIndex];
-                        int vi = decoder.Components[this.ComponentIndex].VerticalSamplingFactor;
+
+                        this.hi = component.HorizontalSamplingFactor;
+                        int vi = component.VerticalSamplingFactor;
 
                         for (int j = 0; j < this.hi * vi; j++)
                         {
@@ -172,7 +174,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
                             }
 
                             // Find the block at (bx,by) in the component's buffer:
-                            OrigComponent component = decoder.Components[this.ComponentIndex];
                             ref Block8x8 blockRefOnHeap = ref component.GetBlockReference(this.bx, this.by);
 
                             // Copy block to stack

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

@@ -2,8 +2,10 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Threading.Tasks;
 using SixLabors.ImageSharp.Formats.Jpeg.Common;
@@ -14,13 +16,9 @@ using SixLabors.ImageSharp.MetaData.Profiles.Exif;
 using SixLabors.ImageSharp.MetaData.Profiles.Icc;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.Primitives;
-using Block8x8F = SixLabors.ImageSharp.Formats.Jpeg.Common.Block8x8F;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
 {
-    using System.Collections.Generic;
-    using System.Numerics;
-
     /// <summary>
     /// Performs the jpeg decoding operation.
     /// </summary>
@@ -143,6 +141,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
 
         public Size ImageSizeInBlocks { get; private set; }
 
+        public Size ImageSizeInMCU { get; private set; }
+
         /// <summary>
         /// Gets the number of color components within the image.
         /// </summary>
@@ -178,12 +178,12 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
         /// <summary>
         /// Gets the number of MCU-s (Minimum Coded Units) in the image along the X axis
         /// </summary>
-        public int MCUCountX { get; private set; }
+        public int MCUCountX => this.ImageSizeInMCU.Width;
 
         /// <summary>
         /// Gets the number of MCU-s (Minimum Coded Units) in the image along the Y axis
         /// </summary>
-        public int MCUCountY { get; private set; }
+        public int MCUCountY => this.ImageSizeInMCU.Height;
 
         /// <summary>
         /// Gets the the total number of MCU-s (Minimum Coded Units) in the image.
@@ -1178,7 +1178,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
             int height = (this.Temp[1] << 8) + this.Temp[2];
             int width = (this.Temp[3] << 8) + this.Temp[4];
 
-            this.InitSizes(width, height);
+            this.ImageSizeInPixels = new Size(width, height);
+            
 
             if (this.Temp[5] != this.ComponentCount)
             {
@@ -1191,33 +1192,22 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
             {
                 byte componentIdentifier = this.Temp[6 + (3 * i)];
                 var component = new OrigComponent(componentIdentifier, i);
-                component.InitializeData(this);
+                component.InitializeCoreData(this);
                 this.Components[i] = component;
             }
 
             int h0 = this.Components[0].HorizontalSamplingFactor;
             int v0 = this.Components[0].VerticalSamplingFactor;
-            this.MCUCountX = (this.ImageWidth + (8 * h0) - 1) / (8 * h0);
-            this.MCUCountY = (this.ImageHeight + (8 * v0) - 1) / (8 * v0);
 
-            // As a preparation for parallelizing Scan decoder, we also allocate DecodedBlocks in the non-progressive case!
+            this.ImageSizeInMCU = this.ImageSizeInPixels.GetSubSampledSize(8 * h0, 8 * v0);
-            for (int i = 0; i < this.ComponentCount; i++)
+
+            foreach (OrigComponent component in this.Components)
             {
-               this.Components[i].InitializeBlocks(this);
+                component.InitializeDerivedData(this);
             }
 
+            this.ImageSizeInBlocks = this.Components[0].SizeInBlocks;
             this.SubsampleRatio = ComponentUtils.GetSubsampleRatio(this.Components);
         }
-
-        private void InitSizes(int width, int height)
-        {
-            this.ImageSizeInPixels = new Size(width, height);
-
-            var sizeInBlocks = (Vector2)(SizeF)this.ImageSizeInPixels;
-            sizeInBlocks /= 8;
-            sizeInBlocks.X = MathF.Ceiling(sizeInBlocks.X);
-            sizeInBlocks.Y = MathF.Ceiling(sizeInBlocks.Y);
-            this.ImageSizeInBlocks = new Size((int)sizeInBlocks.X, (int)sizeInBlocks.Y);
-        }
     }
 }

src/ImageSharp/Formats/Jpeg/PdfJsPort/Components/PdfJsFrameComponent.cs

@@ -5,6 +5,7 @@ using System;
 using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp.Formats.Jpeg.Common;
 using SixLabors.ImageSharp.Memory;
+using SixLabors.Primitives;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.PdfJsPort.Components
 {
@@ -35,14 +36,21 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.PdfJsPort.Components
         /// </summary>
         public int Pred { get; set; }
 
-        /// <inheritdoc />
+        /// <summary>
+        /// Gets the horizontal sampling factor.
+        /// </summary>
         public int HorizontalSamplingFactor { get; }
 
-        /// <inheritdoc />
+        /// <summary>
+        /// Gets the vertical sampling factor.
+        /// </summary>
         public int VerticalSamplingFactor { get; }
 
         Buffer2D<Block8x8> IJpegComponent.SpectralBlocks => throw new NotImplementedException();
 
+        // TODO: Should be derived from PdfJsComponent.Scale
+        public Size SubSamplingDivisors => throw new NotImplementedException();
+
         /// <inheritdoc />
         public int QuantizationTableIndex { get; }
 
@@ -54,10 +62,18 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.PdfJsPort.Components
         /// <inheritdoc />
         public int Index { get; }
 
-        /// <inheritdoc />
+        public Size SizeInBlocks => new Size(this.WidthInBlocks, this.HeightInBlocks);
+
+        public Size SamplingFactors => new Size(this.HorizontalSamplingFactor, this.VerticalSamplingFactor);
+
+        /// <summary>
+        /// Gets the number of blocks per line
+        /// </summary>
         public int WidthInBlocks { get; private set; }
 
-        /// <inheritdoc />
+        /// <summary>
+        /// Gets the number of blocks per column
+        /// </summary>
         public int HeightInBlocks { get; private set; }
 
         /// <summary>

src/ImageSharp/Memory/Buffer2D.cs

@@ -62,6 +62,9 @@ namespace SixLabors.ImageSharp.Memory
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
             get
             {
+                DebugGuard.MustBeLessThan(x, this.Width, nameof(x));
+                DebugGuard.MustBeLessThan(y, this.Height, nameof(y));
+
                 return ref this.Array[(this.Width * y) + x];
             }
         }

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

@@ -5,9 +5,7 @@
 namespace SixLabors.ImageSharp.Tests.Formats.Jpg
 {
     using SixLabors.ImageSharp.Formats.Jpeg.Common;
-    using SixLabors.ImageSharp.Formats.Jpeg.GolangPort;
     using SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder;
-    using SixLabors.ImageSharp.Tests.Formats.Jpg.Utils;
     using SixLabors.Primitives;
 
     using Xunit;
@@ -41,6 +39,22 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
             Assert.Equal(new Size(400 / expectedDivX, 400 / expectedDivY), size);
         }
 
+        [Theory]
+        [InlineData(SubsampleRatio.Ratio410, 4, 2)]
+        [InlineData(SubsampleRatio.Ratio411, 4, 1)]
+        [InlineData(SubsampleRatio.Ratio420, 2, 2)]
+        [InlineData(SubsampleRatio.Ratio422, 2, 1)]
+        [InlineData(SubsampleRatio.Ratio440, 1, 2)]
+        [InlineData(SubsampleRatio.Ratio444, 1, 1)]
+        [InlineData(SubsampleRatio.Undefined, 1, 1)]
+        internal void GetChrominanceSubSampling(SubsampleRatio ratio, int expectedDivX, int expectedDivY)
+        {
+            (int divX, int divY) = ratio.GetChrominanceSubSampling();
+
+            Assert.Equal(expectedDivX, divX);
+            Assert.Equal(expectedDivY, divY);
+        }
+
         [Theory]
         [InlineData(SubsampleRatio.Ratio410, 4)]
         [InlineData(SubsampleRatio.Ratio411, 4)]
@@ -68,64 +82,5 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
             this.Output.WriteLine($"{name}: Stride={channel.Stride}");
         }
 
-        [Fact]
-        public void CalculateJpegChannelSizes_Grayscale()
-        {
-            using (OrigJpegDecoderCore decoder = JpegFixture.ParseStream(TestImages.Jpeg.Baseline.Jpeg400))
-            {
-                Size[] sizes = ComponentUtils.CalculateJpegChannelSizes(decoder.Components, decoder.SubsampleRatio);
-
-                Assert.Equal(1, sizes.Length);
-
-                Size expected = decoder.Components[0].SizeInBlocks() * 8;
-
-                Assert.Equal(expected, sizes[0]);
-            }
-        }
-
-        [Theory]
-        [InlineData(TestImages.Jpeg.Baseline.Jpeg444, 1, 1)]
-        [InlineData(TestImages.Jpeg.Baseline.Jpeg420Exif, 2, 2)]
-        [InlineData(TestImages.Jpeg.Baseline.Jpeg420Small, 2, 2)]
-        public void CalculateJpegChannelSizes_YCbCr(
-            string imageFile,
-            int hDiv,
-            int vDiv)
-        {
-            using (OrigJpegDecoderCore decoder = JpegFixture.ParseStream(imageFile))
-            {
-                Size[] s = ComponentUtils.CalculateJpegChannelSizes(decoder.Components, decoder.SubsampleRatio);
-
-                Assert.Equal(3, s.Length);
-
-                Size ySize = decoder.Components[0].SizeInBlocks() * 8;
-                Size cSize = ySize;
-                cSize.Width /= hDiv;
-                cSize.Height /= vDiv;
-
-                Assert.Equal(ySize, s[0]);
-                Assert.Equal(cSize, s[1]);
-                Assert.Equal(cSize, s[2]);
-            }
-        }
-
-        [Theory]
-        [InlineData(TestImages.Jpeg.Baseline.Ycck)]
-        [InlineData(TestImages.Jpeg.Baseline.Cmyk)]
-        public void CalculateJpegChannelSizes_4Chan(string imageFile)
-        {
-            using (OrigJpegDecoderCore decoder = JpegFixture.ParseStream(imageFile))
-            {
-                Size[] sizes = ComponentUtils.CalculateJpegChannelSizes(decoder.Components, decoder.SubsampleRatio);
-                Assert.Equal(4, sizes.Length);
-
-                Size expected = decoder.Components[0].SizeInBlocks() * 8;
-
-                foreach (Size s in sizes)
-                {
-                    Assert.Equal(expected, s);
-                }
-            }
-        }
     }
 }

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

@@ -16,6 +16,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
     using SixLabors.ImageSharp.PixelFormats;
     using SixLabors.ImageSharp.Tests.Formats.Jpg.Utils;
     using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
+    using SixLabors.Primitives;
 
     using Xunit;
     using Xunit.Abstractions;
@@ -68,7 +69,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
         {
             using (OrigJpegDecoderCore decoder = JpegFixture.ParseStream(TestImages.Jpeg.Progressive.Progress))
             {
-                VerifyJpeg.Components3(decoder.Components, 43, 61, 22, 31, 22, 31);
+                VerifyJpeg.VerifyComponentSizes3(decoder.Components, 43, 61, 22, 31, 22, 31);
             }
         }
 
@@ -81,10 +82,10 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
                 var decoder = new PdfJsJpegDecoderCore(Configuration.Default, new JpegDecoder());
                 decoder.ParseStream(ms);
 
-                VerifyJpeg.Components3(decoder.Frame.Components, 43, 61, 22, 31, 22, 31);
+                VerifyJpeg.VerifyComponentSizes3(decoder.Frame.Components, 43, 61, 22, 31, 22, 31);
             }
         }
-
+        
         public const string DecodeBaselineJpegOutputName = "DecodeBaselineJpeg";
 
         [Theory]

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

@@ -55,6 +55,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
 
         [Theory]
         [WithFile(TestImages.Jpeg.Baseline.Calliphora, PixelTypes.Rgba32)]
+        [WithFile(TestImages.Jpeg.Baseline.Jpeg444, PixelTypes.Rgba32)]
         [WithFile(TestImages.Jpeg.Baseline.Testorig420, PixelTypes.Rgba32)]
         public void PostProcess<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : struct, IPixel<TPixel>

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

@@ -40,7 +40,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
             // I knew this one well:
             if (testImage == TestImages.Jpeg.Progressive.Progress)
             {
-                VerifyJpeg.Components3(data.Components, 43, 61, 22, 31, 22, 31);
+                VerifyJpeg.VerifyComponentSizes3(data.Components, 43, 61, 22, 31, 22, 31);
             }
         }
     }

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

@@ -0,0 +1,84 @@
+using SixLabors.ImageSharp.Formats.Jpeg.Common;
+using SixLabors.ImageSharp.Formats.Jpeg.GolangPort;
+using SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder;
+using SixLabors.ImageSharp.Tests.Formats.Jpg.Utils;
+using SixLabors.Primitives;
+using Xunit;
+using Xunit.Abstractions;
+// ReSharper disable InconsistentNaming
+
+namespace SixLabors.ImageSharp.Tests.Formats.Jpg
+{    
+    public class ParseStreamTests
+    {
+        private ITestOutputHelper Output { get; }
+
+        public ParseStreamTests(ITestOutputHelper output)
+        {
+            this.Output = output;
+        }
+
+        [Fact]
+        public void ComponentScalingIsCorrect_1ChannelJpeg()
+        {
+            using (OrigJpegDecoderCore decoder = JpegFixture.ParseStream(TestImages.Jpeg.Baseline.Jpeg400))
+            {
+                Assert.Equal(1, decoder.ComponentCount);
+                Assert.Equal(1, decoder.Components.Length);
+
+                Size sizeInBlocks = decoder.ImageSizeInBlocks;
+
+                Size expectedSizeInBlocks = decoder.ImageSizeInPixels.GetSubSampledSize(8);
+
+                Assert.Equal(expectedSizeInBlocks, sizeInBlocks);
+                Assert.Equal(sizeInBlocks, decoder.ImageSizeInMCU);
+
+                var uniform1 = new Size(1, 1);
+                OrigComponent c0 = decoder.Components[0];
+                VerifyJpeg.VerifyComponent(c0, expectedSizeInBlocks, uniform1, uniform1);
+            }
+        }
+        
+        [Theory]
+        [InlineData(TestImages.Jpeg.Baseline.Jpeg444, 3, 1, 1)]
+        [InlineData(TestImages.Jpeg.Baseline.Jpeg420Exif, 3, 2, 2)]
+        [InlineData(TestImages.Jpeg.Baseline.Jpeg420Small, 3, 2, 2)]
+        [InlineData(TestImages.Jpeg.Baseline.Ycck, 4, 1, 1)]  // TODO: Find Ycck or Cmyk images with different subsampling
+        [InlineData(TestImages.Jpeg.Baseline.Cmyk, 4, 1, 1)]
+        public void ComponentScalingIsCorrect_MultiChannelJpeg(
+            string imageFile,
+            int componentCount,
+            int hDiv,
+            int vDiv)
+        {
+            Size divisor = new Size(hDiv, vDiv);
+
+            using (OrigJpegDecoderCore decoder = JpegFixture.ParseStream(imageFile))
+            {
+                Assert.Equal(componentCount, decoder.ComponentCount);
+                Assert.Equal(componentCount, decoder.Components.Length);
+                
+                OrigComponent c0 = decoder.Components[0];
+                OrigComponent c1 = decoder.Components[1];
+                OrigComponent c2 = decoder.Components[2];
+
+                var uniform1 = new Size(1, 1);
+                Size expectedLumaSizeInBlocks = decoder.ImageSizeInPixels.GetSubSampledSize(8);
+                Size expectedChromaSizeInBlocks = expectedLumaSizeInBlocks.DivideBy(divisor);
+
+                Size expectedLumaSamplingFactors = expectedLumaSizeInBlocks.DivideBy(decoder.ImageSizeInMCU);
+                Size expectedChromaSamplingFactors = expectedLumaSamplingFactors.DivideBy(divisor);
+
+                VerifyJpeg.VerifyComponent(c0, expectedLumaSizeInBlocks, expectedLumaSamplingFactors, uniform1);
+                VerifyJpeg.VerifyComponent(c1, expectedChromaSizeInBlocks, expectedChromaSamplingFactors, divisor);
+                VerifyJpeg.VerifyComponent(c2, expectedChromaSizeInBlocks, expectedChromaSamplingFactors, divisor);
+
+                if (componentCount == 4)
+                {
+                    OrigComponent c3 = decoder.Components[2];
+                    VerifyJpeg.VerifyComponent(c3, expectedLumaSizeInBlocks, expectedLumaSamplingFactors, uniform1);
+                }
+            }
+        }
+    }
+}

tests/ImageSharp.Tests/Formats/Jpg/Utils/LibJpegTools.ComponentData.cs

@@ -26,14 +26,16 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg.Utils
 
             public int Index { get; }
 
-            public int HeightInBlocks { get; }
+            public Size SizeInBlocks => new Size(this.WidthInBlocks, this.HeightInBlocks);
-            
-            public int WidthInBlocks { get; }
 
-            public int HorizontalSamplingFactor => throw new NotSupportedException();
+            public Size SamplingFactors => throw new NotSupportedException();
 
-            public int VerticalSamplingFactor => throw new NotSupportedException();
+            public Size SubSamplingDivisors => throw new NotSupportedException();
 
+            public int HeightInBlocks { get; }
+            
+            public int WidthInBlocks { get; }
+            
             public int QuantizationTableIndex => throw new NotSupportedException();
 
             public Buffer2D<Block8x8> SpectralBlocks { get; private set; }
@@ -72,8 +74,8 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg.Utils
             public static ComponentData Load(OrigComponent c)
             {
                 var result = new ComponentData(
-                    c.HeightInBlocks,
+                    c.SizeInBlocks.Width,
-                    c.WidthInBlocks,
+                    c.SizeInBlocks.Height,
                     c.Index
                 );
 

tests/ImageSharp.Tests/Formats/Jpg/Utils/VerifyJpeg.cs

@@ -5,19 +5,30 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg.Utils
 
     using SixLabors.ImageSharp.Formats.Jpeg.Common;
     using SixLabors.ImageSharp.PixelFormats;
+    using SixLabors.Primitives;
 
     using Xunit;
     using Xunit.Abstractions;
 
     internal static class VerifyJpeg
     {
-        internal static void ComponentSize(IJpegComponent component, int expectedBlocksX, int expectedBlocksY)
+        internal static void VerifySize(IJpegComponent component, int expectedBlocksX, int expectedBlocksY)
         {
-            Assert.Equal(component.WidthInBlocks, expectedBlocksX);
+            Assert.Equal(new Size(expectedBlocksX, expectedBlocksY), component.SizeInBlocks);
-            Assert.Equal(component.HeightInBlocks, expectedBlocksY);
         }
 
-        internal static void Components3(
+        internal static void VerifyComponent(
+            IJpegComponent component,
+            Size expectedSizeInBlocks,
+            Size expectedSamplingFactors,
+            Size expectedSubsamplingDivisors)
+        {
+            Assert.Equal(expectedSizeInBlocks, component.SizeInBlocks);
+            Assert.Equal(expectedSamplingFactors, component.SamplingFactors);
+            Assert.Equal(expectedSubsamplingDivisors, component.SubSamplingDivisors);
+        }
+        
+        internal static void VerifyComponentSizes3(
             IEnumerable<IJpegComponent> components,
             int xBc0, int yBc0,
             int xBc1, int yBc1,
@@ -26,9 +37,9 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg.Utils
             IJpegComponent[] c = components.ToArray();
             Assert.Equal(3, components.Count());
 
-            ComponentSize(c[0], xBc0, yBc0);
+            VerifySize(c[0], xBc0, yBc0);
-            ComponentSize(c[1], xBc1, yBc1);
+            VerifySize(c[1], xBc1, yBc1);
-            ComponentSize(c[2], xBc2, yBc2);
+            VerifySize(c[2], xBc2, yBc2);
         }
 
         internal static void SaveSpectralImage<TPixel>(TestImageProvider<TPixel> provider, LibJpegTools.SpectralData data, ITestOutputHelper output = null)