Add error diffusion binerization

src/ImageSharp.Processing/Binarization/Dither.cs

@@ -0,0 +1,50 @@
+// <copyright file="Dither.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp
+{
+    using System;
+
+    using ImageSharp.Dithering;
+    using ImageSharp.Processing.Processors;
+
+    /// <summary>
+    /// Extension methods for the <see cref="Image"/> type.
+    /// </summary>
+    public static partial class ImageExtensions
+    {
+        /// <summary>
+        /// Alters the alpha component of the image.
+        /// </summary>
+        /// <typeparam name="TColor">The pixel format.</typeparam>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="diffuser">The diffusion algorithm to apply.</param>
+        /// <param name="threshold">The threshold to apply binarization of the image. Must be between 0 and 1.</param>
+        /// <returns>The <see cref="Image{TColor}"/>.</returns>
+        public static Image<TColor> Dither<TColor>(this Image<TColor> source, IErrorDiffuser diffuser, float threshold)
+            where TColor : struct, IPackedPixel, IEquatable<TColor>
+        {
+            return Dither(source, diffuser, threshold, source.Bounds);
+        }
+
+        /// <summary>
+        /// Alters the alpha component of the image.
+        /// </summary>
+        /// <typeparam name="TColor">The pixel format.</typeparam>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="diffuser">The diffusion algorithm to apply.</param>
+        /// <param name="threshold">The threshold to apply binarization of the image. Must be between 0 and 1.</param>
+        /// <param name="rectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to alter.
+        /// </param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image<TColor> Dither<TColor>(this Image<TColor> source, IErrorDiffuser diffuser, float threshold, Rectangle rectangle)
+            where TColor : struct, IPackedPixel, IEquatable<TColor>
+        {
+            source.ApplyProcessor(new ErrorDiffusionDitherProcessor<TColor>(diffuser, threshold), rectangle);
+            return source;
+        }
+    }
+}

src/ImageSharp.Processing/Processors/Binarization/BinaryThresholdProcessor.cs

@@ -20,28 +20,26 @@ namespace ImageSharp.Processing.Processors
         /// Initializes a new instance of the <see cref="BinaryThresholdProcessor{TColor}"/> class.
         /// </summary>
         /// <param name="threshold">The threshold to split the image. Must be between 0 and 1.</param>
-        /// <exception cref="System.ArgumentException">
-        /// <paramref name="threshold"/> is less than 0 or is greater than 1.
-        /// </exception>
         public BinaryThresholdProcessor(float threshold)
         {
-            // TODO: Check limit.
+            // TODO: Check thresholding limit. Colors should probably have Max/Min/Middle properties.
             Guard.MustBeBetweenOrEqualTo(threshold, 0, 1, nameof(threshold));
-            this.Value = threshold;
+            this.Threshold = threshold;
 
+            // Default to white/black for upper/lower.
             TColor upper = default(TColor);
-            upper.PackFromVector4(Color.White.ToVector4());
+            upper.PackFromBytes(255, 255, 255, 255);
             this.UpperColor = upper;
 
             TColor lower = default(TColor);
-            lower.PackFromVector4(Color.Black.ToVector4());
+            lower.PackFromBytes(0, 0, 0, 255);
             this.LowerColor = lower;
         }
 
         /// <summary>
         /// Gets the threshold value.
         /// </summary>
-        public float Value { get; }
+        public float Threshold { get; }
 
         /// <summary>
         /// Gets or sets the color to use for pixels that are above the threshold.
@@ -62,7 +60,7 @@ namespace ImageSharp.Processing.Processors
         /// <inheritdoc/>
         protected override void OnApply(ImageBase<TColor> source, Rectangle sourceRectangle)
         {
-            float threshold = this.Value;
+            float threshold = this.Threshold;
             TColor upper = this.UpperColor;
             TColor lower = this.LowerColor;
 

src/ImageSharp.Processing/Processors/Binarization/ErrorDiffusionDitherProcessor.cs

@@ -0,0 +1,111 @@
+// <copyright file="ErrorDiffusionDitherProcessor.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp.Processing.Processors
+{
+    using System;
+
+    using ImageSharp.Dithering;
+
+    /// <summary>
+    /// An <see cref="IImageProcessor{TColor}"/> that dithers an image using error diffusion.
+    /// </summary>
+    /// <typeparam name="TColor">The pixel format.</typeparam>
+    public class ErrorDiffusionDitherProcessor<TColor> : ImageProcessor<TColor>
+        where TColor : struct, IPackedPixel, IEquatable<TColor>
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ErrorDiffusionDitherProcessor{TColor}"/> class.
+        /// </summary>
+        /// <param name="diffuser">The error diffuser</param>
+        /// <param name="threshold">The threshold to split the image. Must be between 0 and 1.</param>
+        public ErrorDiffusionDitherProcessor(IErrorDiffuser diffuser, float threshold)
+        {
+            Guard.NotNull(diffuser, nameof(diffuser));
+
+            // TODO: Check thresholding limit. Colors should probably have Max/Min/Middle properties.
+            Guard.MustBeBetweenOrEqualTo(threshold, 0, 1, nameof(threshold));
+
+            this.Diffuser = diffuser;
+            this.Threshold = threshold;
+
+            // Default to white/black for upper/lower.
+            TColor upper = default(TColor);
+            upper.PackFromBytes(255, 255, 255, 255);
+            this.UpperColor = upper;
+
+            TColor lower = default(TColor);
+            lower.PackFromBytes(0, 0, 0, 255);
+            this.LowerColor = lower;
+        }
+
+        /// <summary>
+        /// Gets the error diffuser.
+        /// </summary>
+        public IErrorDiffuser Diffuser { get; }
+
+        /// <summary>
+        /// Gets the threshold value.
+        /// </summary>
+        public float Threshold { get; }
+
+        /// <summary>
+        /// Gets or sets the color to use for pixels that are above the threshold.
+        /// </summary>
+        public TColor UpperColor { get; set; }
+
+        /// <summary>
+        /// Gets or sets the color to use for pixels that fall below the threshold.
+        /// </summary>
+        public TColor LowerColor { get; set; }
+
+        /// <inheritdoc/>
+        protected override void BeforeApply(ImageBase<TColor> source, Rectangle sourceRectangle)
+        {
+            new GrayscaleBt709Processor<TColor>().Apply(source, sourceRectangle);
+        }
+
+        /// <inheritdoc/>
+        protected override void OnApply(ImageBase<TColor> source, Rectangle sourceRectangle)
+        {
+            int startY = sourceRectangle.Y;
+            int endY = sourceRectangle.Bottom;
+            int startX = sourceRectangle.X;
+            int endX = sourceRectangle.Right;
+
+            // Align start/end positions.
+            int minX = Math.Max(0, startX);
+            int maxX = Math.Min(source.Width, endX);
+            int minY = Math.Max(0, startY);
+            int maxY = Math.Min(source.Height, endY);
+
+            // Reset offset if necessary.
+            if (minX > 0)
+            {
+                startX = 0;
+            }
+
+            if (minY > 0)
+            {
+                startY = 0;
+            }
+
+            using (PixelAccessor<TColor> sourcePixels = source.Lock())
+            {
+                for (int y = minY; y < maxY; y++)
+                {
+                    int offsetY = y - startY;
+                    for (int x = minX; x < maxX; x++)
+                    {
+                        int offsetX = x - startX;
+                        TColor sourceColor = sourcePixels[offsetX, offsetY];
+                        TColor transformedColor = sourceColor.ToVector4().X >= this.Threshold ? this.UpperColor : this.LowerColor;
+                        this.Diffuser.Dither(sourcePixels, sourceColor, transformedColor, offsetX, offsetY, maxX, maxY);
+                    }
+                }
+            }
+        }
+    }
+}

tests/ImageSharp.Tests/Formats/GeneralFormatTests.cs

@@ -111,26 +111,27 @@ namespace ImageSharp.Tests
 
             foreach (TestFile file in Files)
             {
-                Image image = file.CreateImage();
-
-                using (FileStream output = File.OpenWrite($"{path}/{file.FileNameWithoutExtension}.gif"))
+                using (Image image = file.CreateImage())
                 {
-                    image.SaveAsGif(output);
-                }
+                    using (FileStream output = File.OpenWrite($"{path}/{file.FileNameWithoutExtension}.bmp"))
+                    {
+                        image.SaveAsBmp(output);
+                    }
 
-                using (FileStream output = File.OpenWrite($"{path}/{file.FileNameWithoutExtension}.bmp"))
-                {
-                    image.SaveAsBmp(output);
-                }
+                    using (FileStream output = File.OpenWrite($"{path}/{file.FileNameWithoutExtension}.jpg"))
+                    {
+                        image.SaveAsJpeg(output);
+                    }
 
-                using (FileStream output = File.OpenWrite($"{path}/{file.FileNameWithoutExtension}.jpg"))
-                {
-                    image.SaveAsJpeg(output);
-                }
+                    using (FileStream output = File.OpenWrite($"{path}/{file.FileNameWithoutExtension}.png"))
+                    {
+                        image.SaveAsPng(output);
+                    }
 
-                using (FileStream output = File.OpenWrite($"{path}/{file.FileNameWithoutExtension}.png"))
-                {
-                    image.SaveAsPng(output);
+                    using (FileStream output = File.OpenWrite($"{path}/{file.FileNameWithoutExtension}.gif"))
+                    {
+                        image.SaveAsGif(output);
+                    }
                 }
             }
         }
@@ -142,22 +143,25 @@ namespace ImageSharp.Tests
 
             foreach (TestFile file in Files)
             {
-                Image image = file.CreateImage();
-
                 byte[] serialized;
-                using (MemoryStream memoryStream = new MemoryStream())
+                using (Image image = file.CreateImage())
                 {
-                    image.Save(memoryStream);
-                    memoryStream.Flush();
-                    serialized = memoryStream.ToArray();
+                    using (MemoryStream memoryStream = new MemoryStream())
+                    {
+                        image.Save(memoryStream);
+                        memoryStream.Flush();
+                        serialized = memoryStream.ToArray();
+                    }
                 }
 
                 using (MemoryStream memoryStream = new MemoryStream(serialized))
                 {
-                    Image image2 = new Image(memoryStream);
-                    using (FileStream output = File.OpenWrite($"{path}/{file.FileName}"))
+                    using (Image image2 = new Image(memoryStream))
                     {
-                        image2.Save(output);
+                        using (FileStream output = File.OpenWrite($"{path}/{file.FileName}"))
+                        {
+                            image2.Save(output);
+                        }
                     }
                 }
             }

tests/ImageSharp.Tests/Processors/Filters/DitherTest.cs

@@ -0,0 +1,47 @@
+// <copyright file="DitherTest.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp.Tests
+{
+    using System.IO;
+
+    using ImageSharp.Dithering;
+
+    using Xunit;
+
+    public class DitherTest : FileTestBase
+    {
+        [Fact]
+        public void ImageShouldApplyDitherFilter()
+        {
+            string path = this.CreateOutputDirectory("Dither");
+
+            foreach (TestFile file in Files)
+            {
+                using (Image image = file.CreateImage())
+                using (FileStream output = File.OpenWrite($"{path}/{file.FileName}"))
+                {
+                    image.Dither(new SierraLite(), .5F).Save(output);
+                }
+            }
+        }
+
+        [Fact]
+        public void ImageShouldApplyDitherFilterInBox()
+        {
+            string path = this.CreateOutputDirectory("Dither");
+
+            foreach (TestFile file in Files)
+            {
+                string filename = file.GetFileName("-InBox");
+                using (Image image = file.CreateImage())
+                using (FileStream output = File.OpenWrite($"{path}/{filename}"))
+                {
+                    image.Dither(new SierraLite(), .5F, new Rectangle(10, 10, image.Width / 2, image.Height / 2)).Save(output);
+                }
+            }
+        }
+    }
+}