Implement the interface for the basic quantizer. The resulting image is not correct with this commit but we have a starting point to troubleshoot the quantizer.

Former-commit-id: 9a02fda23c4ee617948798ca10df40f415469291
Former-commit-id: 2a73febf146145751efde9460f3de24086422727
Former-commit-id: 98a3c0689c9d9a7cb6ca0badf9ef4ebec4e36cac

src/ImageProcessor/Formats/Gif/Quantizer/IQuantizer.cs

@@ -20,8 +20,8 @@ namespace ImageProcessor.Formats
         /// </summary>
         /// <param name="imageBase">The image to quantize.</param>
         /// <returns>
-        /// A <see cref="T:byte[]"/> representing a quantized version of the image pixels.
+        /// A <see cref="T:QuantizedImage"/> representing a quantized version of the image pixels.
         /// </returns>
-        byte[] Quantize(ImageBase imageBase);
+        QuantizedImage Quantize(ImageBase imageBase);
     }
 }

src/ImageProcessor/Formats/Gif/Quantizer/QuantizedImage.cs

@@ -0,0 +1,80 @@
+// --------------------------------------------------------------------------------------------------------------------
+// <copyright file="QuantizedImage.cs" company="James South">
+//   Copyright © James South and contributors.
+//   Licensed under the Apache License, Version 2.0.
+// </copyright>
+// <summary>
+//   Provides methods for allowing quantization of images pixels.
+// </summary>
+// --------------------------------------------------------------------------------------------------------------------
+
+namespace ImageProcessor.Formats
+{
+    using System;
+
+    /// <summary>
+    /// Represents a quantized image where the pixels indexed by a color palette.
+    /// </summary>
+    public class QuantizedImage
+    {
+        /// <summary>
+        /// Gets the width of this <see cref="T:QuantizedImage"/>.
+        /// </summary>
+        public int Width { get; }
+
+        /// <summary>
+        /// Gets the height of this <see cref="T:QuantizedImage"/>.
+        /// </summary>
+        public int Height { get; }
+
+        /// <summary>
+        /// Gets the color palette of this <see cref="T:QuantizedImage"/>.
+        /// </summary>
+        public Bgra[] Palette { get; }
+
+        /// <summary>
+        /// Gets the pixels of this <see cref="T:QuantizedImage"/>.
+        /// </summary>
+        public byte[] Pixels { get; }
+
+        /// <summary>
+        /// Initializes a new instance of <see cref="T:QuantizedImage"/>.
+        /// </summary>
+        public QuantizedImage(int width, int height, Bgra[] palette, byte[] pixels)
+        {
+            if (width <= 0) throw new ArgumentOutOfRangeException(nameof(width));
+            if (height <= 0) throw new ArgumentOutOfRangeException(nameof(height));
+            if (palette == null) throw new ArgumentNullException(nameof(palette));
+            if (pixels == null) throw new ArgumentNullException(nameof(pixels));
+            if (pixels.Length != width * height) throw new ArgumentException("Pixel array size must be width * height", nameof(pixels));
+
+            this.Width = width;
+            this.Height = height;
+            this.Palette = palette;
+            this.Pixels = pixels;
+        }
+
+        /// <summary>
+        /// Converts this quantized image to a normal image.
+        /// </summary>
+        /// <returns></returns>
+        public Image ToImage()
+        {
+            Image image = new Image();
+            int pixelCount = Pixels.Length;
+            byte[] bgraPixels = new byte[pixelCount * 4];
+
+            for (int i = 0; i < pixelCount; i++)
+            {
+                Bgra color = Palette[Pixels[i]];
+                bgraPixels[i + 0] = color.B;
+                bgraPixels[i + 1] = color.G;
+                bgraPixels[i + 2] = color.R;
+                bgraPixels[i + 3] = color.A;
+            }
+
+            image.SetPixels(Width, Height, bgraPixels);
+            return image;
+        }
+    }
+}

src/ImageProcessor/Formats/Gif/Quantizer/Quantizer.cs

@@ -11,6 +11,7 @@
 namespace ImageProcessor.Formats
 {
     using System.Collections.Generic;
+    using System.Linq;
 
     /// <summary>
     /// Encapsulates methods to calculate the color palette of an image.
@@ -45,22 +46,25 @@ namespace ImageProcessor.Formats
         /// <returns>
         /// A <see cref="T:byte[]"/> representing a quantized version of the image pixels.
         /// </returns>
-        public byte[] Quantize(ImageBase imageBase)
+        public QuantizedImage Quantize(ImageBase imageBase)
         {
             // Get the size of the source image
             int height = imageBase.Height;
             int width = imageBase.Width;
-            ImageBase copy = new ImageFrame((ImageFrame)imageBase);
 
             // Call the FirstPass function if not a single pass algorithm.
             // For something like an Octree quantizer, this will run through
             // all image pixels, build a data structure, and create a palette.
-            if (!this.singlePass)
+            if (!singlePass)
             {
-                this.FirstPass(copy, width, height);
+                FirstPass(imageBase, width, height);
             }
 
-            throw new System.NotImplementedException();
+            byte[] quantizedPixels = new byte[width * height];
+
+            SecondPass(imageBase, quantizedPixels, width, height);
+
+            return new QuantizedImage(width, height, GetPalette().ToArray(), quantizedPixels);
         }
 
         /// <summary>
@@ -92,18 +96,34 @@ namespace ImageProcessor.Formats
         /// <param name="height">The height in pixels of the image</param>
         protected virtual void SecondPass(ImageBase source, byte[] output, int width, int height)
         {
-            Bgra sourcePixel = source[0, 0];
+            int i = 0;
 
-            // And convert the first pixel, so that I have values going into the loop
+            // Convert the first pixel, so that I have values going into the loop
-            byte pixelValue = this.QuantizePixel(sourcePixel);
+            Bgra previousPixel = source[0, 0];
+            byte pixelValue = QuantizePixel(previousPixel);
 
             output[0] = pixelValue;
 
             for (int y = 0; y < height; y++)
             {
-                // TODO: Translate this from the old method.
+                for (int x = 0; x < width; x++)
-            }
+                {
+                    Bgra sourcePixel = source[x, y];
 
+                    // Check if this is the same as the last pixel. If so use that value
+                    // rather than calculating it again. This is an inexpensive optimization.
+                    if (sourcePixel != previousPixel)
+                    {
+                        // Quantize the pixel
+                        pixelValue = QuantizePixel(sourcePixel);
+
+                        // And setup the previous pointer
+                        previousPixel = sourcePixel;
+                    }
+
+                    output[i++] = pixelValue;
+                }
+            }
         }
 
         /// <summary>

src/ImageProcessor/ImageProcessor.csproj

@@ -52,6 +52,7 @@
     <Compile Include="Formats\Bmp\BmpEncoder.cs" />
     <Compile Include="Formats\Gif\GifDecoderCore.cs" />
     <Compile Include="Formats\Gif\GifEncoder.cs" />
+    <Compile Include="Formats\Gif\Quantizer\QuantizedImage.cs" />
     <Compile Include="Formats\Gif\Quantizer\IQuantizer.cs" />
     <Compile Include="Formats\Gif\Quantizer\OctreeQuantizer.cs" />
     <Compile Include="Formats\Gif\Quantizer\Quantizer.cs" />

tests/ImageProcessor.Tests/Formats/EncoderDecoderTests.cs

@@ -57,5 +57,25 @@
 
             Trace.WriteLine(string.Format("{0} : {1}ms", filename, watch.ElapsedMilliseconds));
         }
+
+        [Theory]
+        [InlineData("../../TestImages/Formats/Bmp/Car.bmp")]
+        public void QuantizedImageShouldPreserveMaximumColorPrecision(string filename)
+        {
+            if (!Directory.Exists("Quantized"))
+            {
+                Directory.CreateDirectory("Quantized");
+            }
+
+            Image image = new Image(File.OpenRead(filename));
+            IQuantizer quantizer = new OctreeQuantizer();
+            QuantizedImage quantizedImage = quantizer.Quantize(image);
+
+            using (FileStream output = File.OpenWrite($"Quantized/{ Path.GetFileName(filename) }"))
+            {
+                IImageEncoder encoder = Image.Encoders.First(e => e.IsSupportedFileExtension(Path.GetExtension(filename)));
+                encoder.Encode(quantizedImage.ToImage(), output);
+            }
+        }
     }
 }