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553 lines
20 KiB
553 lines
20 KiB
// <copyright file="OctreeQuantizer.cs" company="James Jackson-South">
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// Copyright (c) James Jackson-South and contributors.
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// Licensed under the Apache License, Version 2.0.
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// </copyright>
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namespace ImageProcessor.Formats
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{
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using System;
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using System.Collections.Generic;
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/// <summary>
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/// Encapsulates methods to calculate the colour palette if an image using an Octree pattern.
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/// <see href="http://msdn.microsoft.com/en-us/library/aa479306.aspx"/>
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/// </summary>
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public class OctreeQuantizer : Quantizer
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{
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/// <summary>
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/// Stores the tree
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/// </summary>
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private readonly Octree octree;
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/// <summary>
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/// Maximum allowed color depth
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/// </summary>
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private readonly int maxColors;
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/// <summary>
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/// The the transparency threshold.
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/// </summary>
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private int threshold = 128;
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/// <summary>
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/// Initializes a new instance of the <see cref="OctreeQuantizer"/> class.
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/// </summary>
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/// <remarks>
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/// The Octree quantizer is a two pass algorithm. The initial pass sets up the Octree,
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/// the second pass quantizes a color based on the nodes in the tree.
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/// <para>
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/// Defaults to return a maximum of 255 colors plus transparency with 8 significant bits.
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/// </para>
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/// </remarks>
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public OctreeQuantizer()
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: this(255, 8)
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{
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}
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/// <summary>
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/// Initializes a new instance of the <see cref="OctreeQuantizer"/> class.
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/// </summary>
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/// <remarks>
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/// The Octree quantizer is a two pass algorithm. The initial pass sets up the Octree,
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/// the second pass quantizes a color based on the nodes in the tree
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/// </remarks>
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/// <param name="maxColors">The maximum number of colors to return</param>
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/// <param name="maxColorBits">The number of significant bits</param>
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public OctreeQuantizer(int maxColors, int maxColorBits)
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: base(false)
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{
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Guard.MustBeLessThanOrEqualTo(maxColors, 255, "maxColors");
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Guard.MustBeBetweenOrEqualTo(maxColorBits, 1, 8, "maxColorBits");
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// Construct the Octree
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this.octree = new Octree(maxColorBits);
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this.maxColors = maxColors;
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}
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/// <summary>
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/// Gets or sets the transparency threshold.
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/// </summary>
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public int Threshold
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{
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get { return this.threshold; }
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set { this.threshold = value.Clamp(0, 255); }
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}
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/// <summary>
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/// Process the pixel in the first pass of the algorithm
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/// </summary>
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/// <param name="pixel">
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/// The pixel to quantize
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/// </param>
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/// <remarks>
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/// This function need only be overridden if your quantize algorithm needs two passes,
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/// such as an Octree quantizer.
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/// </remarks>
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protected override void InitialQuantizePixel(Bgra32 pixel)
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{
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// Add the color to the Octree
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this.octree.AddColor(pixel);
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}
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/// <summary>
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/// Override this to process the pixel in the second pass of the algorithm
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/// </summary>
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/// <param name="pixel">
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/// The pixel to quantize
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/// </param>
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/// <returns>
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/// The quantized value
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/// </returns>
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protected override byte QuantizePixel(Bgra32 pixel)
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{
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// The color at [maxColors] is set to transparent
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byte paletteIndex = (byte)this.maxColors;
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// Get the palette index if it's transparency meets criterea.
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if (pixel.A >= this.Threshold)
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{
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paletteIndex = (byte)this.octree.GetPaletteIndex(pixel);
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}
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return paletteIndex;
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}
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/// <summary>
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/// Retrieve the palette for the quantized image.
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/// </summary>
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/// <returns>
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/// The new color palette
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/// </returns>
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protected override List<Bgra32> GetPalette()
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{
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// First off convert the Octree to maxColors colors
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List<Bgra32> palette = this.octree.Palletize(Math.Max(this.maxColors - 1, 1));
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palette.Add(Bgra32.Empty);
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return palette;
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}
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/// <summary>
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/// Class which does the actual quantization
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/// </summary>
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private class Octree
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{
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/// <summary>
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/// Mask used when getting the appropriate pixels for a given node
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/// </summary>
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private static readonly int[] Mask = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
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/// <summary>
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/// The root of the Octree
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/// </summary>
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private readonly OctreeNode root;
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/// <summary>
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/// Array of reducible nodes
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/// </summary>
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private readonly OctreeNode[] reducibleNodes;
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/// <summary>
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/// Maximum number of significant bits in the image
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/// </summary>
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private readonly int maxColorBits;
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/// <summary>
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/// Number of leaves in the tree
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/// </summary>
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private int leafCount;
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/// <summary>
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/// Store the last node quantized
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/// </summary>
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private OctreeNode previousNode;
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/// <summary>
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/// Cache the previous color quantized
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/// </summary>
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private int previousColor;
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/// <summary>
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/// Initializes a new instance of the <see cref="Octree"/> class.
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/// </summary>
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/// <param name="maxColorBits">
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/// The maximum number of significant bits in the image
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/// </param>
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public Octree(int maxColorBits)
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{
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this.maxColorBits = maxColorBits;
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this.leafCount = 0;
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this.reducibleNodes = new OctreeNode[9];
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this.root = new OctreeNode(0, this.maxColorBits, this);
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this.previousColor = 0;
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this.previousNode = null;
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}
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/// <summary>
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/// Gets or sets the number of leaves in the tree
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/// </summary>
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public int Leaves
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{
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get { return this.leafCount; }
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set { this.leafCount = value; }
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}
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/// <summary>
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/// Gets the array of reducible nodes
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/// </summary>
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private OctreeNode[] ReducibleNodes => this.reducibleNodes;
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/// <summary>
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/// Add a given color value to the Octree
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/// </summary>
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/// <param name="pixel">
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/// The <see cref="Bgra32"/>containing color information to add.
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/// </param>
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public void AddColor(Bgra32 pixel)
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{
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// Check if this request is for the same color as the last
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if (this.previousColor == pixel.Bgra)
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{
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// If so, check if I have a previous node setup. This will only occur if the first color in the image
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// happens to be black, with an alpha component of zero.
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if (this.previousNode == null)
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{
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this.previousColor = pixel.Bgra;
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this.root.AddColor(pixel, this.maxColorBits, 0, this);
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}
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else
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{
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// Just update the previous node
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this.previousNode.Increment(pixel);
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}
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}
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else
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{
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this.previousColor = pixel.Bgra;
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this.root.AddColor(pixel, this.maxColorBits, 0, this);
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}
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}
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/// <summary>
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/// Convert the nodes in the Octree to a palette with a maximum of colorCount colors
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/// </summary>
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/// <param name="colorCount">
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/// The maximum number of colors
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/// </param>
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/// <returns>
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/// An <see cref="List{Bgra}"/> with the palletized colors
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/// </returns>
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public List<Bgra32> Palletize(int colorCount)
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{
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while (this.Leaves > colorCount)
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{
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this.Reduce();
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}
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// Now palletize the nodes
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List<Bgra32> palette = new List<Bgra32>(this.Leaves);
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int paletteIndex = 0;
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this.root.ConstructPalette(palette, ref paletteIndex);
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// And return the palette
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return palette;
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}
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/// <summary>
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/// Get the palette index for the passed color
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/// </summary>
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/// <param name="pixel">
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/// The <see cref="Bgra32"/> containing the pixel data.
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/// </param>
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/// <returns>
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/// The index of the given structure.
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/// </returns>
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public int GetPaletteIndex(Bgra32 pixel)
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{
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return this.root.GetPaletteIndex(pixel, 0);
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}
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/// <summary>
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/// Keep track of the previous node that was quantized
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/// </summary>
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/// <param name="node">
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/// The node last quantized
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/// </param>
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protected void TrackPrevious(OctreeNode node)
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{
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this.previousNode = node;
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}
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/// <summary>
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/// Reduce the depth of the tree
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/// </summary>
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private void Reduce()
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{
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// Find the deepest level containing at least one reducible node
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int index = this.maxColorBits - 1;
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while ((index > 0) && (this.reducibleNodes[index] == null))
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{
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index--;
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}
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// Reduce the node most recently added to the list at level 'index'
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OctreeNode node = this.reducibleNodes[index];
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this.reducibleNodes[index] = node.NextReducible;
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// Decrement the leaf count after reducing the node
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this.leafCount -= node.Reduce();
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// And just in case I've reduced the last color to be added, and the next color to
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// be added is the same, invalidate the previousNode...
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this.previousNode = null;
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}
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/// <summary>
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/// Class which encapsulates each node in the tree
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/// </summary>
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protected class OctreeNode
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{
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/// <summary>
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/// Pointers to any child nodes
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/// </summary>
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private readonly OctreeNode[] children;
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/// <summary>
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/// Flag indicating that this is a leaf node
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/// </summary>
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private bool leaf;
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/// <summary>
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/// Number of pixels in this node
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/// </summary>
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private int pixelCount;
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/// <summary>
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/// Red component
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/// </summary>
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private int red;
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/// <summary>
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/// Green Component
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/// </summary>
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private int green;
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/// <summary>
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/// Blue component
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/// </summary>
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private int blue;
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/// <summary>
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/// The index of this node in the palette
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/// </summary>
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private int paletteIndex;
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/// <summary>
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/// Initializes a new instance of the <see cref="OctreeNode"/> class.
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/// </summary>
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/// <param name="level">
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/// The level in the tree = 0 - 7
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/// </param>
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/// <param name="colorBits">
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/// The number of significant color bits in the image
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/// </param>
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/// <param name="octree">
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/// The tree to which this node belongs
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/// </param>
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public OctreeNode(int level, int colorBits, Octree octree)
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{
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// Construct the new node
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this.leaf = level == colorBits;
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this.red = this.green = this.blue = 0;
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this.pixelCount = 0;
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// If a leaf, increment the leaf count
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if (this.leaf)
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{
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octree.Leaves++;
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this.NextReducible = null;
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this.children = null;
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}
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else
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{
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// Otherwise add this to the reducible nodes
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this.NextReducible = octree.ReducibleNodes[level];
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octree.ReducibleNodes[level] = this;
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this.children = new OctreeNode[8];
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}
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}
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/// <summary>
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/// Gets the next reducible node
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/// </summary>
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public OctreeNode NextReducible { get; }
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/// <summary>
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/// Add a color into the tree
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/// </summary>
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/// <param name="pixel">
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/// The color
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/// </param>
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/// <param name="colorBits">
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/// The number of significant color bits
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/// </param>
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/// <param name="level">
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/// The level in the tree
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/// </param>
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/// <param name="octree">
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/// The tree to which this node belongs
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/// </param>
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public void AddColor(Bgra32 pixel, int colorBits, int level, Octree octree)
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{
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// Update the color information if this is a leaf
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if (this.leaf)
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{
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this.Increment(pixel);
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// Setup the previous node
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octree.TrackPrevious(this);
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}
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else
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{
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// Go to the next level down in the tree
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int shift = 7 - level;
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int index = ((pixel.R & Mask[level]) >> (shift - 2)) |
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((pixel.G & Mask[level]) >> (shift - 1)) |
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((pixel.B & Mask[level]) >> shift);
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OctreeNode child = this.children[index];
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if (child == null)
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{
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// Create a new child node and store it in the array
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child = new OctreeNode(level + 1, colorBits, octree);
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this.children[index] = child;
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}
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// Add the color to the child node
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child.AddColor(pixel, colorBits, level + 1, octree);
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}
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}
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/// <summary>
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/// Reduce this node by removing all of its children
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/// </summary>
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/// <returns>The number of leaves removed</returns>
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public int Reduce()
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{
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this.red = this.green = this.blue = 0;
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int childNodes = 0;
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// Loop through all children and add their information to this node
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for (int index = 0; index < 8; index++)
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{
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if (this.children[index] != null)
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{
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this.red += this.children[index].red;
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this.green += this.children[index].green;
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this.blue += this.children[index].blue;
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this.pixelCount += this.children[index].pixelCount;
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++childNodes;
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this.children[index] = null;
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}
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}
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// Now change this to a leaf node
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this.leaf = true;
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// Return the number of nodes to decrement the leaf count by
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return childNodes - 1;
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}
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/// <summary>
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/// Traverse the tree, building up the color palette
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/// </summary>
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/// <param name="palette">
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/// The palette
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/// </param>
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/// <param name="index">
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/// The current palette index
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/// </param>
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public void ConstructPalette(List<Bgra32> palette, ref int index)
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{
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if (this.leaf)
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{
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// Consume the next palette index
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this.paletteIndex = index++;
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byte r = (this.red / this.pixelCount).ToByte();
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byte g = (this.green / this.pixelCount).ToByte();
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byte b = (this.blue / this.pixelCount).ToByte();
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// And set the color of the palette entry
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palette.Add(new Bgra32(b, g, r));
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}
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else
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{
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// Loop through children looking for leaves
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for (int i = 0; i < 8; i++)
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{
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if (this.children[i] != null)
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{
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this.children[i].ConstructPalette(palette, ref index);
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}
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}
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}
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}
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/// <summary>
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/// Return the palette index for the passed color
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/// </summary>
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/// <param name="pixel">
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/// The <see cref="Bgra32"/> representing the pixel.
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/// </param>
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/// <param name="level">
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/// The level.
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/// </param>
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/// <returns>
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/// The <see cref="int"/> representing the index of the pixel in the palette.
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/// </returns>
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public int GetPaletteIndex(Bgra32 pixel, int level)
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{
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int index = this.paletteIndex;
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if (!this.leaf)
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{
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int shift = 7 - level;
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int pixelIndex = ((pixel.R & Mask[level]) >> (shift - 2)) |
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((pixel.G & Mask[level]) >> (shift - 1)) |
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((pixel.B & Mask[level]) >> shift);
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if (this.children[pixelIndex] != null)
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{
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index = this.children[pixelIndex].GetPaletteIndex(pixel, level + 1);
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}
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else
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{
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throw new Exception("Didn't expect this!");
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}
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}
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return index;
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}
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/// <summary>
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/// Increment the pixel count and add to the color information
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/// </summary>
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/// <param name="pixel">
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/// The pixel to add.
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/// </param>
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public void Increment(Bgra32 pixel)
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{
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this.pixelCount++;
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this.red += pixel.R;
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this.green += pixel.G;
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this.blue += pixel.B;
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}
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}
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}
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}
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}
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