/*
 * Greenshot - a free and open source screenshot tool
 * Copyright (C) 2007-2012  Thomas Braun, Jens Klingen, Robin Krom
 * 
 * For more information see: http://getgreenshot.org/
 * The Greenshot project is hosted on Sourceforge: http://sourceforge.net/projects/greenshot/
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 1 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
using System;
using System.Collections;
using System.Drawing;
using System.Drawing.Imaging;
using System.Collections.Generic;

namespace GreenshotPlugin.Core {
	/// <summary>
	/// This interface provides a color quantization capabilities.
	/// </summary>
	public interface IColorQuantizer {
		/// <summary>
		/// Prepares the quantizer for image processing.
		/// </summary>
		/// <param name="image">The image.</param>
		void Prepare(Image image);

		/// <summary>
		/// Adds the color to quantizer.
		/// </summary>
		/// <param name="color">The color to be added.</param>
		void AddColor(Color color);

		/// <summary>
		/// Gets the palette with specified count of the colors.
		/// </summary>
		/// <param name="colorCount">The color count.</param>
		/// <returns></returns>
		List<Color> GetPalette(Int32 colorCount);

		/// <summary>
		/// Gets the index of the palette for specific color.
		/// </summary>
		/// <param name="color">The color.</param>
		/// <returns></returns>
		Int32 GetPaletteIndex(Color color);

		/// <summary>
		/// Gets the color count.
		/// </summary>
		/// <returns></returns>
		Int32 GetColorCount();
	}

	internal class WuColorCube {
		/// <summary>
		/// Gets or sets the red minimum.
		/// </summary>
		/// <value>The red minimum.</value>
		public Int32 RedMinimum { get; set; }

		/// <summary>
		/// Gets or sets the red maximum.
		/// </summary>
		/// <value>The red maximum.</value>
		public Int32 RedMaximum { get; set; }

		/// <summary>
		/// Gets or sets the green minimum.
		/// </summary>
		/// <value>The green minimum.</value>
		public Int32 GreenMinimum { get; set; }

		/// <summary>
		/// Gets or sets the green maximum.
		/// </summary>
		/// <value>The green maximum.</value>
		public Int32 GreenMaximum { get; set; }

		/// <summary>
		/// Gets or sets the blue minimum.
		/// </summary>
		/// <value>The blue minimum.</value>
		public Int32 BlueMinimum { get; set; }

		/// <summary>
		/// Gets or sets the blue maximum.
		/// </summary>
		/// <value>The blue maximum.</value>
		public Int32 BlueMaximum { get; set; }

		/// <summary>
		/// Gets or sets the cube volume.
		/// </summary>
		/// <value>The volume.</value>
		public Int32 Volume { get; set; }
	}

	public class QuantizationHelper {
		private static readonly Color BackgroundColor;
		private static readonly Double[] Factors;

		static QuantizationHelper() {
			BackgroundColor = Color.White;
			Factors = PrecalculateFactors();
		}

		/// <summary>
		/// Precalculates the alpha-fix values for all the possible alpha values (0-255).
		/// </summary>
		private static Double[] PrecalculateFactors() {
			Double[] result = new Double[256];

			for (Int32 value = 0; value < 256; value++) {
				result[value] = value / 255.0;
			}

			return result;
		}

		/// <summary>
		/// Converts the alpha blended color to a non-alpha blended color.
		/// </summary>
		/// <param name="color">The alpha blended color (ARGB).</param>
		/// <returns>The non-alpha blended color (RGB).</returns>
		internal static Color ConvertAlpha(Color color) {
			Color result = color;

			if (color.A < 255) {
				// performs a alpha blending (second color is BackgroundColor, by default a Control color)
				Double colorFactor = Factors[color.A];
				Double backgroundFactor = Factors[255 - color.A];
				Int32 red = (Int32)(color.R * colorFactor + BackgroundColor.R * backgroundFactor);
				Int32 green = (Int32)(color.G * colorFactor + BackgroundColor.G * backgroundFactor);
				Int32 blue = (Int32)(color.B * colorFactor + BackgroundColor.B * backgroundFactor);
				Int32 argb = 255 << 24 | red << 16 | green << 8 | blue;
				result = Color.FromArgb(argb);
			}

			return result;
		}
	}
	/// <summary>
	/// Author:	Xiaolin Wu
	/// Dept. of Computer Science
	/// Univ. of Western Ontario
	/// London, Ontario N6A 5B7
	/// wu@csd.uwo.ca
	/// </summary>
	public class WuColorQuantizer : IColorQuantizer {
		#region | Constants |

		private const Int32 MaxColor = 512;
		private const Int32 Red = 2;
		private const Int32 Green = 1;
		private const Int32 Blue = 0;
		private const Int32 SideSize = 33;
		private const Int32 MaxSideIndex = 32;
		private const Int32 MaxVolume = SideSize * SideSize * SideSize;

		#endregion

		#region | Fields |
		BitArray bitArray;

		private Int32[] reds;
		private Int32[] greens;
		private Int32[] blues;
		private Int32[] sums;
		private Int32[] indices;

		private Int64[, ,] weights;
		private Int64[, ,] momentsRed;
		private Int64[, ,] momentsGreen;
		private Int64[, ,] momentsBlue;
		private Single[, ,] moments;

		private Int32[] tag;
		private Int32[] quantizedPixels;
		private Int32[] table;
		private Color[] pixels;

		private Int32 imageSize;
		private Int32 pixelIndex;

		private WuColorCube[] cubes;

		#endregion

		#region | Helper methods |

		/// <summary>
		/// Converts the histogram to a series of moments.
		/// </summary>
		private void CalculateMoments() {
			Int64[] area = new Int64[SideSize];
			Int64[] areaRed = new Int64[SideSize];
			Int64[] areaGreen = new Int64[SideSize];
			Int64[] areaBlue = new Int64[SideSize];
			Single[] area2 = new Single[SideSize];

			for (Int32 redIndex = 1; redIndex <= MaxSideIndex; ++redIndex) {
				for (Int32 index = 0; index <= MaxSideIndex; ++index) {
					area[index] = 0;
					areaRed[index] = 0;
					areaGreen[index] = 0;
					areaBlue[index] = 0;
					area2[index] = 0;
				}

				for (Int32 greenIndex = 1; greenIndex <= MaxSideIndex; ++greenIndex) {
					Int64 line = 0;
					Int64 lineRed = 0;
					Int64 lineGreen = 0;
					Int64 lineBlue = 0;
					Single line2 = 0.0f;

					for (Int32 blueIndex = 1; blueIndex <= MaxSideIndex; ++blueIndex) {
						line += weights[redIndex, greenIndex, blueIndex];
						lineRed += momentsRed[redIndex, greenIndex, blueIndex];
						lineGreen += momentsGreen[redIndex, greenIndex, blueIndex];
						lineBlue += momentsBlue[redIndex, greenIndex, blueIndex];
						line2 += moments[redIndex, greenIndex, blueIndex];

						area[blueIndex] += line;
						areaRed[blueIndex] += lineRed;
						areaGreen[blueIndex] += lineGreen;
						areaBlue[blueIndex] += lineBlue;
						area2[blueIndex] += line2;

						weights[redIndex, greenIndex, blueIndex] = weights[redIndex - 1, greenIndex, blueIndex] + area[blueIndex];
						momentsRed[redIndex, greenIndex, blueIndex] = momentsRed[redIndex - 1, greenIndex, blueIndex] + areaRed[blueIndex];
						momentsGreen[redIndex, greenIndex, blueIndex] = momentsGreen[redIndex - 1, greenIndex, blueIndex] + areaGreen[blueIndex];
						momentsBlue[redIndex, greenIndex, blueIndex] = momentsBlue[redIndex - 1, greenIndex, blueIndex] + areaBlue[blueIndex];
						moments[redIndex, greenIndex, blueIndex] = moments[redIndex - 1, greenIndex, blueIndex] + area2[blueIndex];
					}
				}
			}
		}

		/// <summary>
		/// Computes the volume of the cube in a specific moment.
		/// </summary>
		private static Int64 Volume(WuColorCube cube, Int64[, ,] moment) {
			return moment[cube.RedMaximum, cube.GreenMaximum, cube.BlueMaximum] -
				   moment[cube.RedMaximum, cube.GreenMaximum, cube.BlueMinimum] -
				   moment[cube.RedMaximum, cube.GreenMinimum, cube.BlueMaximum] +
				   moment[cube.RedMaximum, cube.GreenMinimum, cube.BlueMinimum] -
				   moment[cube.RedMinimum, cube.GreenMaximum, cube.BlueMaximum] +
				   moment[cube.RedMinimum, cube.GreenMaximum, cube.BlueMinimum] +
				   moment[cube.RedMinimum, cube.GreenMinimum, cube.BlueMaximum] -
				   moment[cube.RedMinimum, cube.GreenMinimum, cube.BlueMinimum];
		}

		/// <summary>
		/// Computes the volume of the cube in a specific moment. For the floating-point values.
		/// </summary>
		private static Single VolumeFloat(WuColorCube cube, Single[, ,] moment) {
			return moment[cube.RedMaximum, cube.GreenMaximum, cube.BlueMaximum] -
				   moment[cube.RedMaximum, cube.GreenMaximum, cube.BlueMinimum] -
				   moment[cube.RedMaximum, cube.GreenMinimum, cube.BlueMaximum] +
				   moment[cube.RedMaximum, cube.GreenMinimum, cube.BlueMinimum] -
				   moment[cube.RedMinimum, cube.GreenMaximum, cube.BlueMaximum] +
				   moment[cube.RedMinimum, cube.GreenMaximum, cube.BlueMinimum] +
				   moment[cube.RedMinimum, cube.GreenMinimum, cube.BlueMaximum] -
				   moment[cube.RedMinimum, cube.GreenMinimum, cube.BlueMinimum];
		}

		/// <summary>
		/// Splits the cube in given position, and color direction.
		/// </summary>
		private static Int64 Top(WuColorCube cube, Int32 direction, Int32 position, Int64[, ,] moment) {
			switch (direction) {
				case Red:
					return (moment[position, cube.GreenMaximum, cube.BlueMaximum] -
							moment[position, cube.GreenMaximum, cube.BlueMinimum] -
							moment[position, cube.GreenMinimum, cube.BlueMaximum] +
							moment[position, cube.GreenMinimum, cube.BlueMinimum]);

				case Green:
					return (moment[cube.RedMaximum, position, cube.BlueMaximum] -
							moment[cube.RedMaximum, position, cube.BlueMinimum] -
							moment[cube.RedMinimum, position, cube.BlueMaximum] +
							moment[cube.RedMinimum, position, cube.BlueMinimum]);

				case Blue:
					return (moment[cube.RedMaximum, cube.GreenMaximum, position] -
							moment[cube.RedMaximum, cube.GreenMinimum, position] -
							moment[cube.RedMinimum, cube.GreenMaximum, position] +
							moment[cube.RedMinimum, cube.GreenMinimum, position]);

				default:
					return 0;
			}
		}

		/// <summary>
		/// Splits the cube in a given color direction at its minimum.
		/// </summary>
		private static Int64 Bottom(WuColorCube cube, Int32 direction, Int64[, ,] moment) {
			switch (direction) {
				case Red:
					return (-moment[cube.RedMinimum, cube.GreenMaximum, cube.BlueMaximum] +
							 moment[cube.RedMinimum, cube.GreenMaximum, cube.BlueMinimum] +
							 moment[cube.RedMinimum, cube.GreenMinimum, cube.BlueMaximum] -
							 moment[cube.RedMinimum, cube.GreenMinimum, cube.BlueMinimum]);

				case Green:
					return (-moment[cube.RedMaximum, cube.GreenMinimum, cube.BlueMaximum] +
							 moment[cube.RedMaximum, cube.GreenMinimum, cube.BlueMinimum] +
							 moment[cube.RedMinimum, cube.GreenMinimum, cube.BlueMaximum] -
							 moment[cube.RedMinimum, cube.GreenMinimum, cube.BlueMinimum]);

				case Blue:
					return (-moment[cube.RedMaximum, cube.GreenMaximum, cube.BlueMinimum] +
							 moment[cube.RedMaximum, cube.GreenMinimum, cube.BlueMinimum] +
							 moment[cube.RedMinimum, cube.GreenMaximum, cube.BlueMinimum] -
							 moment[cube.RedMinimum, cube.GreenMinimum, cube.BlueMinimum]);
				default:
					return 0;
			}
		}

		/// <summary>
		/// Calculates statistical variance for a given cube.
		/// </summary>
		private Single CalculateVariance(WuColorCube cube) {
			Single volumeRed = Volume(cube, momentsRed);
			Single volumeGreen = Volume(cube, momentsGreen);
			Single volumeBlue = Volume(cube, momentsBlue);
			Single volumeMoment = VolumeFloat(cube, moments);
			Single volumeWeight = Volume(cube, weights);

			Single distance = volumeRed * volumeRed + volumeGreen * volumeGreen + volumeBlue * volumeBlue;

			return volumeMoment - (distance / volumeWeight);
		}

		/// <summary>
		///	Finds the optimal (maximal) position for the cut.
		/// </summary>
		private Single Maximize(WuColorCube cube, Int32 direction, Int32 first, Int32 last, Int32[] cut, Int64 wholeRed, Int64 wholeGreen, Int64 wholeBlue, Int64 wholeWeight) {
			Int64 bottomRed = Bottom(cube, direction, momentsRed);
			Int64 bottomGreen = Bottom(cube, direction, momentsGreen);
			Int64 bottomBlue = Bottom(cube, direction, momentsBlue);
			Int64 bottomWeight = Bottom(cube, direction, weights);

			Single result = 0.0f;
			cut[0] = -1;

			for (Int32 position = first; position < last; ++position) {
				// determines the cube cut at a certain position
				Int64 halfRed = bottomRed + Top(cube, direction, position, momentsRed);
				Int64 halfGreen = bottomGreen + Top(cube, direction, position, momentsGreen);
				Int64 halfBlue = bottomBlue + Top(cube, direction, position, momentsBlue);
				Int64 halfWeight = bottomWeight + Top(cube, direction, position, weights);

				// the cube cannot be cut at bottom (this would lead to empty cube)
				if (halfWeight != 0) {
					Single halfDistance = halfRed * halfRed + halfGreen * halfGreen + halfBlue * halfBlue;
					Single temp = halfDistance / halfWeight;

					halfRed = wholeRed - halfRed;
					halfGreen = wholeGreen - halfGreen;
					halfBlue = wholeBlue - halfBlue;
					halfWeight = wholeWeight - halfWeight;

					if (halfWeight != 0) {
						halfDistance = halfRed * halfRed + halfGreen * halfGreen + halfBlue * halfBlue;
						temp += halfDistance / halfWeight;

						if (temp > result) {
							result = temp;
							cut[0] = position;
						}
					}
				}
			}

			return result;
		}

		/// <summary>
		/// Cuts a cube with another one.
		/// </summary>
		private Boolean Cut(WuColorCube first, WuColorCube second) {
			Int32 direction;

			Int32[] cutRed = { 0 };
			Int32[] cutGreen = { 0 };
			Int32[] cutBlue = { 0 };

			Int64 wholeRed = Volume(first, momentsRed);
			Int64 wholeGreen = Volume(first, momentsGreen);
			Int64 wholeBlue = Volume(first, momentsBlue);
			Int64 wholeWeight = Volume(first, weights);

			Single maxRed = Maximize(first, Red, first.RedMinimum + 1, first.RedMaximum, cutRed, wholeRed, wholeGreen, wholeBlue, wholeWeight);
			Single maxGreen = Maximize(first, Green, first.GreenMinimum + 1, first.GreenMaximum, cutGreen, wholeRed, wholeGreen, wholeBlue, wholeWeight);
			Single maxBlue = Maximize(first, Blue, first.BlueMinimum + 1, first.BlueMaximum, cutBlue, wholeRed, wholeGreen, wholeBlue, wholeWeight);

			if ((maxRed >= maxGreen) && (maxRed >= maxBlue)) {
				direction = Red;

				// cannot split empty cube
				if (cutRed[0] < 0) return false;
			} else {
				if ((maxGreen >= maxRed) && (maxGreen >= maxBlue)) {
					direction = Green;
				} else {
					direction = Blue;
				}
			}

			second.RedMaximum = first.RedMaximum;
			second.GreenMaximum = first.GreenMaximum;
			second.BlueMaximum = first.BlueMaximum;

			// cuts in a certain direction
			switch (direction) {
				case Red:
					second.RedMinimum = first.RedMaximum = cutRed[0];
					second.GreenMinimum = first.GreenMinimum;
					second.BlueMinimum = first.BlueMinimum;
					break;

				case Green:
					second.GreenMinimum = first.GreenMaximum = cutGreen[0];
					second.RedMinimum = first.RedMinimum;
					second.BlueMinimum = first.BlueMinimum;
					break;

				case Blue:
					second.BlueMinimum = first.BlueMaximum = cutBlue[0];
					second.RedMinimum = first.RedMinimum;
					second.GreenMinimum = first.GreenMinimum;
					break;
			}

			// determines the volumes after cut
			first.Volume = (first.RedMaximum - first.RedMinimum) * (first.GreenMaximum - first.GreenMinimum) * (first.BlueMaximum - first.BlueMinimum);
			second.Volume = (second.RedMaximum - second.RedMinimum) * (second.GreenMaximum - second.GreenMinimum) * (second.BlueMaximum - second.BlueMinimum);

			// the cut was successfull
			return true;
		}

		/// <summary>
		/// Marks all the tags with a given label.
		/// </summary>
		private void Mark(WuColorCube cube, Int32 label, Int32[] tag) {
			for (Int32 redIndex = cube.RedMinimum + 1; redIndex <= cube.RedMaximum; ++redIndex) {
				for (Int32 greenIndex = cube.GreenMinimum + 1; greenIndex <= cube.GreenMaximum; ++greenIndex) {
					for (Int32 blueIndex = cube.BlueMinimum + 1; blueIndex <= cube.BlueMaximum; ++blueIndex) {
						tag[(redIndex << 10) + (redIndex << 6) + redIndex + (greenIndex << 5) + greenIndex + blueIndex] = label;
					}
				}
			}
		}

		#endregion

		#region << IColorQuantizer >>

		/// <summary>
		/// See <see cref="IColorQuantizer.Prepare"/> for more details.
		/// </summary>
		public void Prepare(Image image) {
			bitArray = new BitArray((int)Math.Pow(2, 24));
			// creates all the cubes
			cubes = new WuColorCube[MaxColor];

			// initializes all the cubes
			for (Int32 cubeIndex = 0; cubeIndex < MaxColor; cubeIndex++) {
				cubes[cubeIndex] = new WuColorCube();
			}

			// resets the reference minimums
			cubes[0].RedMinimum = 0;
			cubes[0].GreenMinimum = 0;
			cubes[0].BlueMinimum = 0;

			// resets the reference maximums
			cubes[0].RedMaximum = MaxSideIndex;
			cubes[0].GreenMaximum = MaxSideIndex;
			cubes[0].BlueMaximum = MaxSideIndex;

			weights = new Int64[SideSize, SideSize, SideSize];
			momentsRed = new Int64[SideSize, SideSize, SideSize];
			momentsGreen = new Int64[SideSize, SideSize, SideSize];
			momentsBlue = new Int64[SideSize, SideSize, SideSize];
			moments = new Single[SideSize, SideSize, SideSize];

			table = new Int32[256];

			for (Int32 tableIndex = 0; tableIndex < 256; ++tableIndex) {
				table[tableIndex] = tableIndex * tableIndex;
			}

			pixelIndex = 0;
			imageSize = image.Width * image.Height;

			quantizedPixels = new Int32[imageSize];
			pixels = new Color[imageSize];
		}

		/// <summary>
		/// See <see cref="IColorQuantizer.Prepare"/> for more details.
		/// </summary>
		public void AddColor(Color color) {
			color = QuantizationHelper.ConvertAlpha(color);

			// To count the colors
			bitArray.Set(color.ToArgb() & 0x00ffffff, true);

			Int32 indexRed = (color.R >> 3) + 1;
			Int32 indexGreen = (color.G >> 3) + 1;
			Int32 indexBlue = (color.B >> 3) + 1;

			weights[indexRed, indexGreen, indexBlue]++;
			momentsRed[indexRed, indexGreen, indexBlue] += color.R;
			momentsGreen[indexRed, indexGreen, indexBlue] += color.G;
			momentsBlue[indexRed, indexGreen, indexBlue] += color.B;
			moments[indexRed, indexGreen, indexBlue] += table[color.R] + table[color.G] + table[color.B];

			quantizedPixels[pixelIndex] = (indexRed << 10) + (indexRed << 6) + indexRed + (indexGreen << 5) + indexGreen + indexBlue;
			pixels[pixelIndex] = color;
			pixelIndex++;
		}

		/// <summary>
		/// See <see cref="IColorQuantizer.Prepare"/> for more details.
		/// </summary>
		public Int32 GetColorCount() {
			int result = 0;

			for (int i = 0; i < bitArray.Length; i++) {
				if (bitArray.Get(i)) {
					result++;
				}
			}
			return result;
		}

		/// <summary>
		/// See <see cref="IColorQuantizer.Prepare"/> for more details.
		/// </summary>
		public List<Color> GetPalette(int colorCount) {
			// preprocess the colors
			CalculateMoments();

			Int32 next = 0;
			Single[] volumeVariance = new Single[MaxColor];

			// processes the cubes
			for (Int32 cubeIndex = 1; cubeIndex < colorCount; ++cubeIndex) {
				// if cut is possible; make it
				if (Cut(cubes[next], cubes[cubeIndex])) {
					volumeVariance[next] = cubes[next].Volume > 1 ? CalculateVariance(cubes[next]) : 0.0f;
					volumeVariance[cubeIndex] = cubes[cubeIndex].Volume > 1 ? CalculateVariance(cubes[cubeIndex]) : 0.0f;
				} else // the cut was not possible, revert the index
                {
					volumeVariance[next] = 0.0f;
					cubeIndex--;
				}

				next = 0;
				Single temp = volumeVariance[0];

				for (Int32 index = 1; index <= cubeIndex; ++index) {
					if (volumeVariance[index] > temp) {
						temp = volumeVariance[index];
						next = index;
					}
				}

				if (temp <= 0.0) {
					colorCount = cubeIndex + 1;
					break;
				}
			}

			Int32[] lookupRed = new Int32[MaxColor];
			Int32[] lookupGreen = new Int32[MaxColor];
			Int32[] lookupBlue = new Int32[MaxColor];

			tag = new Int32[MaxVolume];

			// precalculates lookup tables
			for (int k = 0; k < colorCount; ++k) {
				Mark(cubes[k], k, tag);

				long weight = Volume(cubes[k], weights);

				if (weight > 0) {
					lookupRed[k] = (int)(Volume(cubes[k], momentsRed) / weight);
					lookupGreen[k] = (int)(Volume(cubes[k], momentsGreen) / weight);
					lookupBlue[k] = (int)(Volume(cubes[k], momentsBlue) / weight);
				} else {
					lookupRed[k] = 0;
					lookupGreen[k] = 0;
					lookupBlue[k] = 0;
				}
			}

			// copies the per pixel tags 
			for (Int32 index = 0; index < imageSize; ++index) {
				quantizedPixels[index] = tag[quantizedPixels[index]];
			}

			reds = new Int32[colorCount + 1];
			greens = new Int32[colorCount + 1];
			blues = new Int32[colorCount + 1];
			sums = new Int32[colorCount + 1];
			indices = new Int32[imageSize];

			// scans and adds colors
			for (Int32 index = 0; index < imageSize; index++) {
				Color color = pixels[index];

				Int32 match = quantizedPixels[index];
				Int32 bestMatch = match;
				Int32 bestDistance = 100000000;

				for (Int32 lookup = 0; lookup < colorCount; lookup++) {
					Int32 foundRed = lookupRed[lookup];
					Int32 foundGreen = lookupGreen[lookup];
					Int32 foundBlue = lookupBlue[lookup];
					Int32 deltaRed = color.R - foundRed;
					Int32 deltaGreen = color.G - foundGreen;
					Int32 deltaBlue = color.B - foundBlue;

					Int32 distance = deltaRed * deltaRed + deltaGreen * deltaGreen + deltaBlue * deltaBlue;

					if (distance < bestDistance) {
						bestDistance = distance;
						bestMatch = lookup;
					}
				}

				reds[bestMatch] += color.R;
				greens[bestMatch] += color.G;
				blues[bestMatch] += color.B;
				sums[bestMatch]++;

				indices[index] = bestMatch;
			}

			List<Color> result = new List<Color>();

			// generates palette
			for (Int32 paletteIndex = 0; paletteIndex < colorCount; paletteIndex++) {
				if (sums[paletteIndex] > 0) {
					reds[paletteIndex] /= sums[paletteIndex];
					greens[paletteIndex] /= sums[paletteIndex];
					blues[paletteIndex] /= sums[paletteIndex];
				}

				Color color = Color.FromArgb(255, reds[paletteIndex], greens[paletteIndex], blues[paletteIndex]);
				result.Add(color);
			}

			pixelIndex = 0;
			return result;
		}

		/// <summary>
		/// See <see cref="IColorQuantizer.Prepare"/> for more details.
		/// </summary>
		public Int32 GetPaletteIndex(Color color) {
			return indices[pixelIndex++];
		}

		#endregion
	}
}