Colormap.cs

// Author: Tomáš Karella

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;



namespace _051colormap
{
  class Colormap
  {
      struct Vector3
      {
          public float X;
          public float Y;
          public float Z;

          public static double DistanceSquared(Vector3 a, Vector3 b)
          {
              return  (Math.Pow(a.X - b.X, 2) + Math.Pow(a.Y - b.Y,2) + Math.Pow(a.Z - b.Z,2));
          }

          public static double Distance(Vector3 a, Vector3 b)
          {
              return Math.Sqrt(DistanceSquared(a,b));
          }
      }
        class KeyValueComparer : Comparer<KeyValuePair<Color,long>>
        {
            public override int Compare(KeyValuePair<Color, long> x, KeyValuePair<Color, long> y)
            {
                if (x.Value == y.Value) return 0; 
                else if (x.Value > y.Value) return -1;
                else return 1;
            }
        }
        class PairComparer:IComparer<Pair>
        {
            public int Compare(Pair x, Pair y)
            {
                if (x.value == y.value) return 0;
                else if (x.value > y.value) return -1;
                else return 1;
            }
        }

      class Pair
        {
            public Color color;
            public long value;

          public Pair(Color c, long v)
          {
              color = c;
              value = v;
          }
        }


        /// <summary>
        /// Generate a colormap based on input image.
        /// </summary>
        /// <param name="input">Input raster image.</param>
        /// <param name="numCol">Required colormap size (ignore it if you must)</param>
        /// <param name="colors">Output palette (array of colors).</param>
        /// <param name="colors">Output palette (array of colors).f</param>
        public static void Generate(Bitmap input, int numCol, out Color[] colors)
        {
            int width = input.Width;
            int height = input.Height;
            colors = new Color[numCol];
            Dictionary<Color, long> dic = new Dictionary<Color, long>();
            //hard loop every color,
            for (int i = 0; i < height; i++)
            {
                for (int j = 0; j < width; j++)
                {
                    
                    var c = input.GetPixel(j, i);
                    
                    var cl = Color.FromArgb((c.R/16)*16, (c.G/16)*16, (c.B/16)*16);
                    
                    if (dic.ContainsKey(cl))
                        checked {dic[cl]++;}
                    else dic.Add(cl, 1);
                }
            }
            var l = dic.ToList();
            l.Sort(new KeyValueComparer());
            var myList = new List<Pair>(l.Count);
            foreach (var item in l)
            {
                myList.Add(new Pair(item.Key,item.Value));
            }
            int index = 0;
            while (index < myList.Count)
            {
                var selectItem = myList[index];
                Vector3 v = new Vector3() {X = selectItem.color.R, Y = selectItem.color.G, Z = selectItem.color.B};
                var nList = new List<Pair>();

                for (int i = 0; i <= index;i++)
                {
                    nList.Add(myList[i]);
                }

                for (int i = index+1; i < myList.Count; i++)
                {
                    Vector3 c = new Vector3() {X = myList[i].color.R, Y = myList[i].color.G, Z = myList[i].color.B};
                    if (Vector3.DistanceSquared(v, c) < 5000)
                    {
                        checked
                        {
                            nList[index].value += myList[i].value;
                        }
                    }
                    else nList.Add(new Pair(myList[i].color,myList[i].value));
                }

                index++;
                myList = nList; 
                
            }

            myList.Sort(new PairComparer());
            for (int i = 0; i < numCol; i++)
            {
                if (myList.Count <= i)
                {
                    colors[i] = Color.Black;
                }
                else
                {
                    colors[i] = myList[i].color;
                }
            }
        }
  }
}