How to do contrast stretching of color image?

private void button1_Click(object sender, EventArgs e)
       {

           int[] maxAndMin = GetMaxMin(bmp);
               for (int i = 0; i < w; i++)
               {
                   for (int j = 0; j < h; j++)
                   {

                       red[i, j] = ((red[i, j] - maxAndMin[1]) * 255 / (maxAndMin[0] - maxAndMin[1]));
                       green [i, j] = ((green [i, j] - maxAndMin[1]) * 255 / (maxAndMin[0] - maxAndMin[1]));
                       blue[i, j] = ((blue[i, j] - maxAndMin[1]) * 255 / (maxAndMin[0] - maxAndMin[1]));

                   }
               }

               int[] histored = new int[256];
               int[] histogreen = new int[256];
               int[] histoblue = new int[256];
               histogram(w, h, red, ref histored);
               histogram(w, h, green, ref histogreen);
               histogram(w, h, blue, ref histoblue);