Dithering code example

dithering.pde

PImage img; 

int x_max = 0, y_max = 0, _x_max = 0, _y_max = 0 ;
final int inc = 10;

final int color_num = 4;
final float e[] = {7.0/16.0, 3.0/16.0, 5.0/16.0, 1.0/16.0};

void setup()
{
  img =  loadImage("yourimagehere.jpg");
   size( 1920, 1080);
  image(img, 0, 0);
  colorMode(RGB, 255);
  //print(e);
}

void draw()
{
  image(img, 0, 0);
  loadPixels();

  /*Color reduction code*/
  for (int x = 1; x < x_max-1; ++x)
  {
    for (int y = 1; y < y_max-1; ++y)
    {
      color t, c = pixels[x+y*width];
      t = color(255*int(color_num*red(c)/255.0)/color_num, 255*int(color_num*green(c)/255.0)/color_num, 255*int(color_num*blue(c)/255.0)/color_num);
      //println("c: \t", red(c), "\t" , green(c), "\t" , blue(c),"\t|| t: \t", red(t), "\t" , green(t), "\t" , blue(t));
      //println("c: ",hex(c)," | t: ", hex(t)); 
      
      pixels[x+y*width] = t;
      
      if (x_max +10 >= width && y_max + 10 >= height)
      {
        //compute error
        int r_err = int(red(c)   - red(t));
        int g_err = int(green(c) - green(t));
        int b_err = int(blue(c)  - blue(t));
        //println("r_err :", r_err, "g_err :", g_err, "b_err :", b_err);

        c = pixels[(x+1)+(y  )*width]; 
        pixels[(x+1)+(y  )*width] = color(red(c)+r_err*e[0], green(c)+g_err*e[0], blue(c)+b_err*e[0]);
        c = pixels[(x-1)+(y+1)*width]; 
        pixels[(x-1)+(y+1)*width] = color(red(c)+r_err*e[1], green(c)+g_err*e[1], blue(c)+b_err*e[1]);
        c = pixels[(x  )+(y+1)*width]; 
        pixels[(x  )+(y+1)*width] = color(red(c)+r_err*e[2], green(c)+g_err*e[2], blue(c)+b_err*e[2]);
        c = pixels[(x+1)+(y+1)*width]; 
        pixels[(x+1)+(y+1)*width] = color(red(c)+r_err*e[3], green(c)+g_err*e[3], blue(c)+b_err*e[3]);
      }
    }
  }
  x_max =  x_max + inc > width ? x_max : x_max+inc;
  y_max =  y_max + inc > height ? y_max : y_max+inc; 

  if (x_max +10 >= width && y_max + 10 >= height)
  {
    _x_max =  _x_max + 1 > width  ? _x_max : _x_max+1;
    _y_max =  _y_max + 1 > height ? _y_max : _y_max+1;
  }
  updatePixels();
}
//println("x_max:",x_max,"y_max:", y_max);