Processing examples

imageEffect.pde

PImage kitten;

void setup() {
  size(2024, 512);
  kitten = loadImage("kitten.jpg");
  //kitten.filter(GRAY);
  image(kitten, 0, 0);
}

void draw() {
  kitten.loadPixels();
  for (int x = 0; x < kitten.width; x++) {
    for (int y = 0; y < kitten.height; y++) {
      int index = x+ y * kitten.width;
      color pix = kitten.pixels[index];

      float r = red(pix);
      float g = green(pix);
      float b = blue(pix);

      r = round(4* r/ 255) * (255/4);
      g = round(4* g/ 255) * (255/4);
      b = round(4* b/ 255) * (255/4);

      kitten.pixels[index] = color(r, g, b);
    }
  }

  kitten.updatePixels();
  image(kitten,kitten.width, 0);
}