import processing.video.*;

Capture cam;

PImage bg;
boolean flg_bg = false;

void setup(){
  size(320, 240);

  String[] cameras = Capture.list();

  for(int i=0; i<cameras.length; i++){
    println("[" + i + "] " + cameras[i]);
  }

  cam = new Capture(this, cameras[3]);
  cam.start();
}

void draw(){
  if(cam.available() == true){
    cam.read();
  }

  if(bg == null){
    image(cam, 0, 0);
  }
  else{
    cam.loadPixels();
    bg.loadPixels();
    for(int i=0; i<cam.pixels.length; i++){
      float y1 = 0.299 * red(cam.pixels[i]) + 0.587 * green(cam.pixels[i]) + 0.114 * blue(cam.pixels[i]);
      float y2 = 0.299 * red(bg.pixels[i]) + 0.587 * green(bg.pixels[i]) + 0.114 *  blue(bg.pixels[i]);
      float d = abs(y1 - y2);

      if(d > 30){
        cam.pixels[i] = color(255, 0, 0);
      }
    }
    cam.updatePixels();

    image(cam, 0, 0);
  }

  if(flg_bg){
    bg = get(0, 0, 320, 240);
    flg_bg = false;
  }

}

void mousePressed(){
  flg_bg = true;
}