jsPixelEdges

//var img;

​

function preload(){

  img = loadImage("bunker.png");

}

​

function setup(){

  createCanvas(192, 144);

}

​

function draw(){

  background(255);

  //image(img, 0, 0);

  loadPixels(); 

  img.loadPixels();

  for (var x = 0; x < width-1; x++){

    for (var y = 0; y < height-1; y++){

      var loc1 = x     + y*width;

      var loc2 = (x+1) + (y+1)*width;

      var b1 = brightness(img.pixels[loc1]);

      var b2 = brightness(img.pixels[loc2]);

      var diff = abs(b1 - b2);

      pixels[loc1] = color(diff);

    }

  }

  updatePixels();

}