PImage fog;
int flip = 0;
int srcw=512;
int srch=346;
int wid=450;
int hi=300;
color c, cprime;

void setup( ) {
  size(srcw, srch);
  fog = loadImage("stegFog.png");
  image(fog,0,0);
 }
 
 void draw( ) {
   if (mousePressed) {
     for (int i=0; i<srcw; i++){
     for(int j=0; j<srch; j++) {
      c = get(i,j);
      if (i<wid && j<hi) {
         cprime=color(64*(int(red(c))%4),
                      64*(int(green(c))%4),
                      64*(int(blue(c))%4));
         set(i,j, cprime);
      } else {
        set(i,j,c);
      }
     }
    } 
   }
 }