size(400, 400);

PImage myPic = loadImage("jesterdog.jpg");
myPic.loadPixels();

for (int i = 0; i < myPic.pixels.length; i++)
{
  float r = red(myPic.pixels[i]);
  float g = green(myPic.pixels[i]);
  myPic.pixels[i] = color(r, g, 0);
}

myPic.updatePixels();

image(myPic, 0, 0);