Functions to get the color channels of an image

color_channels.pde

PImage img;
PImage redImg;
PImage greenImg;
PImage blueImg;

void setup(){
  size(250*3, 250*2);
  img = loadImage("testImage.png");
  redImg = loadImage("testImage.png");
  greenImg = loadImage("testImage.png");
  blueImg = loadImage("testImage.png");
  
  redImg.loadPixels();
  redImg.pixels = red(redImg);
  redImg.updatePixels();
  
  greenImg.loadPixels();
  greenImg.pixels = green(greenImg);
  greenImg.updatePixels();
  
  blueImg.loadPixels();
  blueImg.pixels = blue(blueImg);
  blueImg.updatePixels();
}

void draw(){
  background(0);
  image(img,250,0, 250, 250);
  image(redImg, 0, 250, 250, 250);
  image(greenImg, 250, 250, 250, 250);
  image(blueImg, 500, 250, 250,250);
}

int[] red(PImage i){
  int[] result = new int[i.width * i.height];
  for(int p = 0; p<(i.width * i.height); p++){
   color c = color(i.pixels[p]);
   result[p] = color(c >> 16 & 0xff);
  }
  return result;
}

int[] green(PImage i){
  int[] result = new int[i.width * i.height];
  for(int p = 0; p<(i.width * i.height); p++){
   color c = color(i.pixels[p]);
   result[p] =    color(c >> 8 & 0xff);
  }
  return result;
}

int[] blue(PImage i){
  int[] result = new int[i.width * i.height];
  for(int p = 0; p<(i.width * i.height); p++){
   color c = color(i.pixels[p]);
   result[p] = color(c & 0xff);
  }
  return result;
}

See the results here: http://www.flickr.com/photos/unavoidablegrain/7935057952/in/photostream