// Learning Processing
  // Daniel Shiffman
  // http://www.learningprocessing.com
  
  // Example 15-12: Pixel neighbor differences (edges)
  
  PImage img;         // Source image
  PImage destination; // Destination image
  
  void setup() {
    size(200,200);
    img = loadImage("sunflower.jpg");
    destination = createImage(img.width, img.height, RGB);
  }
  
  void draw() {
    
    // We are going to look at both image's pixels
    img.loadPixels();
    destination.loadPixels();
    
    // Since we are looking at left neighbors
    // We skip the first column
    for (int x = 1; x < width; x++ ) {
      for (int y = 0; y < height; y++ ) {
        
        // Pixel location and color
        int loc = x + y*img.width;
        color pix = img.pixels[loc];
        
        // Pixel to the left location and color
        int leftLoc = (x - 1) + y*img.width;
        color leftPix = img.pixels[leftLoc];
        
        // New color is difference between pixel and left neighbor
        float diff = abs(brightness(pix) - brightness(leftPix));
        destination.pixels[loc] = color(diff); 
      }
    }
    
    // We changed the pixels in destination
    destination.updatePixels();
    // Display the destination
    image(destination,0,0);
  }