// Learning Processing
  // Daniel Shiffman
  // http://www.learningprocessing.com
  
  // Example 16-13: Simple motion detection
  
  import processing.video.*;
  // Variable for capture device
  Capture video;
  // Previous Frame
  PImage prevFrame;
  // How different must a pixel be to be a "motion" pixel
  float threshold = 50;
  
  void setup() {
    size(320,240);
    video = new Capture(this, width, height, 30);
    // Create an empty image the same size as the video
    prevFrame = createImage(video.width,video.height,RGB);
  }
  
  void draw() {
    
    // Capture video
    if (video.available()) {
      // Save previous frame for motion detection!!
      prevFrame.copy(video,0,0,video.width,video.height,0,0,video.width,video.height); // Before we read the new frame, we always save the previous frame for comparison!
      prevFrame.updatePixels();
      video.read();
    }
    
    loadPixels();
    video.loadPixels();
    prevFrame.loadPixels();
    
    // Begin loop to walk through every pixel
    for (int x = 0; x < video.width; x ++ ) {
      for (int y = 0; y < video.height; y ++ ) {
        
        int loc = x + y*video.width;            // Step 1, what is the 1D pixel location
        color current = video.pixels[loc];      // Step 2, what is the current color
        color previous = prevFrame.pixels[loc]; // Step 3, what is the previous color
        
        // Step 4, compare colors (previous vs. current)
        float r1 = red(current); float g1 = green(current); float b1 = blue(current);
        float r2 = red(previous); float g2 = green(previous); float b2 = blue(previous);
        float diff = dist(r1,g1,b1,r2,g2,b2);
        
        // Step 5, How different are the colors?
        // If the color at that pixel has changed, then there is motion at that pixel.
        if (diff > threshold) { 
          // If motion, display black
          pixels[loc] = color(0);
        } else {
          // If not, display white
          pixels[loc] = color(255);
        }
      }
    }
    updatePixels();
  }