import processing.video.*;
  
  int numPixels;
  int[] backgroundPixels;
  Capture video;
  
  void setup() {
    // Change size to 320 x 240 if too slow at 640 x 480
    size(640, 480); 
    
    video = new Capture(this, width, height, 24);
    numPixels = video.width * video.height;
    // Create array to store the background image
    backgroundPixels = new int[numPixels];
    // Make the pixels[] array available for direct manipulation
    loadPixels();
  }
  
  void draw() {
    if (video.available()) {
      video.read(); // Read a new video frame
      video.loadPixels(); // Make the pixels of video available
      // Difference between the current frame and the stored background
      int presenceSum = 0;
      for (int i = 0; i < numPixels; i++) { // For each pixel in the video frame...
        // Fetch the current color in that location, and also the color
        // of the background in that spot
        color currColor = video.pixels[i];
        color bkgdColor = backgroundPixels[i];
        // Extract the red, green, and blue components of the current pixelÕs color
        int currR = (currColor >> 16) & 0xFF;
        int currG = (currColor >> 8) & 0xFF;
        int currB = currColor & 0xFF;
        // Extract the red, green, and blue components of the background pixelÕs color
        int bkgdR = (bkgdColor >> 16) & 0xFF;
        int bkgdG = (bkgdColor >> 8) & 0xFF;
        int bkgdB = bkgdColor & 0xFF;
        // Compute the difference of the red, green, and blue values
        int diffR = abs(currR - bkgdR);
        int diffG = abs(currG - bkgdG);
        int diffB = abs(currB - bkgdB);
        // Add these differences to the running tally
        presenceSum += diffR + diffG + diffB;
        // Render the difference image to the screen
        pixels[i] = color(diffR, diffG, diffB);
        // The following line does the same thing much faster, but is more technical
        //pixels[i] = 0xFF000000 | (diffR << 16) | (diffG << 8) | diffB;
      }
      updatePixels(); // Notify that the pixels[] array has changed
      println(presenceSum); // Print out the total amount of movement
    }
  }
  
  // When a key is pressed, capture the background image into the backgroundPixels
  // buffer, by copying each of the current frameÕs pixels into it.
  void keyPressed() {
    video.loadPixels();
    arraycopy(video.pixels, backgroundPixels);
  }