Laser pen is used to draw. Camera on laptop takes video of screen. Program searches for red pixel in video. Program places blue square where it locates the red pixel. This is projected using the projector. 

import processing.video.*;          //imports the library to work in video

Capture cam;                //Access camera

color trackColor;            //global variables: used all over the program.
float threshold = 10;            //+ and - to track color. A specific color might not be avail                                ble at particular time because of light variations
String s ="CLEAR";            

void setup() {                // fixed things in program

  size(1280,960);            //size of frame it is set to 1280,960 to cover display with                                 black.
  String[] cameras = Capture.list();
  printArray(cameras);
  cam = new Capture(this, cameras[3]);
  printArray(cameras);
  //frameRate(30);            // 30 makes it slow
  background(0);            //black background
  cam = new Capture(this, 1280,960);// It is multiple of basic 640, 480 resolution of video availa                                ble
  cam.start();
  trackColor = color(255,100,100);    //r,g,b (pastel red)
}

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Project duration : One Week