Clojure OpenCV Detecting Movement

I have been experimenting with OpenCV to use webcam as a control device. I've put together a sample application which uses difference between frames to detect movement and perform collision detection with objects on the screen.

(ns movement-detect
  (:import (javax.swing JFrame JLabel Timer)
           (java.awt.event ActionListener KeyAdapter)
           (java.awt Canvas Image Color BasicStroke)
           (java.awt.image MemoryImageSource)
           ( OpenCV)))

(def frame-rate (int 1000/30))
(def width 640)
(def height 480)
(def circle-radius 100)

(defn create-circle []
  (let [x (rand-int (- width circle-radius))
        y (rand-int (- height circle-radius))]
    {:x x :y y :area (for [y (range y (+ y circle-radius))
                           x (range x (+ x circle-radius))] [x y])}))

Since we will be moving circles around the screen, we begin by defining a circle, x and y represent the upper left corner of the circle, area contains a list of coordinates that circle occupies on the screen.

(defn vision []
  (doto (OpenCV.)
    (.capture width height)))

(defn capture-image [vis]
  (.read vis)
  (let [raw (.pixels vis)] 
    (doto vis
      (.convert OpenCV/GRAY)
      (.blur OpenCV/BLUR 3)
      (.threshold 20)
    {:raw raw :diff (.pixels vis)}))

We capture a frame from the camera, save a copy of the image as raw, calculate the difference between the current image and the previous one, keeping only parts of the image where there is movement, convert it to grey scale and apply blur on it to remove camera noise, after running it through the threshold filter resulting image will contain white where there is movement black everywhere else.

(defn white-pixel-count [circle pixels]
  (reduce (fn[h v]
            (let [x (first v) y (second v)
                  pix (nth pixels (+ x (* y width)))
                  blue (bit-and pix 0x000000ff)]
              (if (= blue 255) (inc h) h))) 0 (:area circle)))

(defn collision? [circle pixels]
  (let [white (white-pixel-count circle pixels)] 
    (cond (zero? white) false
          (> (/ 1 (/ (count (:area circle)) white)) 0.2) true
          :else false)))

Detecting collision works by counting the number of white pixels under the circle, if more than 20% of the pixels under the circle contains white, it indicates movement.

(defn validate-circles [circles pixels]
  (reduce (fn[h c]
            (if (collision? c pixels)
              (conj h (create-circle))
              (conj h c))) [] @circles))

(defn capture-action [vis panel image circles]
  (proxy [ActionListener] []
     (let [capture (capture-image vis)]
       (dosync (ref-set image capture)
               (ref-set circles (validate-circles circles (:diff capture)))))
     (.repaint panel))))

With every tick of the timer, we'll iterate over the circles on the screen, checking for collision, if there is collision replace that circle with a new one and repaint the panel to reflect changes.

This covers the meat of the code, I have skipped some boiler plate code such as setting up OpenCV or building images which I already covered here. If you end up making anything cool with it, please leave a comment with a link. I'd love to see it.

(defn create-image [panel pixels]
  (let [mis (MemoryImageSource. width height pixels 0 width)]
    (.createImage panel mis)))

(defn panel [image circles]
  (let [canvas (Canvas.)] 
    (proxy [JLabel] [] 
       (let [raw (create-image canvas (:raw @image))
             diff (create-image canvas (:diff @image))]
         (.drawImage g raw 0 0 nil)
         (.drawImage g diff width 0 nil))

       (.setColor g Color/red)
       (.setStroke g (BasicStroke. 10))
       (doseq [c @circles]
         (.draw g (java.awt.geom.Ellipse2D$Double. 
                   (:x c) (:y c) circle-radius circle-radius)))))))

(defn key-listener [vis timer]
  (proxy [KeyAdapter] [] 
     (.stop timer)
     (.dispose vis))))

(defn main []
  (let [vis   (vision)
        image (ref (capture-image vis))
        circles (ref (take 5 (repeatedly create-circle)))
        panel (panel image circles)
        timer (Timer. frame-rate (capture-action vis panel image circles))]
    (.start timer)
    (doto (JFrame.)
      (.add panel)
      (.addKeyListener (key-listener vis timer))
      (.setSize (* 2 width) height)