Código processing do básico

blobsizecomparator.java

import hypermedia.video.Blob;
import java.awt.Rectangle;

public class BlobSizeComparator implements java.util.Comparator<Blob> {
    public int compare(Blob a, Blob b) {
        Rectangle boundingA = a.rectangle;
        Rectangle boundingB = b.rectangle;

        double areaA = boundingA.getHeight() * boundingA.getWidth();
        double areaB = boundingB.getHeight() * boundingB.getWidth();

        return (int)Math.round(areaB - areaA);
    }
}

motiondetection.pde

import hypermedia.video.*;
import java.awt.*;

OpenCV opencv;
PFont font;

int h = 640;
int w = 480;

int threshold = 0;

Blob

ArrayList<Blob> filterBlobs(Blob[] blobs, int numberOfBlobs) {
    ArrayList<Blob> sortedBlobs = new ArrayList<Blob>(Arrays.asList(blobs));

    BlobSizeComparator blobSizeComparator = new BlobSizeComparator();
    Collections.sort(sortedBlobs, (Comparator<Blob>)blobSizeComparator);

    for (int i = sortedBlobs.size() - 1; i >= numberOfBlobs; i--){
        sortedBlobs.remove(i);
    }

    return sortedBlobs;
}

void showBlobs(ArrayList<Blob> blobs) {
    noFill();

    for(Blob blob: blobs) {
        Rectangle bounding_rect = blob.rectangle;
        float area = blob.area;
        float circumference = blob.length;
        Point centroid = blob.centroid;
        Point[] points = blob.points;

        // rectangle
        noFill();
        stroke( blob.isHole ? 128 : 64 );
        rect( bounding_rect.x, bounding_rect.y, bounding_rect.width, bounding_rect.height );

        // centroid
        stroke(0,0,255);
        line( centroid.x-5, centroid.y, centroid.x+5, centroid.y );
        line( centroid.x, centroid.y-5, centroid.x, centroid.y+5 );
        noStroke();
        fill(0,0,255);
        text( area,centroid.x+5, centroid.y+5 );


        fill(255,0,255,64);
        stroke(255,0,255);
        if ( points.length>0 ) {
            beginShape();
            for( int j=0; j<points.length; j++ ) {
                vertex( points[j].x, points[j].y );
            }
            endShape(CLOSE);
        }

        noStroke();
        fill(255,0,255);
        text( circumference, centroid.x+5, centroid.y+15 );
    }
}

void showThreshold(int threshold) {
    text("Current threshold: " + threshold, 10, height - 10);
}

void setup() {
    size(h, w);
    opencv = new OpenCV(this);
    opencv.capture(h, w);

    font = loadFont("AndaleMono.vlw");
    textFont(font);
}

void draw() {
    background(0);
    opencv.read();

    //opencv.flip(OpenCV.FLIP_HORIZONTAL);

    opencv.absDiff();
    opencv.blur(OpenCV.BLUR, 50); // Muito blur para evitar blobs de pequenos dedos, p.e.
    opencv.threshold(threshold); // Grayscale

    image(opencv.image(OpenCV.GRAY), 0, 0);
    opencv.remember();

    ArrayList<Blob> blobs = filterBlobs(opencv.blobs( 300, w*h/2, 20, false ), 1);

    showBlobs(blobs);
    showThreshold(threshold);
}

void mouseClicked() {
    if (mouseButton == LEFT){
        threshold += 10;
    } else {
        threshold -= 10;
    }
}

public void stop() {
    opencv.stop();
    super.stop();
}