Page Comparison

import processing.video.*;
Capture video;

BlobDetector blobDetector;
color blobColor; 

void setup() {
  size(640, 480);

  video = new Capture(this, width, height, 15);
  video.start();
  
  blobDetector = new BlobDetector();
  blobColor = color(255, 0, 0);

  smooth();
}

void draw() {
  if (video.available()) {
    video.read();
  }
  
  video.loadPixels();
  
  // for black and white image
  // video.filter(THRESHOLD,0.1);
  image(video, 0, 0);
  
  blobDetector.findBlob(blobColor, 20); 
  blobDetector.drawBlob();
  blobDetector.drawBoundingBox();
  blobDetector.drawCenterOfMass();
}

void mousePressed() {
  int loc = mouseX + mouseY*video.width;
  blobColor = video.pixels[loc];
}

class BlobDetector {
  int blobPoints[][];
  int blobWeight = 0;
  PVector centerOfMass;

  BlobDetector() {
    blobPoints = new int[width][height];
    centerOfMass = new PVector(0, 0);
  }

  void findBlob(color blobColor, int threshold) {
    blobWeight = 0;

    for (int x = 0; x < width; x ++ ) {
      for (int y = 0; y < height; y ++ ) {
        int loc = x + y*width;
        color currentColor = video.pixels[loc];

        PVector currColorVec = new PVector(red(currentColor), green(currentColor), blue(currentColor));
        PVector trackColorVec = new PVector(red(blobColor), green(blobColor), blue(blobColor));
        float diff = currColorVec.dist(trackColorVec);

        if (diff < threshold) {
          blobPoints[x][y] = 1;
          blobWeight++;
        } else {
          blobPoints[x][y] = 0;
        }
      }
    }
    
    text(blobWeight, 20, 20);
  }

  void drawBlob() {
    if (blobWeight > 200) {
      for (int x = 0; x < width; x ++ ) {
        for (int y = 0; y < height; y ++ ) {
          if (blobPoints[x][y] == 1) {
            strokeWeight(5);
            stroke(255, 0, 0);
            point(x, y);
          }
        }
      }
    }
  }

  void drawBoundingBox() {
    PVector A = new PVector(width, height);
    PVector B = new PVector(0, 0);
    for (int x = 0; x < width; x ++ ) {
      for (int y = 0; y < height; y ++ ) {
        if (blobPoints[x][y] == 1) {
          if (y < A.y)
            A.y = y;
          if (y > B.y)
            B.y = y;
          if (x < A.x)
            A.x = x;
          if (x > B.x)
            B.x = x;
        }
      }
    }

    strokeWeight(1);
    noFill();
    rect(A.x, A.y, B.x-A.x, B.y-A.y);
    text("A "+A.x+","+A.y, A.x, A.y);
    text("B "+B.x+","+B.y, B.x, B.y);
  }

  void drawCenterOfMass() {
    centerOfMass.set(0.0, 0.0, 0.0);

    for (int x = 0; x < width; x ++ ) {
      for (int y = 0; y < height; y ++ ) {
        if (blobPoints[x][y] == 1) {
          centerOfMass.x += x;
          centerOfMass.y += y;
        }
      }
    }
    
    centerOfMass.x /= blobWeight;
    centerOfMass.y /= blobWeight;

    noStroke();
    fill(255);
    ellipse(centerOfMass.x, centerOfMass.y, 10, 10);
  }
}