using PGraphics

Hi there, I have problems with my code. what I want to do is tracking color pixel. I want to capture an image with the only traced color(without background video). so I used PGraphics, but It is so slow that the program can't track color well. I think using PGraphics makes the program slow. is there any advice to make tracking faster?

Here is my code.

import processing.video.*;

Capture video;

color trackColor= color(145,43,54);
float threshold = 25;
PGraphics topLayer;


float distSq(float x1, float y1, float z1, float x2, float y2, float z2) {
  float d = (x2-x1)*(x2-x1) + (y2-y1)*(y2-y1) +(z2-z1)*(z2-z1);
  return d;
}

void setup() {
  frameRate(60);
  size(640, 360);
  String[] cameras = Capture.list();
  printArray(cameras);
  video = new Capture(this, cameras[3]);
  video.start();
  trackColor = color(145,43,54);
  topLayer = createGraphics(width, height, g.getClass().getName());
}

void captureEvent(Capture video) {
  video.read();
}

void draw() {

  video.loadPixels();
  image(video, 0, 0);

  //threshold = map(mouseX, 0, width, 0, 100);
  threshold = 50;

  int avgX = 0;
  int avgY = 0;
  float worldRecord = 0;

  // Begin loop to walk through every pixel
  for (int x = 0; x < video.width; x++ ) {
    for (int y = 0; y < video.height; y++ ) {
      int loc = x + y * video.width;
      // What is current color
      color currentColor = video.pixels[loc];
      float r1 = red(currentColor);
      float g1 = green(currentColor);
      float b1 = blue(currentColor);
      float r2 = red(trackColor);
      float g2 = green(trackColor);
      float b2 = blue(trackColor);
      //
      float d = distSq(r1, g1, b1, r2, g2, b2); 
      if (d < threshold*threshold) {
        worldRecord = d;
        avgX = x;
        avgY = y;
    }
  }
 }
   topLayer.beginDraw();
  topLayer.stroke(trackColor);
  if (worldRecord < threshold*threshold) {
    topLayer.fill(trackColor);
    topLayer.strokeWeight(1);
    topLayer.point(avgX, avgY); ////////////////////////////////////////
  }
  topLayer.endDraw();
    image(topLayer, 0, 0);
}