Video webcam motion detection troubles

Processing for Android
6

Here it is.
You have to give the CAMARA permission to run.
You can test it downloading the app APDE on play store. I’ll take just two minutes.

// Thanks to
// Daniel Shiffman
// http://www.learningprocessing.com
// Code for Android / Ketai by noel

import ketai.camera.*;
KetaiCamera cam;

PImage prevFrame;
float threshold = 50;

void setup() {
  size(320, 240);
  cam = new KetaiCamera(this, 320, 240, 31);
  //  cam.setCameraID(1); // If you want the front camara
  cam.start();
  prevFrame = createImage(cam.width, cam.height, RGB);
}


void onCameraPreviewEvent() {
  prevFrame.copy(cam, 0, 0, cam.width, cam.height, 0, 0, cam.width, cam.height);
  prevFrame.updatePixels();
  cam.read();
}


void draw() {
  background(255);

  // You don't need to display it to analyze it!
  image(cam, 0, 0);

  cam.loadPixels();
  prevFrame.loadPixels();

  // Start with a total of 0
  // These are the variables we'll need to find the average X and Y
  float sumX = 0;
  float sumY = 0;
  int motionCount = 0; 

  // Begin loop to walk through every pixel
  for (int x = 0; x < cam.width; x++ ) {
    for (int y = 0; y < cam.height; y++ ) {
      // What is the current color
      color current = cam.pixels[x+y*cam.width];

      // What is the previous color
      color previous = prevFrame.pixels[x+y*cam.width];

      // Step 4, compare colors (previous vs. current)
      float r1 = red(current); 
      float g1 = green(current);
      float b1 = blue(current);
      float r2 = red(previous); 
      float g2 = green(previous);
      float b2 = blue(previous);

      // Motion for an individual pixel is the difference between the previous color and current color.
      float diff = dist(r1, g1, b1, r2, g2, b2);

      // If it's a motion pixel add up the x's and the y's
      if (diff > threshold) {
        sumX += x;
        sumY += y;
        motionCount++;
      }
    }
  }

  // average location is total location divided by the number of motion pixels.
  float avgX = sumX / motionCount; 
  float avgY = sumY / motionCount; 

  // Draw a circle based on average motion
  smooth();
  noStroke();
  fill(255);
  ellipse(avgX, avgY, 16, 16);
  
}