Ball tracking example with Node JS and OpenCV

BallTracking.js

// Ball tracking example with Node JS and OpenCV
// Before running this script please check de opencv4nodejs installation steps
// Dependencies: https://www.npmjs.com/package/opencv4nodejs
// Inspired by: https://www.pyimagesearch.com/2014/07/21/detecting-circles-images-using-opencv-hough-circles/
// Author Iddar Olivares <https://github.com/iddar> July 2019

const cv = require('opencv4nodejs');

const delay = 1
const devicePort = 0;
const vCap = new cv.VideoCapture(devicePort);

// important values
const method = cv.HOUGH_GRADIENT;
const dp = 2;
const minDist = 50;
const resolution = 280

function onFrame(frame) {
  const bw = frame.cvtColor(cv.COLOR_BGR2GRAY)
  const circles = bw.houghCircles(method, dp, minDist)

  drawBall(bw, circles)
  cv.imshow('frame', bw);
}

function drawBall (dstImg, circles) {
  circles.forEach(({x, y, z}) => {
    const blue = new cv.Vec(255, 0, 0);
    const orange = new cv.Vec(0, 128, 255);
    dstImg.drawCircle(new cv.Point2(x, y), z, { color: blue, thickness: 2 })
    dstImg.drawRectangle(
      new cv.Point(x - 5, y - 5),
      new cv.Point(x + 5, y + 5),
      { color: orange, thickness: 1 }
    );
  })
}

/**
 * runner
 * Call onFrame every frame
 */
const runner = setInterval(() => {
  let frame = vCap.read();
  // loop back to start on end of stream reached
  if (frame.empty) {
    vCap.reset();
    frame = vCap.read();
  }
  
  let resized = frame.resizeToMax(resolution)
  // let ratio = frame.sizes[0] / parseFloat(resized.sizes[0])
  onFrame(resized);
  
  const key = cv.waitKey(delay);
  done = key !== -1 && key !== 255;
  if (done) {
    clearInterval(runner);
    console.log('Key pressed, exiting.');
  }
}, 0);