Pedestrian tracker using HOG Descriptor and opencv4nodejs

pedestrian-tracker.js

// based from https://github.com/justadudewhohacks/opencv4nodejs/tree/master/examples/simpleTracking1.js
// This code is meant to be run on a Raspberry Pi 3 with the picamera.
// NOTE: Before running this code, for OpenCV to detect the camera, you need to run sudo modprobe bcm2835-v4l2
// TODO: Write each detected frame to an image file somewhere, with the timestamp in the name

const cv = require('opencv4nodejs');
const delay = 50;

const hog = new cv.HOGDescriptor();
hog.setSVMDetector(cv.HOGDescriptor.getDefaultPeopleDetector());

// first arg = camera source or path to file name
const grabFrames = (videoFile, delay, onFrame) => {
  const cap = new cv.VideoCapture(videoFile);
  let done = false;
  const intvl = setInterval(() => {
    // flipcodes: 0 = around x, 1 = around y, -1 = around both
    let frame = cap.read().flip(0);
    // loop back to start on end of stream reached
    if (frame.empty) {
      cap.reset();
      frame = cap.read();
    }
    onFrame(frame);

    const key = cv.waitKey(delay);
    done = key !== -1 && key !== 255;

    if (done) {
      clearInterval(intvl);
      console.log('Key pressed, exiting.');
    }
  }, 0);
};

// 0 arg streams from the picamera
grabFrames(0, delay, frame => {
  // setting the max from 300 to 320 will make this work decently.
  // if we make it smaller than 300, the detector won't work.
  // if bigger, the performance greatly suffers.
  const grayImg = frame.resizeToMax(320).bgrToGray();
  const multiScaleResult = hog.detectMultiScale(grayImg);

  if (multiScaleResult.foundLocations && multiScaleResult.foundLocations.length) {
    multiScaleResult.foundLocations.forEach(location => {
      grayImg.drawRectangle(new cv.Point(location.x, location.y),
                            new cv.Point(location.x + location.width, location.y + location.height),
                            new cv.Vec(0, 255, 0), 2); // bgr vector for color, thickness
      });
      console.log(multiScaleResult.foundLocations, multiScaleResult.foundWeights, new Date());
  }
  cv.imshow('hog', grayImg);
});