let cam;

​

let hist = Array(256).fill(0);

let nmap = Array(256).fill(0);

let norm = 600;

​

function rgb2gray(img) {

  let nimg = img.get(); // alternatively createImage(img.width, img.height)

  nimg.loadPixels();

  for (let i = 0; i < nimg.pixels.length; i += 4) {

    const Y =

      0.3 * nimg.pixels[i] +

      0.59 * nimg.pixels[i + 1] +

      0.11 * nimg.pixels[i + 2];

    nimg.pixels[i] = nimg.pixels[i + 1] = nimg.pixels[i + 2] = Y;

  }

  nimg.updatePixels();

  return nimg;

}

​

function setup() {

  createCanvas(640, 480);

  cam = createCapture(VIDEO);

  cam.size(width / 2, height / 2);

  cam.hide();

  textSize(18);

}

​

function drawhist(h, x) {

  let sum = 0;

  noStroke();

  for (let i = 0; i < h.length; i++) {

    fill(i);

    sum += h[i];

    rect(i + (width / 2) * x, height / 2, 1, h[i] / (norm / 60));

    rect(i + (width / 2) * x, height - sum / norm, 1, sum / norm);

    fill(255, 0, 0);

    rect(i + (width / 2) * x, height - sum / norm, 2, 2);

    fill(0, 255, 0);

    rect(i + (width / 2) * x, height / 2 + h[i] / 10, 2, 2);

  }

}

​

function calchist(img, h) {

  img.loadPixels();

  for (let i = 0; i < h.length; i++) {

    h[i] = 0;

  }

  for (let i = 0; i < img.pixels.length; i += 4) {

    let g = img.pixels[i];

    h[g]++;

  }

}

​

function draw() {

  let frame = rgb2gray(cam);

​

  background(0, 0, 48);

​

  image(frame, 0, 0);

  frame.loadPixels();

​

  calchist(frame, hist);

  drawhist(hist, 0);

​

  let min_u = -1;

  for (let i = 0; i < hist.length; i++) {

    if (hist[i] != 0) {

      min_u = i;

      break;

    }

  }

​

  let max_u = -1;

  for (let i = hist.length - 1; i >= 0; i++) {

    if (hist[i] != 0) {

      max_u = i;

      break;

    }

  }

  let a = -min_u;

  let b = 255 / (max_u - min_u);

​

  let cdf = 0;

  for (let i = 0; i < hist.length; i++) {

    cdf += hist[i];

    nmap[i] = int((255 * cdf) / (frame.pixels.length / 4));

    //nmap[i] = b * (i + a);

  }

​

  for (let i = 0; i < frame.pixels.length; i += 4) {

    let ivalue = frame.pixels[i];

    frame.pixels[i] = nmap[ivalue];

    frame.pixels[i + 1] = nmap[ivalue];

    frame.pixels[i + 2] = nmap[ivalue];

  }

​

  frame.updatePixels();

  calchist(frame, hist);

​

  drawhist(hist, 1);

  image(frame, width / 2, 0);

​

  stroke(255);

  line(width / 2, 0, width / 2, height);

  line(0, height / 2, width, height / 2);

​

  fill(255, 0, 0);

  noStroke();

  text("CDF", width - 45, height - 50);

  text("CDF", width / 2 - 45, height - 50);

​

  fill(0, 255, 0);

  text("PDF", width - 45, height / 2 + 50);

  text("PDF", width / 2 - 45, height / 2 + 50);

}

​