​

let nightsky;

​

const SAMPLE_WIDTH = 100;

const SAMPLE_HEIGHT = 100;

​

const rgb2luma = (r,g,b) => 0.2989 * r + 0.5870 * g + 0.1140 * b;

const rgb2lumahelper = (getres) => rgb2luma(getres[0], getres[1], getres[2]);

​

function preload() {

  nightsky = loadImage('nightsky.png')

}

​

function setup() {

  createCanvas(800, 600);

  noLoop();

}

​

function draw() {

  background(220);

  image(nightsky, 0,0);

}

​

function mousePressed() {

  let avg = 0;

  for (let i = -SAMPLE_WIDTH / 2; i < SAMPLE_WIDTH / 2; i++) {

    for (let j = -SAMPLE_HEIGHT / 2; j < SAMPLE_HEIGHT / 2; j++) {

      avg += rgb2lumahelper(get(mouseX + i, mouseY + j)) / (SAMPLE_WIDTH * SAMPLE_HEIGHT);

    }

  }

  noFill();

  stroke('red');

  rect(mouseX - SAMPLE_WIDTH / 2, mouseY - SAMPLE_HEIGHT / 2, SAMPLE_WIDTH, SAMPLE_HEIGHT);

  console.log(avg);

}