image-diff.js

const fs = require('fs');
const path = require('path');
const PNG = require('pngjs').PNG;
const pixelmatch = require('pixelmatch');

const dir1 = 'dev4';
const dir2 = 'dev5';

fs.readdir(dir1, (err, files) => {
    if (err) throw err;

    files.forEach(file => {
        if (path.extname(file) === '.png') {
            const img1 = PNG.sync.read(fs.readFileSync(path.join(dir1, file)));
            const img2 = PNG.sync.read(fs.readFileSync(path.join(dir2, file)));
            const {width, height} = img1;
            const diff = new PNG({width, height});

            pixelmatch(img1.data, img2.data, diff.data, width, height, {threshold: 0.1});

            diff.pack().pipe(fs.createWriteStream(`diff_${file}`));
        }
    });
});