Compare images - perceptual diffing

compareImages.js

import R from 'ramda';
import fs from 'fs';
import { PNG } from 'pngjs';
import pixelmatch from 'pixelmatch';

export const getImages = imagesPaths => {
    return new Promise(resolve => {
        let filesRead = 0;
        let images = [];

        R.forEach(imagePath => {
            const img = fs
                .createReadStream(imagePath)
                .pipe(new PNG())
                .on('parsed', doneReading);

            function doneReading() {
                filesRead += 1;
                images = [...images, img];
                if (filesRead < imagesPaths.length) return;
                resolve(images);
            }
        }, imagesPaths);
    });
};

export const compareImages = R.curry(async (diffPath, imagePath, imagePath2) => {
    const images = await getImages([imagePath, imagePath2]);

    const png1 = images[0];
    const png2 = images[1];

    const diff = new PNG({ width: png1.width, height: png1.height });

    const diffCount = pixelmatch(png1.data, png2.data, diff.data, png1.width, png1.height, {
        threshold: 0.1
    });

    if (diffCount > 0) {
        diffPath && diff.pack().pipe(fs.createWriteStream(diffPath));
        throw Error('Images are not equal');
    }

    return true;
});