Coverts a .txt file containing binary values to a .png image

binary2png.js

/**
 * Coverts a .txt file containing 
 * binary values to a .png image
 *
 * Usage: node binary2png.js binary.txt
 */
let fs = require('fs');
let PNG = require('pngjs').PNG;

const inputFile = process.argv.slice(2)[0];
getMatrix(inputFile).then(matrix => {
    const dimention = Math.floor(Math.sqrt(matrix.length));
    let png = new PNG({
        width: dimention,
        height: dimention,
        filterType: -1
    });
    let j = 0;
    for (var y = 0; y < png.height; y++) {
        for (var x = 0; x < png.width; x++) {
            var idx = (png.width * y + x) << 2;
            //rgb
            png.data[idx] = matrix[j][0];
            png.data[idx + 1] = matrix[j][1];
            png.data[idx + 2] = matrix[j][2];
            //alpha
            png.data[idx + 3] = 255;
            j++;
        }
    }
    png.pack().pipe(fs.createWriteStream('myCode.png'))
});

const getMatrix = inputFile => {
    return new Promise((resolve, reject) => {
        fs.readFile(inputFile, 'utf8', (err, data) => {
            if (err) reject(err);
            const matrix = getRgbMatrix(data);
            resolve(matrix);
        });
    });
};

const getRgbMatrix = (stringOfBinary) => {
    const data = stringOfBinary.split(' ');
    let matrix = [], rgb = [];
    for (let i = 0; i < data.length; i++) {
        let px = parseInt(data[i], 2);
        if (px > 127) px -= 256;
        rgb.push(px);
        if ((i + 1) % 3 === 0) {
            matrix.push(rgb);
            rgb = [];
        }
    }
    return matrix;
};