Convert files to 3-channel JPG using GM

files-converter.js

'use strict'

var fs = require('fs')
  , gm = require('gm');

// transform all files to 3-channel JPG
function convert(dir, out, callback) {
	var i = 0, data = [];
	fs.readdir(dir, function (err, files) {
		if (err) callback(err);

		files.forEach(function (f) {
			gm(dir + f).flatten().setFormat('jpg').colorspace('RGB').write(out + f, function (error) {
				if (!error) data.push(out + f);
			    if (++i === files.length) callback(null, data);
			});
		});
	});
}

convert('./out/', './tmp/', function (err, result) {
	console.log('result', result);
});