index.js

var globby = require('globby');
var gm = require('gm').subClass({imageMagick: true});
var mkdirp = require('mkdirp');
var async = require('async');
var path = require('path');
var EventEmitter = require('events').EventEmitter;
var util = require('util');

function Resizer(src, target, size) {
	EventEmitter.call(this);
	if ( typeof(size) === 'string' ) {
		var sizes = size.split('x');
		size = {
			width:parseInt(sizes[0]),
			height:parseInt(sizes[1])
		};
	}
	this._src = src;
	this._target = target;
	this._size = size;
}

util.inherits(Resizer, EventEmitter);

Resizer.prototype.resize = function(file, done) {
	var self = this;
	var fileSrc = path.join(this._src, file);
	var fileDest = path.join(this._target, file);
	var folder = path.dirname(fileDest);
	mkdirp(folder, function() {
		self.emit('image', file, self._size.width + 'x' + self._size.height);
    var options = '!';
    gm(fileSrc).resize(self._size.width, self._size.height, options)
               .write(fileDest, done);
	});
}

module.exports = function(src, glob, target, size, done) {
	var resizer = new Resizer(src, target, size);
	globby(glob, {
		cwd: src
	}, function(err, files) {
		async.forEach(files, function(file, nextFile) {
			resizer.resize(file, nextFile);
		}, done);
	});

	return resizer;
};