Compare images with each other and return if the files are equal with zero tolerance

files-comparison.js

'use strict'

var gm = require('gm')
  , fs = require('fs')
  , _ = require('lodash')
  , async = require('async');

/**
 * Compare all files from a folder and return the results.
 */
function compare (dir, callback) {
	fs.readdir(dir, function (err, files) {
		if (err) return callback(err);

		var series = [];
		files.forEach(function (f) {
			// compare 'f' to all other files
			var others = _.without(files, f);			
			others.forEach(function (t) {
				series.push(function (callback) {
					gm.compare(dir + f, dir + t, { tolerance: 0.0 }, function (err, isEqual, equality, raw) {
						if (err) callback(err);
						else callback(null, {
							file: f,
							target: t,
							isEqual: isEqual,
							equality: equality,
						});
					});
				});
			});
		});

		async.series(series, function (err, results) {
			// filter the same results
			results = _.filter(results, { isEqual: true }, 'file');
			var out = [];
			results.forEach(function (o) {
				if (!_.find(out,  function(r) {
					return (o.file === r.file && o.target === r.file) || (o.file === r.target && o.target === r.file);
				})) out.push(o);
			});

			callback(null, out);
		});
	});
}

compare('./out/', function (err, res) {
	if (!err) {
		console.log(res);
	}
	else console.log('err', err);
});