index.js

var fs = require('fs');
var path = require('path');
var execFile = require('child_process').execFile;

var optimage = module.exports = exports = function (options, done){

    var inputFile = options.inputFile;
    var outputFile = options.outputFile;
    var verbose = options.verbose;
    var level = options.level;
    var progressive = options.progressive;
    var binPath= '';
    var args= [];

    outputFile = outputFile || inputFile;

    switch ( path.extname(inputFile) ){

        // 1. Basic optimisation
        // optipng xx.png -out xx2.png
        // optipng xx.png -dir ./img
        // default -o2

        // TODO
        // 2. Removing unnecessary chunks
        // pngcrush -q -rem gAMA -rem alla -rem text image.png image.crushed.png
        // 3. Reducing the colour palette
        // pngnq -f -n 32 -s 3 image.png
        // 4. Re-compressing final image
        // advpng -z -4 image.png
        case '.png':
            binPath = require('optipng-bin').path;
            // OptiPNG can't overwrite without creating a backup file
            // https://sourceforge.net/tracker/?func=detail&aid=3607244&group_id=151404&atid=780913
            if (path.resolve(outputFile) !== path.resolve(inputFile) && fs.existsSync(outputFile)) {
                fs.unlinkSync(outputFile);
            }
            if(options.arg) args = args.concat(options.arg);
            args.push('-strip', 'all', inputFile, "-out", outputFile, '-o', level||2 );
            break;

        // jpegtran [switches] inputfile outputfile
        case '.jpg':
        case '.jpeg':
            binPath = require('jpegtran-bin').path;
            args.push('-copy', 'none', '-optimize');
            if(progressive) args.push('-progressive');
            if(options.arg) args = args.concat(options.arg);
            args.push('-outfile', outputFile, inputFile)
            break;

        // maybe support to do a merge with frames?
        // that means we need an array for inputOutput.
        case '.gif':
            binPath = require('gifsicle').path;
            args.push('-o', outputFile, inputFile, '-O', level||2 );
            if (options.arg) arg = args.concat(options.arg);
            break;

        default:
            // Invoke the callback with a fail message
            done(new Error('Unable to determine file format'), null);
            return;
    }

    var originalSize = fs.statSync(inputFile).size;

    execFile(binPath, args, function(err, stdout, stderr) {

        if (verbose) {
            stdout && console.log(stdout);
            stderr && console.log(stderr);
        }

        options.stdout = stdout;
        options.stderr = stderr;

        if(!err){
            options.saved = originalSize - fs.statSync(outputFile).size;
        }

        done(err, options);
    });

};

// Task.JS API
exports.run = function (options, done) {

    var dest = options.dest;
    var file = exports.file;

    exports.async.forEach(exports.files, function(inputFile, cb){
        var outputFile = dest;
        // change to file copy to file
        if(file.isFile(inputFile) && file.isDirname(dest)){
            var filename = path.basename(inputFile);
            outputFile = path.join(dest, filename);
        }
        options.inputFile = inputFile;
        options.outputFile = outputFile;
        optimage(options, cb);

    }, done);
};