Reading a PNG image in Node.js

Question

Is there an easy way in Node.js to read a PNG file and get the pixels of the image? Something like node-image, but the other way :)

I went through the libraries listed a

Answer 1

This one does both PNG decoding and encoding without native dependancies:

pngjs - PNG encoder/decoder for Node.js with no native dependencies.

An example for inverting the colors of a PNG:

var fs = require('fs'),
PNG = require('pngjs').PNG;

fs.createReadStream('in.png')
  .pipe(new PNG())
  .on('parsed', function() {

    for (var y = 0; y < this.height; y++) {
        for (var x = 0; x < this.width; x++) {
            var idx = (this.width * y + x) << 2;

            // invert color
            this.data[idx] = 255 - this.data[idx];
            this.data[idx+1] = 255 - this.data[idx+1];
            this.data[idx+2] = 255 - this.data[idx+2];

            // and reduce opacity
            this.data[idx+3] = this.data[idx+3] >> 1;
        }
    }

    this.pack().pipe(fs.createWriteStream('out.png'));
});