png-stream

A streaming PNG encoder and decoder for Node and the browser. Supports animated PNGs and normal still PNGs.

Installation

npm png-stream

For the browser, you can build using Browserify.

Decoding

This example uses the concat-frames module to collect the output of the PNG decoder into an array of frame objects.

var PNGDecoder = require('png-stream/decoder');
var concat = require('concat-frames');

// decode a PNG file to RGB pixels
fs.createReadStream('in.png')
  .pipe(new PNGDecoder)
  .pipe(concat(function(frames) {
    // frames is an array of frame objects
    // each one has a `pixels` property containing
    // the raw RGB pixel data for that frame, as
    // well as the width, height, etc.
  }));

Encoding

You can encode a PNG by writing or piping pixel data to a PNGEncoder stream. The PNG encoder supports writing data in the RGB, RGBA, grayscale (gray), and grayscale + alpha (gray) color spaces. You can also write data in the indexed color space by first quantizing it using the neuquant module.

var PNGEncoder = require('png-stream/encoder');
var neuquant = require('neuquant');

// convert a JPEG to a PNG
fs.createReadStream('in.jpg')
  .pipe(new JPEGDecoder)
  .pipe(new PNGEncoder)
  .pipe(fs.createWriteStream('out.png'));
  
// write indexed data
fs.createReadStream('in.jpg')
  .pipe(new JPEGDecoder)
  .pipe(new neuquant.Stream)
  .pipe(new PNGEncoder)
  .pipe(fs.createWriteStream('indexed.png'));

License

MIT