png-chunk-stream

Windows	Mac/Linux

A small simple helper for working with PNG files, inspired by chunky-stream. It is supposed to be lightweight and usable with browserify. There is another more complete module called streampng.

npm install png-chunk-stream

Decode and Encode PNGs into objects of chunks like this:

{ length: 13,
  type: 'IHDR',
  data: <Buffer 00 00 02 01 00 00 01 68 08 06 00 00 00>,
  crc: <Buffer ce f5 28 6e> }

For the encode function the crc and length attributes can be omitted and will be calculated from the data attribute.

Example

Create some funky glitch art like this:

var fs = require('fs')
var decoder = require('./').decode()
var encoder = require('./').encode()
var through = require('through2')
 
fs.createReadStream('test.png')
  .pipe(decoder)
  .pipe(through.obj(function (chunk, enc, cb) {
    if(chunk.type === 'IHDR') {
      console.log('height', chunk.data.readUInt32BE(0))
      chunk.data.writeUInt32BE(512, 0)
      chunk.crc = null // recalculate
    }
    this.push(chunk)
    cb()
  }))
  .pipe(encoder)
  .pipe(fs.createWriteStream('out.png'))

CLI

You can also install the module globally with the -g flag. This will add a png-chunk script with the commands encode and decode. The buffers will be encoded as base64.

$ png-chunk decode < test.png | head -2
{"length":13,"type":"IHDR","data":"AAACAQAAAWgIBgAAAA==","crc":"zvUobg=="}
{"length":25,"type":"tEXt","data":"U29mdHdhcmUAQWRvYmUgSW1hZ2VSZWFkeQ==","crc":"ccllPA=="}
$ png-chunk decode < test.png | png-chunk encode > out.png
(this basically copes test.png to out.png)