png.js

PNG.js
======

PNG.js is a PNG decoder fully written in JavaScript. It works in Node.js as
well as in (modern) browsers.

Usage
-----

`` js
var PNGReader = require('png.js');

var reader = new PNGReader(bytes);
reader.parse(function(err, png){
if (err) throw err;
console.log(png);
});

`

Or with options:

` js
reader.parse({
data: false
}, function(err, png){
if (err) throw err;
console.log(png);
});

`

Currently the only option is:

- data (boolean) - should it read the pixel data, or only the image information.

$3

The PNG object is passed in the callback. It contains all the data extracted
from the image.

` js
// most importantly
png.getWidth();
png.getHeight();
png.getPixel(x, y); // [red, blue, green, alpha]
// but also
png.getBitDepth();
png.getColorType();
png.getCompressionMethod();
png.getFilterMethod();
png.getInterlaceMethod();
png.getPalette();
`

Using PNGReader in Node.js
--------------------------

PNGReader accepts an Buffer object, returned by fs.readFile, for example:

` js
fs.readFile('test.png', function(err, buffer){

var reader = new PNGReader(buffer);
reader.parse(function(err, png){
if (err) throw err;
console.log(png);
});

});
`

Using PNGReader in the Browser
------------------------------

PNGReader accepts a byte string, array of bytes or an ArrayBuffer.

For example using FileReader with file input fields:

`js
var reader = new FileReader();

reader.onload = function(event){
var reader = new PNGReader(event.target.result);
reader.parse(function(err, png){
if (err) throw err;
console.log(png);
});
};

fileInputElement.onchange = function(){
reader.readAsArrayBuffer(fileInputElement.files[0]);
// or, but less optimal
reader.readAsBinaryString(fileInputElement.files[0]);
};
`

Or instead of using input elements, XHR can also be used:

`js
var xhr = new XMLHttpRequest();
xhr.open('GET', 'image.png', true);
xhr.responseType = 'arraybuffer';

xhr.onload = function(e){
if (this.status == 200){
var reader = new PNGReader(this.response);
reader.parse(function(err, png){
if (err) throw err;
console.log(png);
});
}
};

xhr.send();
``

Building Browser Version
------------------------

PNG.js uses CommonJS modules which can be used in browsers after building it
with browserify:

browserify ./PNGReader.js -s PNGReader