PNG.js
PNG.js is a PNG decoder fully written in JavaScript. It works in Node.js as well as in (modern) browsers.
Usage
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:
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.
PNG object
The PNG object is passed in the callback. It contains all the data extracted from the image.
// most importantly
png.getWidth();
png.getHeight();
png.getPixel(x, y); // [red, blue, green, alpha]
png.getRGBA8Array(); // [r1, g1, b1, a1, r2, b2, g2, a2, ... ] - Same as canvas.getImageData
// 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:
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:
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:
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