jspng

Generate unoptimized PNG images from raw pixel data.

Install

$ npm install jspng

Example

var fs    = require('fs');
var jspng = require('jspng');

var pixels = jspng.Buffer(128 * 128 * 4).fill(new Buffer([ 0x00, 0x00, 0xff, 0x88 ]));

var png = new jspng(pixels, { width: 128, height: 128, inputmode: 'rgba', meta: { 'Software': jspng.VERSION }});

fs.writeFileSync('jspng.png', png.toBuffer());

For more examples see examples folder.

Documentation

The jspng package was created to run in both server-side application using NodeJS 0.12 as well as in most - if not all - modern Browsers but specifically Mozilla Firefox 56+ and Chromium 61+.

Its initial use case was the creation of dynamically generated PNG textures for X3D models, which were at first generated and previewed in a clientside Browser application using X3DOM and then stored by a server process which regenerated the textures based on parameters provided by the client, rather than being send the whole client-generated binary PNG file.

While originally being developed for NodeJS, Browser support was added by implementing a shim stub of NodeJS's Buffer class in ECMAScript (being the basis for all modern Browser's Javascript implemenation) using TypedArray classes and subclasses.

Furthermore the implementation had to remain dependence-free due to the very different APIs for handling binary data present in the server and client environment, which results in jspng not implementing any kind of compression of the image data in PNG. While this creates unusually big PNG files, the data is quickly decoded when needed; a plus in our X3DOM and any similar use case.

Features

Beside the support for truecolor and greyscale PNG images with and without alpha, adding meta data is supported. See the example above.

Input modes

The raw pixel data supplied to create the image is somewhat freely configurable, as long as color and alpha data is provided as 8 bits per channel. The default format is 'rgba', a basic 32bit-per-pixel format expecting the red, green and blue color data first, followed by an 8-bit alpha channel.

Color and alpha channels can furthermore be freely arranged or even dropped using the inputmode option. 'argb' would interpret the pixel data as starting with the alpha channel, followed by red, green and blue channel. Each pixel would still be 32-bit in size in this example.

A set of-8 bit data points can be visualized in a black-to-red PNG imagemap by using 'r', meaning that each pixel only 8-bits in size.

Using '...b' on pixel data that is actually encoded in RGBA-format would ignore the first 24 bits of each pixel and visualize the alpha channel as blue in the resulting PNG.

Image dimension prediction

While you are strongly encouraged to provide the width and height of the image described by your pixel data, jspng will try to estimate the image dimenstions should you choose not to. Should one or both dimensions not be specified, jspng will use the size of the provided pixel data buffer to fit all pixels into the image.

Providing neither width nor height, jspng will assume the image data should be arranged as a square.

Limitations

• As mentioned there is no compression of image data of any kind, should small image size be desired.
• Indexed/paletted images are not supported.
• 16-bit color and alpha channel depth is not supported.