png-async

A simple and non-blocking PNG encoder / decoder.

Usage no npm install needed!

<script type="module">
  import pngAsync from 'https://cdn.skypack.dev/png-async';
</script>

README

png-async

A simple and non-blocking PNG encoder / decoder for Node.

npm version Linux Build Windows Build devDependency Status

forked from node-png.

Install

$ npm install png-async --save

Build (for Developers)

$ git clone https://github.com/kanreisa/node-png-async.git
$ cd node-png-async
$ npm install
$ npm run build
$ npm run test

Example

var fs = require('fs');
var png = require('png-async');

fs.createReadStream('in.png')
    .pipe(png.createImage({
        filterType: 4
    }))
    .on('parsed', function () {

        // Note: this is blocking. be careful.
        for (var y = 0; y < this.height; y++) {
            for (var x = 0; x < this.width; x++) {
                var idx = (this.width * y + x) << 2;

                // invert color
                this.data[idx] = 255 - this.data[idx];
                this.data[idx+1] = 255 - this.data[idx+1];
                this.data[idx+2] = 255 - this.data[idx+2];

                // and reduce opacity
                this.data[idx+3] = this.data[idx+3] >> 1;
            }
        }

        this.pack().pipe(fs.createWriteStream('out.png'));
    });

For more examples see examples folder.

Documentation

As input any color type is accepted (grayscale, rgb, palette, grayscale with alpha, rgb with alpha) but 8 bit per sample (channel) is the only supported bit depth. Interlaced mode is not supported.

Supported ancillary chunks

  • gAMA - gamma,
  • tRNS - transparency (but only for paletted image)

Class: Image

Image is readable and writable Stream.

Options

  • width - use this with height if you want to create png from scratch
  • height - as above
  • checkCRC - whether parser should be strict about checksums in source stream (default: true)
  • deflateChunkSize - chunk size used for deflating data chunks, this should be power of 2 and must not be less than 256 and more than 32*1024 (default: 32 kB)
  • deflateLevel - compression level for delate (default: 9)
  • deflateStrategy - compression strategy for delate (default: 3)
  • filterType - png filtering method for scanlines (default: -1 => auto, accepts array of numbers 0-4)

Event "metadata"

function(metadata) { } Image's header has been parsed, metadata contains this information:

  • width image size in pixels
  • height image size in pixels
  • palette image is paletted
  • color image is not grayscale
  • alpha image contains alpha channel

Event: "parsed"

function(data) { } Input image has been completly parsed, data is complete and ready for modification.

Event: "error"

function(error) { }

Image#parse(data: Buffer, callback?: (err: Error, image: Image) => void): Image

Parses PNG file data. Alternatively you can stream data to instance of PNG.

Optional callback is once called on error or parsed. The callback gets two arguments (err, data).

Returns this for method chaining.

Image#pack(): Image

Starts converting data to PNG file Stream.

Returns this for method chaining.

Image#bitblt(dst: Image, sx: number, sy: number, w: number, h: number, dx: number, dy: number): Image

Helper for image manipulation, copies rectangle of pixels from current image (sx, sy, w, h) to dst image (at dx, dy).

Returns this for method chaining.

Image#width: number

Width of image in pixels

Image#height: number

Height of image in pixels

Image#data: Buffer

Buffer of image pixel data. Every pixel consists 4 bytes: R, G, B, A (opacity).

Image#gamma: number

Gamma of image (0 if not specified)

License

MIT