png-coder

About

This repo was forked from pngjs. png-coder adds support for encoding and decoding 16bit images along with 8bit images. Its a simple PNG encoder/decoder for Node.js with no native dependencies.

Installation

$ npm install png-coder

Example: 8bit images

var fs = require('fs'),
    PNG = require('png-coder').PNG;
 
// for 8-bit
fs.createReadStream('in.png')
    .pipe(new PNG({
        filterType: 4
    }))
    .on('parsed', function() {
 
        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'));
    });

Example: 16bit images

var fs = require('fs'),
    PNG = require('png-coder').PNG;
 
fs.createReadStream('in.png')
    .pipe(new PNG({
        filterType: -1
    }))
    .on('parsed', function() {
 
        for (var y = 0; y < this.height; y++) {
            for (var x = 0; x < this.width; x++) {
                var idx = (this.width * y + x) << (2 + this.depthInBytes - 1);
 
                // invert color
                this.data.writeUInt16BE(65535 - this.data.readUInt16BE(idx), idx);
                this.data.writeUInt16BE(65535 - this.data.readUInt16BE(idx+2), idx+2);
                this.data.writeUInt16BE(65535 - this.data.readUInt16BE(idx+4), idx+4);
 
                // and reduce opacity
                this.data.writeUInt16BE(this.data.readUInt16BE(idx+6) >> 1, idx+6);
            }
        }
 
        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). Interlaced mode is not supported.

Supported ancillary chunks

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

Class: PNG

PNG is readable and writable Stream.

Options

• width - use this with height if you want to create png from scratch
• height - as above
• depth - use this to specify 8 or 16 for a 8/16 bit image respectively.
• 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
• depth image depth - 8/16 bits
• 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) { }

png.parse(data, [callback])

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.

png.pack()

Starts converting data to PNG file Stream.

Returns this for method chaining.

png.bitblt(dst, sx, sy, w, h, dx, dy)

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.

Property: width

Width of image in pixels

Property: height

Height of image in pixels

Property: data

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

Property: gamma

Gamma of image (0 if not specified)

License

(The MIT License)

Copyright (c) 2015 Sisil Mehta

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.