About
========
Simple PNG encoder/decoder for Node.js with no dependencies.

Based on [pngjs](https://github.com/niegowski/node-pngjs) with the follow enhancements.

  * Support for reading 1,2,4 & 16 bit files
  * Support for reading interlace files
  * Support for reading transparent colours
  * Sync interface as well as async
  * API compatible with pngjs and node-pngjs

Known lack of support for:

  * Animation
  * Gamma correction in 16 bit files

Tests
=====

 Tested using [PNG Suite](http://www.schaik.com/pngsuite/). To see tests, run `node test/test` and `view test/list.html`.

Installation
===============
```
$ npm install pngjs2  --save
```

Example
==========
```js
var fs = require('fs'),
    PNG = require('node-png').PNG;

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'));
    });
```
For more examples see `examples` folder.

API
================

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: PNG
`PNG` 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
- `interlace` image is interlaced


### 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. Can be `String` or `Buffer`. 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.

+#### Example
```js
new PNG({ filterType:4 }).parse( imageData, function(error, data)
{
	console.log(error, data)
});
```

### 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 a rectangle of pixels from current (i.e. the source) image (`sx`, `sy`, `w`, `h`) to `dst` image (at `dx`, `dy`).

Returns `this` for method chaining.

For example, the following code copies the top-left 100x50 px of `in.png` into dst and writes it to `out.png`:
```js
var dst = new PNG({filterType: -1, width: 100, height: 50});
fs.createReadStream('in.png')
    .pipe(new PNG({
        filterType: -1
    }))
    .on('parsed', function() {
        this.bitblt(dst, 0, 0, 100, 50, 0, 0);
        dst.pack().pipe(fs.createWriteStream('out.png'));
    });
```


### 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)

Changelog
============

### 0.0.2 - 02/08/2015
  - Bugfixes to interlacing, support for transparent colours

### 0.0.1 - 02/08/2015
  - Initial release, see pngjs for older changelog.

License
=========

(The MIT License)

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.
