pngjs3

Simple PNG encoder/decoder for Node.js and browsers with no dependencies.

A fork from pngjs. The package is prepared for the browser and there are some changes in the exports. The pngjs has been extended with the following enhancements:

skipRescale that allows retrieval of 16-bit data if input was 16-bit
grayscaleData for retrieving the grayscale bitmap (note ignores alpha channel and caches the grayscale conversion†)
propData for retrieving the proportional values (note ignores alpha channel and caches the proportional conversion†)

† If you manipulate the data property of the object directly the conversions will not be recalculated due to the cache.

The pngjs had the follow enhancements compared to the original:

Support for reading 1, 2, 4 & 16 bit files
Support for reading interlace files
Support for reading tTRNS transparent colours
Support for writing colortype 0 (grayscale), colortype 2 (RGB), colortype 4 (grayscale alpha) and colortype 6 (RGBA)
Sync interface as well as async
API compatible with pngjs and node-pngjs

Known lack of support for:

Extended PNG e.g. Animation
Writing in colortype 3 (indexed color)

Requirements
Comparison Table
Tests
Installation
Browser
Example
Async API
Sync API
Changelog

Requirements

Node.js v10 or later

Comparison Table

Name	Forked From	Sync	Async	16 Bit	1/2/4 Bit	Interlace	Gamma	Encodes	Tested
pngjs3	pngjs	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
pngjs		Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
node-png	pngjs	No	Yes	No	No	No	Hidden	Yes	Manual
png-coder	pngjs	No	Yes	Yes	No	No	Hidden	Yes	Manual
pngparse		No	Yes	No	Yes	No	No	No	Yes
pngparse-sync	pngparse	Yes	No	No	Yes	No	No	No	Yes
png-async		No	Yes	No	No	No	No	Yes	Yes
png-js		No	Yes	No	No	No	No	No	No

Native C++ node decoders:

png
png-sync (sync version of above)
pixel-png
png-img

Tests

Tested using PNG Suite. We read every file into pngjs, output it in standard 8bit colour, synchronously and asynchronously, then compare the original with the newly saved images.

To run the tests, fetch the repo (tests are not distributed via npm) and install with npm i, run npm test.

The only thing not converted is gamma correction - this is because multiple vendors will do gamma correction differently, so the tests will have different results on different browsers.

Installation

$ npm install pngjs3  --save

or with yarn

$ yarn add pngjs3

Browser

The package has been build with browser support using browserify-zlib instead of NodeJS' zlib.

Example

import fs from 'fs';
import PNG from 'pngjs3';

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.

Async API

As input any color type is accepted (grayscale, rgb, palette, grayscale with alpha, rgb with alpha) with 8 & 16 bit per sample (channel) are the supported bit depths. Interlaced mode is not supported.

Class: PNG

PNG is a readable and writable Stream.

Options

id - An optional identifier can be provided if you want to be able to track this object in memory.
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 deflate (default: 9).
deflateStrategy - compression strategy for deflate (default: 3).
deflateFactory - deflate stream factory (default: zlib.createDeflate).
filterType - png filtering method for scanlines (default: -1 => auto, accepts array of numbers 0-4).
colorType - the output colorType - see constants. 0 = grayscale, no alpha, 2 = color, no alpha, 4 = grayscale & alpha, 6 = color & alpha. Default currently 6, but in the future may calculate best mode.
inputColorType - the input colorType - see constants. Default is 6 (RGBA).
bitDepth - the bitDepth of the output, 8 or 16 bits. Input data is expected to have this bit depth. 16 bit data is expected in the system endianness (Default: 8).
inputHasAlpha - whether the input bitmap has 4 bytes per pixel (rgb and alpha) or 3 (rgb - no alpha).
bgColor - an object containing red, green, and blue values between 0 and 255. that is used when packing a PNG if alpha is not to be included (default: 255,255,255).
skipRescale - set to true if you want to skip the rescaling to 8-bit bitmap. This is good if you wish to retain a 16-bit bitmap datastructure.
initGrayscaleData - if you want to initialize the grayscale conversion of the RGBA data for the grayscaleData call †.
initPropData - boolean or an object with the arguments to initPropData for initializing the propData †.

† These functions are useful if you wish to do repeated manipulations to the image and as image manipulation is time consuming it is beneficial to initiate the data from start.

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 completely 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

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.destroy()

Calling destroy() is entirely optional but browser memory management is both tricky and important, this is especially important here as images are take up a lot of space. The problem is also due to that the async procedures associated with the class can cause unwanted side-effects such memory leaks as we expect the object to have been deleted together with a DOM-node. The call tries to clear all the ArrayBuffers both own buffers and other sub-buffers that can be problematic.

bitblt({ dst, srcX, srcY, width, height, deltaX, deltaY })

Helper for image manipulation, copies a rectangle of pixels from current (i.e. the source) image (srcX, srcY, width, height) to dst image (at deltaX, deltaY).

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:

const dst = new PNG({ width: 100, height: 50 });
fs.createReadStream('in.png')
  .pipe(new PNG())
  .on('parsed', function () {
    this.bitblt({
      dst,
      srcX: 0,
      srcY: 0,
      width: 100,
      height: 150,
      deltaX: 0,
      deltaY: 0,
    });
    dst.pack().pipe(fs.createWriteStream('out.png'));
  });

Not that the package exports bitblt that takes the additionalargument src;

Property: adjustGamma()

Helper that takes data and adjusts it to be gamma corrected. Note that it is not 100% reliable with transparent colours because that requires knowing the background colour the bitmap is rendered on to.

In tests against PNG suite it compared 100% with chrome on all 8 bit and below images. On IE there were some differences.

The following example reads a file, adjusts the gamma (which sets the gamma to 0) and writes it out again, effectively removing any gamma correction from the image.

fs.createReadStream('in.png')
  .pipe(new PNG())
  .on('parsed', function () {
    this.adjustGamma();
    this.pack().pipe(fs.createWriteStream('out.png'));
  });

Property: width

Width of image in pixels

Property: height

Height of image in pixels

Property: shape

Object with height and width

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)

Serializing and deserializing

When using libraries suchs as Redux it is "highly recommended that you only put plain serializable objects, arrays, and primitives into your store". For this purpose PNGJS has implemented the serialize() and static deserialize() methods.

import PNG from 'pngjs3';

myPNG = new PNG();
...

const data2store = myPNG.serialize();
...

const myRecreatedObject = PNG.deserialize(data2store);

// Note that:
console.log(myRecreatedObject !== myPNG, 'A new object has been created');
console.log(myRecreatedObject.storage === myPNG.storage, 'But the storage (i.e. data) is the same');

Immutability

The storage in the PNG-object is immutable through immer. This means that any changes to the storage will propagate from subitem to the top item. This allows for efficient comparison store === prevStore.

Packing a PNG and removing alpha (RGBA to RGB)

When removing the alpha channel from an image, there needs to be a background color to correctly convert each pixel's transparency to the appropriate RGB value. By default, pngjs will flatten the image against a white background. You can override this in the options:

import fs from 'fs';
import PNG from 'pngjs3';

fs.createReadStream('in.png')
  .pipe(
    new PNG({
      colorType: 2,
      bgColor: {
        red: 0,
        green: 255,
        blue: 0,
      },
    }),
  )
  .on('parsed', function () {
    this.pack().pipe(fs.createWriteStream('out.png'));
  });

Sync API

read(buffer)

Take a buffer and returns a PNG image. The properties on the image include the meta data and data as per the async API above.

import { sync as PNGSync } from 'pngjs3';

const data = fs.readFileSync('in.png');
const png = PNGSync.read(data);

write(png)

Take a PNG image and returns a buffer. The properties on the image include the meta data and data as per the async API above.

import { sync as PNGSync } from 'pngjs3';

const data = fs.readFileSync('in.png');
const png = PNGSync.read(data);
const options = { colorType: 6 };
const buffer = PNGSync.write(png, options);
fs.writeFileSync('out.png', buffer);

Adjust Gamma

Adjusts the gamma of a sync image. See the async adjustGamma.

import { adjustGamma } from 'pngjs3';

const data = fs.readFileSync('in.png');
const png = PNGSync.read(data);
adjustGamma(png);

Changelog

--> 6.1.1 - 19/06/2023

Update package dependencies
Fixed bad es6 reference
Node support updated to 18 (but no changes in code that should break older versions)

--> 6.1.0 - 30/10/2020

Added optional ID for easier tracking the object in memory
Added destroy() to PNG class. Browser memory management could potentially be problematic as the async procedures associated with the class can cause unwanted side-effects such memory leaks as we expect the object to have been deleted together with a DOM-node.

--> 6.0.0 - 28/10/2020

BREAKING - Sync version now throws if there is unexpected content at the end of the stream.
BREAKING - Drop support for node 10 (Though nothing incompatible in this release yet)

--> 5.1.10 - 21/07/2020

Update package dependencies
Fixed rollup issues
Removed circular dependency

--> 5.1.9 - 25/05/2020

Update package dependencies
Added changes implemented in original pngjs

--> 5.1.7 - 05/04/2020

Update package dependencies
Converted Buffer() to Buffer.from & Buffer.alloc
Drop support for Node v8

--> 5.1.5 - 25/08/2019

Update package dependencies

5.1.0 - 07/05/2019

Implemented immutable store (setters and getters should allow for the same functionality as before) - issue #49
There is a shape attribute with the width and the height
For storage you can now use serialize() and static deserialize()

5.0.4 - 04/05/2019

Added with commits from original fork (https://github.com/lukeapage/pngjs) implemented fixes and improvements should now match
Updated packages

5.0.3 - 23/04/2019

Homepage url + package updates

5.0.2 - 17/04/2019

Updated packages

5.0.1 - 02/12/2019

Updated packages

5.0.0 - 01/01/2019

BREAKING: The sync is exported as sync and no longer a static member of the PNG-class
Default export is now the PNG class
Separate export for adjustGamma, bitblt and sync
The bitblt now expects an object as argument due to too many arguments
Updated the README to match the new structure

4.0.0 - 03/08/2018

Change to browserify-zlib (causes one async test case to fail :-()

3.6.2 - 03/08/2018

Change to rollup - now includes es6 module, umd and cjs
Package updates
Fixes to buggy flow interface

3.5.0 - 17/01/2018

Added propData2ImageClamped for copying propData into Uint8ClampedArray

3.4.2 - 8/01/2018

Fixed bug in propData
Changed min/max value search to for loop with break

3.4.1 - 7/01/2018

Fixed bug in grayscaleData for rgb
Fixed Flow typings with all the sub-elements

3.4.0 - 22/12/2017

Fork to pngjs3
Added browserify for browser loading
Added propData and grayscaleData
Added Flow typings

3.3.1 - 15/11/2017

Bugfixes and removal of es6

3.3.1 - 15/11/2017

Bugfixes and removal of es6

3.3.0

Add writing 16 bit channels and support for grayscale input

3.2.0 - 30/04/2017

Support for encoding 8-bit grayscale images

3.1.0 - 30/04/2017

Support for pngs with zlib chunks that are malformed after valid data

3.0.1 - 16/02/2017

Fix single pixel pngs

3.0.0 - 03/08/2016

Drop support for node below v4 and iojs. Pin to 2.3.0 to use with old, unsupported or patched node versions.

2.3.0 - 22/04/2016

Support for sync in node 0.10

2.2.0 - 04/12/2015

Add sync write api
Fix newfile example
Correct comparison table

2.1.0 - 28/10/2015

rename package to pngjs
added 'bgColor' option

2.0.0 - 08/10/2015

fixes to readme
breaking change - bitblt on the png prototype now doesn't take a unused, unnecessary src first argument

1.2.0 - 13/09/2015

support passing colorType to write PNG's and writing bitmaps without alpha information

1.1.0 - 07/09/2015

support passing a deflate factory for controlled compression

1.0.2 - 22/08/2015

Expose all PNG creation info

1.0.1 - 21/08/2015

Fix non square interlaced files

1.0.0 - 08/08/2015

More tests
source linted
maintainability refactorings
async API - exceptions in reading now emit warnings
documentation improvement - sync api now documented, adjustGamma documented
breaking change - gamma chunk is now written. previously a read then write would destroy gamma information, now it is persisted.

0.0.3 - 03/08/2015

Error handling fixes
ignore files for smaller npm footprint

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.

hearhellacopters/pngjs3

pngjs3

Table of Contents

Requirements

Comparison Table

Tests

Installation

Browser

Example

Async API

Class: PNG

Options

Event "metadata"

Event: "parsed"

Event: "error"

png.parse(data, [callback])

Example

png.pack()

png.destroy()

bitblt({ dst, srcX, srcY, width, height, deltaX, deltaY })

Property: adjustGamma()

Property: width

Property: height

Property: shape

Property: data

Property: gamma

Serializing and deserializing

Immutability

Packing a PNG and removing alpha (RGBA to RGB)

Sync API

read(buffer)

write(png)

Adjust Gamma

Changelog

--> 6.1.1 - 19/06/2023

--> 6.1.0 - 30/10/2020

--> 6.0.0 - 28/10/2020

--> 5.1.10 - 21/07/2020

--> 5.1.9 - 25/05/2020

--> 5.1.7 - 05/04/2020

--> 5.1.5 - 25/08/2019

5.1.0 - 07/05/2019

5.0.4 - 04/05/2019

5.0.3 - 23/04/2019

5.0.2 - 17/04/2019

5.0.1 - 02/12/2019

5.0.0 - 01/01/2019

4.0.0 - 03/08/2018

3.6.2 - 03/08/2018

3.5.0 - 17/01/2018

3.4.2 - 8/01/2018

3.4.1 - 7/01/2018

3.4.0 - 22/12/2017

3.3.1 - 15/11/2017

3.3.1 - 15/11/2017

3.3.0

3.2.0 - 30/04/2017

3.1.0 - 30/04/2017

3.0.1 - 16/02/2017

3.0.0 - 03/08/2016

2.3.0 - 22/04/2016

2.2.0 - 04/12/2015

2.1.0 - 28/10/2015

2.0.0 - 08/10/2015

1.2.0 - 13/09/2015

1.1.0 - 07/09/2015

1.0.2 - 22/08/2015

1.0.1 - 21/08/2015

1.0.0 - 08/08/2015

0.0.3 - 03/08/2015

0.0.2 - 02/08/2015

0.0.1 - 02/08/2015

License