jpeg-js

A pure javascript JPEG encoder and decoder for node.js

NOTE: this is a _synchronous_ (i.e. CPU-blocking) library that is much slower than native alternatives. If you don't need a _pure javascript_ implementation, consider using async alternatives like sharp in node or the Canvas API in the browser.


Installation

This module is installed via npm:

``bash
$ npm install jpeg-js
`

Example Usage

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Will decode a buffer or typed array into a Buffer;

`js
var jpeg = require('jpeg-js');
var jpegData = fs.readFileSync('grumpycat.jpg');
var rawImageData = jpeg.decode(jpegData);
console.log(rawImageData);
/*
{ width: 320,
height: 180,
data: }
*/
`

To decode directly into a Uint8Array, pass useTArray: true in options
decode:

`js
var jpeg = require('jpeg-js');
var jpegData = fs.readFileSync('grumpycat.jpg');
var rawImageData = jpeg.decode(jpegData, {useTArray: true}); // return as Uint8Array
console.log(rawImageData);
/*
{ width: 320,
height: 180,
data: { '0': 91, '1': 64, ... } } // typed array
*/
`

#### Decode Options

| Option | Description | Default |
| -------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------- |
| colorTransform | Transform alternate colorspaces like YCbCr. undefined means respect the default behavior encoded in metadata. | undefined |
| useTArray | Decode pixels into a typed Uint8Array instead of a Buffer. | false |
| formatAsRGBA | Decode pixels into RGBA vs. RGB. | true |
| tolerantDecoding | Be more tolerant when encountering technically invalid JPEGs. | true |
| maxResolutionInMP | The maximum resolution image that jpeg-js should attempt to decode in megapixels. Images larger than this resolution will throw an error instead of decoding. | 100 |
| maxMemoryUsageInMB | The (approximate) maximum memory that jpeg-js should allocate while attempting to decode the image in mebibyte. Images requiring more memory than this will throw an error instead of decoding. | 512 |

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`js
var jpeg = require('jpeg-js');
var width = 320,
height = 180;
var frameData = new Buffer(width height 4);
var i = 0;
while (i < frameData.length) {
frameData[i++] = 0xff; // red
frameData[i++] = 0x00; // green
frameData[i++] = 0x00; // blue
frameData[i++] = 0xff; // alpha - ignored in JPEGs
}
var rawImageData = {
data: frameData,
width: width,
height: height,
};
var jpegImageData = jpeg.encode(rawImageData, 50);
console.log(jpegImageData);
/*
{ width: 320,
height: 180,
data: }
*/
// write to file
fs.writeFileSync('image.jpg', jpegImageData.data);
``

License

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This library builds on the work of two other JPEG javascript libraries,
namely jpgjs for the decoding
which is licensed under the Apache 2.0 License below:

Copyright 2011 notmasteryet

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

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The encoding is based off a port of the JPEG encoder in as3corelib.

The port to Javascript was done by by Andreas Ritter, www.bytestrom.eu, 11/2009.

The Adobe License for the encoder is:

Adobe

Copyright (c) 2008, Adobe Systems Incorporated
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

- Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.

- Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

- Neither the name of Adobe Systems Incorporated nor the names of its
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Contributing

jpeg-js is an OPEN Open Source Project. This means that:

> Individuals making significant and valuable contributions are given commit-access to the project to contribute as they see fit. This project is more like an open wiki than a standard guarded open source project.

See the CONTRIBUTING.md file for more details.

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jpeg-js is only possible due to the excellent work of the following contributors: