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Alpha JPEG - Images with transparency using JPEG compression.

Create your own Alpha JPEGs here: https://craigthings.github.io/alpha-jpeg/

Alpha JPEGs contain both the visible pixels and transparent pixels. Alpha JPEGs, when loaded using the Alpha JPEG loader, appear like PNGs but take advantage of JPEG compression.

Alpha JPEG is made up of 3 parts.

  1. The Alpha JPEG Generator. Use it to create Alpha JPEGs. Drop a PNG, adjust the quality and download your Alpha JPEG.
  2. A JavaScript library for loading the Alpha JPEG image. The javascript contains a loader that loads the Alpha JPEG and converts it into a transparent image in the DOM.
  3. A Photoshop Action that converts a PNG into an "Alpha JPEG" in Adobe Photoshop. This is useful for making mangual adjustments.

Setup

There are 3 ways to use Alpha JPEG:

NPM

npm install alpha-jpeg

And just require it:

var AlphaJPEG = require('alpha-jpeg');

Script Tag

Load it directly with a script tag. Download the compiled and minified library from:

/build/alpha-jpeg.min.js

Upload it anywhere you like and include it with a script tag:

<script src="alpha-jpeg.min.js"></script>

Common JS Module

Download the commonjs module located from:

/src/utils/AlphaJPEG.js

Save it anywhere you like in your development environment, and include it like normal:

var AlphaJPEG = require('./utils/AlphaJPEG');

Usage

The Alpha JPEG loader requires JPEGs that are exported using the Alpha JPEG Photoshop Action. Read the Creating Alpha JPEGs section for instructions.

Once you've got an image exported, load it like this:

AlphaJPEG.load('#birdContainer', 'images/bird.alpha.jpg');

If you preffer to load the javascript libraries directly using script tags or other methods, you can use this stand-alone version of the library:

/build/alpha-jpeg.min.js

This repository also includes a commonjs module version of the code located here:

/src/utils/AlphaJPEG.js

Methods

AlphaJPEG.load ( target, imageURL, [options] )

Loads the given JPEG into the target. When the animation is completely loaded, the callback is called passing a reference to the Alpha JPEG DOM element.

Options

Alpha JPEG methods accept an optional options object. The options are:

pixelRatio (default: 1) Number

This option increases the pixel density of the image. If your asset is, for example, targeting an iPhone 5 and your Alpha JPEG is exported at retina resolution, you'll probably want to set this to "2".

onComplete Function

Sets a callback function for when the image is fully loaded and rendered. This passes a reference to the Alpha JPEG DOM element as an argument.

Creating Alpha JPEGs

Alpha JPEG Generator

  1. Head to https://craigthings.github.io/alpha-jpeg/

  2. Find a PNG on your computer, drag and drop it in the dashed "Source" box.

  3. Choose a quality setting and hit "Generate". A preview of the compressed Alpha JPEG will appear below in the "Result" box. Feel free to adjust the quality setting and hit "Generate" until you like the results.

  4. Click "Download" below the "Result" image to download the Alpha JPEG.

Photoshop Action

  1. Install the Alpha JPEG Photoshop Actions by double-clicking on the photoshop action located here:

    /actions/Alpha JPEG.atn

  2. Open the PNG (not PSD) you'd like to convert to an Alpha JPEG.

  3. Open the Actions panel (Alt+F9 / Option+F9).

  4. Click the arrow next to "Alpha JPEG".

  5. Click on "Make Alpha JPEG".

  6. Click the "play" button at the bottom of the Actions panel.

  7. You'll see the visible pixels on the top, and the alpha channel pixels on the bottom. Make any adjustments you need and save your asset out as a JPEG.

How to develop and build

npm run build:prod    # Build library for portable use.
npm run dev    # Run the demo as a live dev server.

Examples

JavaScript library (must be run on an HTTP server)

This example uses the compiled JavaScript library version of Alpha JPEG. You can find it here:

/demo/demo.js