jpegtransmith

[jpegtran][jpegtran] engine for [spritesmith][spritesmith]. It uses jpegtran and [gm][gm] for lossless crop'n'drop, which allows it to
improve the quality on the edges in each image of the sprite.

[jpegtran]: http://jpegclub.org/jpegtran/
[gm]: http://aheckmann.github.io/gm/
[spritesmith]: https://github.com/Ensighten/spritesmith

Getting Started

Install the module with: npm install jpegtransmith

``js
var
spritesmith = require('spritesmith'), // or if using grunt-spritesmith: require('grunt-spritesmith/node_modules/spritesmith/src/smith.js')
jpegtransmith = require('jpegtransmith');

spritesmith.addEngine('jpegtransmith', jpegtransmith);

spritesmith({src: sprites, engine: 'jpegtransmith'}, function handleResult (err, result) {
result.image; // Binary string representation of image
result.coordinates; // Object mapping filename to {x, y, width, height} of image
result.properties; // Object with metadata about spritesheet {width, height}, see Requirements for possible disparities
});
`

NOTE: This module is slow, mainly because of jpegtran usage. If you have any suggestion in how to improve speed, open an issue.

Requirements

jpegtransmith depends on:
* [jpegtran][jpegtran], the download link is at the bottom in section 3, the binary must be globally accessible
* gm which depends on Graphics Magick.

For this to work, we use a virtual grid of 8x8 blocks. It requires your images dimensions to be multiple of 8, for the
jpegtran -drop command to work correctly. If you specify a padding in spritesmith, it must also be a multiple of 8.
If your images don't fit this description they will be used as-is but the individual images may be cropped and their generated dimensions
will be off by a few pixels (since they will be readjusted to align to 8x8), to correct the second problem you can use this (on grunt-spritesmith):

`js
var imdDataCache = {};

// Save the real img data for later use
jpegtransmith.imageDataMutator = function(imgData){
imgDataCache[imgData.file] = imgData;
}

// grunt config
// Restore the original width and height
sprite: {
my_sprite: {
// ...
cssVarMap: function(sprite){
var imgData = imgDataCache[sprite.source_image];
if(imgData){
sprite.width = imgData.realWidth;
sprite.height = imgData.realHeight;
}
}
}
}
`

> Alternatively, you can use ImageMagick which is implicitly discovered if gm is not installed.
> http://www.imagemagick.org/script/index.php

Documentation

This module was built to the specification for all spritesmith modules.

NOTE: This module fails most of the test in spritesmith-engine-test because it only works for JPEG images and it modifies the final size of the
sprite by adjusting each image to a 8x8 grid.

https://github.com/twolfson/spritesmith-engine-test

$3

These are options specific jpegtranmsith

- options Object
- quality Number: 92 - Quality of each image on a scale from 0 to 100 (All image edges will be in original quality)
- improvedEdgeSize Number: 8 - The number of pixels from the edge inwards to keep intact for the individual images in the final sprite
- bg String: black - The background color used on the sprite
- samplingFactor String`: 1x1,1x1,1x1

Contributing

Take care to maintain the existing coding style. Add unit tests for any new or changed functionality.

License

MIT
Copyright (c) 2014 Luis Hernandez