A Guide to Web Image Compression Software: ImageVice
Software type: GIF optimiser
ImageVice (odd spelling!) is a very clever and unconventional program to reduce the size of GIF and PNG files. (It also reduces BMP and PICT files or any other lossless file format, but that's not of immediate Web relevance.)
It does not so much modify the palette directly, as modify the image structure, to take advantage of the way files such as GIFs compress images. You can then use conventional GIF palette reducers to compress the file further.
GIFs use LZW compression, which looks at files in horizontal strips. The longer the continuous sequence of one color, the more it can be compressed. That's why quite large images with continuous single color backgrounds can be quite small files. Files with frequent changes in colour or intensity don't compress very well. That's why photographs don't compress efficiently as GIFs in most cases (aside from the colour depth problem).
ImageVice assists the GIF by creating strips of single colour in the image to take advantage of the LZW compression algorithm's strength.
The program is a filter plugin for Photoshop or other graphics editors that can use Photoshop plugins. It's activated from the "filters" menu.
When the first demo version came out late last year, it would only operate on a few images supplied with it. You couldn't try it out on your own images. That's why I didn't get around to reviewing it, as the supplied images were a bit odd and might well have been selected because they made it look good. I'm pleased to say the new version (1.1) will let you operate on any image, though with registration reminder screens. After 30 days or 100 images, it will also introduce a delay in its operation. Otherwise, it will let you use it as much as you like.
The program is quite complex to operate - it has five sliders that set particular elements - black level and white level cutoffs and ratios and a smoothing level. To be honest I've not yet fully mastered their subtleties, I've only gone as far as convincing myself it really does work. If you overdo the compression, your image may show horizontal smeared stripes. However, there is a guide to operating the program on Boxtop's web site. I'd suggest you read it or print it before playing with ImageVice.
After running ImageVice, you can then subject the image to further processing by a conventional GIF palette reducer, be it Boxtop's PhotoGIF or any other you like. (If you want to use Photoshop itself to save the modified image as a GIF, see the special "post production" instructions on the Boxtop site.)
The interface is clean and simple, and intuitive once you know what all the sliders do. It displays the "after" image on screen with the original in the background (in Photoshop or whatever). My only gripe is that the "after" image is small and there's no magnify control, so it can be quite hard to see what effects you've created with the controls. Boxtop know about this (see the readme file) but as the process is computationally intense, there are practical limits to what can be done (unless you have something like G3 266 or a Pentium 333).
The download file is moderate in size (736K for Windows) and installs quickly, though you need to tell it to select your Photoshop (or other image editor) plugins directory, as it does not default to this.
Conclusion: a unique and effective tool that's well worth looking at and learning to operate.
Links to information about web graphics compression, palettes and related matters of interest.
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