By Graham Northup — The Geek Squad

OK, everyone, can we stop assuming that JPEG is the absolute best file format around? I mean, sure, if you want digital compression, few things are better, but JPEG is lossy, which means every time you edit and save and edit and save an image to the JPEG file format, you’ll lose some data. Additionally, it destroys nice clean edges, makes weird artifacts in text that can make it look fuzzy, and turns solid colors into murky mixes of various shades.

But I know you like compression. After all my recently completed desktop background would be a 30 megabyte 24-bit RGB bitmap, which would make even “high-speed” connections around here choke for a few seconds. But it has a lot of solid color, and some color gradients in a few areas, with a not-too-complicated subject in the middle. Therein lies the problem–JPEG would destroy those clean gradients and white whites, turning it into a noisy mess of cyans, yellows, and magentas.

So what should one do, then? In 1987, CompuServe created the Graphics Interchange Format, GIF, as a way to replace their previous image format which used Run Length Encoding (RLE, a rather weak compression algorithm). The GIF format used a palette of 256 colors, and stored one 8-bit byte for every pixel. In addition, one value could be used as a transparency, thus allowing for masked images that could be placed above others with a clean border. But the format was limited, and slowly displays that could handle more than 256 colors were coming onto the market. Further, patents on the compression algorithm used (LZW) hindered the development of GIF-compatible software.

So, in 1995, a few motivated people on a usenet group created the Portable Network Graphics file format. In it, they used the zlib compression scheme (the same as used by .zip files), which was unencumbered by patents, and decided to release it as unpatented as well. One could still use a palette of 256 colors if they wanted to, but the extensible format also allowed for varying bit depths, including 16 bit “High Color”, 24 bit “True Color”, and, as good as it gets right now, 32-bit RGBA. Furthermore, that same desktop background becomes 265 kilobytes when compressed. That’s almost a 116:1 compression ratio! And did I mention that this image has that 8-bit alpha channel, too?

OK, OK, zlib doesn’t work for everything. It worked very well here because of all the solid colors and simple patterns (like gradients) present in a CG rendering. It really begins to fall apart when one takes photographs, where little variations in color don’t make much of a difference to the eye. This is where JPEG shines. But for everything else, INCLUDING image editing, use lossless formats. Because if you edit an image, and the person next to you edits it again, and you’re bothing using JPEG, you’ll be slowly degrading the quality with each edit. I’ve taken JPEGs, edited them, and saved them as PNGs; it’s not wrong to do so.  Furthermore, if you’re really into computer editing, you’ll probably find a whole bunch of other, more-or-less obscure formats like TARGA (which acts like BMP, PNG, and JPEG rolled into one), which is actually the format used by the textures of the objects in that rendered scene anyways. You’ll also find layered image formats, supported specifically by layered image editors, including GIMP and PhotoShop.

So, all in all, don’t use JPEG for image editing. Don’t use JPEG for simple colors, block diagrams, and text. And don’t just ask “oh, just put it in JPEG because that’s the only thing [INSERT PROGRAM NAME HERE] understands”, because in all likelihood, that’s probably not true. (At the very least, most programs will accept raw, uncompressed  bitmap images.)

Simple Images
Format	Image	400% Image (as PNG)	Filesize	Fullness
Bitmap			65,590 bytes	100%
Portable Network Graphics (PNG)			5,841 bytes	8.9%
Joint Photo Experts Group (JPEG), 85% Quality			1,982 bytes	3.0%
Joint Photo Experts Group (JPEG), 100% Quality			5,270 bytes	8.0%

Photos
Format	Image	400% Image (as PNG)	Filesize	Fullness
Bitmap			65,590 bytes	100%
Portable Network Graphics (PNG)			37,403 bytes	57.0%
Joint Photo Experts Group (JPEG), 85% Quality			5,553 bytes	8.5%
Joint Photo Experts Group (JPEG), 100% Quality			16,031 bytes	24.4%