A lot of web design I’m involved with these days involves either animating images over backgrounds, or creating composite layouts made up of multiple layered images. These techniques require placing images over one another, and blending the images (usually with shadows) together. This approach requires images with something called alpha (partial) transparency. The alpha channel is a separate stream of data that specifies the level of transparency for each pixel in the image. In web browsers this functionality is available as a 24 bit .png, with 8 bits each for alpha, red, green and blue.
Now for the kicker. Alpha transparency isn’t available in IE6, and unfortunately as I write this, corporate customers still dictate that we support Microsoft’s finest browser creation.
As has been documented for some time, certain workarounds exist for displaying transparent images in IE6. Firstly, the original sleight method used the proprietary alpha image loader filter, and then variations to allow for background images and css – such as supersleight and Angus Turnbull’s png fix – appeared as web 2.0 took off and we started to make more handsome and detailed web pages.
A recent discussion with a work collegue highlighted one major flaw with this approach – the alpha image loader does not support background-position – and as every decent front-end developer knows, you can’t sprite images without this bit of handy css. I’ve also recently discovered that according to Stoyan Stefanov at Yahoo!, the alpha image loader is in fact also very bad for performance.
With IE6 usage down to as little as < 5%, perhaps we don't have to wait much longer to leave these dirty little hacks behind us.