For photographic style images, a JPEG+mask is about half the size of a PNG, much less for very large images. You could just manage your images and masks as sepa

For photographic style images, a JPEG+mask is about half the size of a PNG, much less for very large images. You could just manage your images and masks as separate images, but that carries the cost of an extra GET and possibly misplacing one part. In my case I have a large number of masked, photographic images which need to be in the 300ppi range to manage on a single page and the GETs and file size savings are a clear win. Note: The canvas method works in Firefox, but not for everyone. I'll have to find an afflicted version and see what is wrong. IE should work with FlashCanvas, but I don't have an IE to test with and fear I left something important out of the example at http://blog.jackadam.net/2010/alpha-jpegs/ http://blog.jackadam.net/2010/alpha-jpegs/