While I was writing my previous post on ImageOptim (a free Mac application for reducing PNG file size), I came across a fascinating article about the PNG format, written by Kornel Lesinski, the author of ImageOptim.
His article outlines the tools needed to create 8-bit PNG files that have a full alpha channel, resulting in huge file size savings if you are willing to sacrifice a small amount of quality be palletising the image. This format is supported natively by Adobe Fireworks, but for those of us stuck using Photoshop, Kornel has even created a free Mac OS application, ImageAlpha, which can convert 24-bit PNG files to this format.
I’ve just performed a quick test on a transparent PNG file, and the combination of ImageAlpha and ImageOptim reduced the file size from 11108 bytes to 2775 bytes, a saving of a whopping 75%. This obviously isn’t an exhaustive test, but it’s a very promising start, and I’m looking forward to letting these tools loose on the images for my new website.