I thought you were using something like a low (2,3,4) bit PNG with a cmap. If there's no cmap then the suggestion is rather pointless.

Would you be able to write the less efficiently packed file faster than the one you're writing now? Would the browser display it faster than the one you have now? I don't know if you've compared the sizes/times. My player is sitting around doing a disk check right now so I can't go look at the file myself (you didn't break the disk check pref in the latest hijack did you?) Emplode has been going for what seems like an eternity (completed one whole progress bar and now it's going again...)

Bruno