YAMAMOTO Mitsuharu wrote:

> At least, your patch misses the case of non-paletted transparent PNGs
> (tb???c?? in http://www.schaik.com/pngsuite2011/pngsuite_trn_png.html).

Thanks for catching my mistake. I installed the attached patch, which is closer 
to the code you originally suggested. With it, displaying one of the images you 
suggested looks like the attached image; hope it's what you're looking for. (I 
disabled font-lock-mode as you also suggested.)