PNG 8-bit + 4-bit alpha

png alpha

[KenNashua]

I have a bunch of 32-bit png graphics which I need to crunch down to save space. I'd like to convert these to 8-bit indexed color with an additional 4-bit alpha channel, but I can't seem to find any programs which will actually support this combination. Anything which indexes it seems to either eliminate the alpha channel or reduce it to a single color.

Anyone have any pointers to programs I could use (batch support would be preferable).

[kingkelly]

Finally a good topic!

8-bit PNG is pretty much greyscale...
I do believe PNG's transparency is limited to 3 choices: Alpha channel, 1 color, or no transparency at all. You'll prolly have to settle with crunching the PNGs down to 8-bit with alpha channel.

Limitting the transparency on PNGs does NOT always make the size smaller. Depending on the dimensions, and your alpha channel, turning the transparency to 1 color instead of using the entire alpha channel sometimes makes the size bigger...

Cheers

[waldemar]

Ken:
Sorry, don't know about a program supporting 8bit + 4bit alpha either. Actually I had a hard time finding a good software for good png export at all...

Still, I recommend trying out Uleads SmartSaver (trial version runs like 2 weeks) for very good compression results and lots of options to choose from (all filters, etc.) - leaving enough room to experiment with different compression results. However when switching from tue color to indexed the alpha channel option is disabled here as well (limitting transparency to one color). :-(

[kingkelly]

PSP has an awesome export feature that lets you compare the optimised to the original before saving. You can adjust all the transparency, and colour depths. And it tells you the updated new size....