PS7, PNG and alpha channels

[Dave Hodgson]

How can I get alpha channels to save with PNG files?

I tried using SuperPNG, the free plug-in, but it won't save alpha data either. Are there any other plug-ins that will save alpha channel data?

I don't want to save a transparency mask or any other kind of PS specific transparency, I specifically need the 8-bit alpha channel to be stored in the file.

[Trevor Morris]

As you've discovered, Photoshop is not capable of saving an 8-bit RGBA PNG - not even with SuperPNG. You will either have to use another application, or use PNGQuant ([url]http://www.libpng.org/pub/png/apps/pngquant.html[/url]).

[Dave Hodgson]

Actually, it is. I found out that in order to save alpha data in a PNG file from photoshop, you have to use layers not alpha channels. If you leave the bottom layer empty so that all the transparent areas show through as the checkerboard, then SuperPNG will save the empty areas as alpha value transparency,

[Trevor Morris]

Chris,

Not in 8-bit (i.e. 256 colors): however, what you say is correct for 8-bpc.

Oh, and I just reread the original post and see that Dave did not ask about 8-bit files, but rather 8-bit alpha channel. So, while (I believe) everything I said is correct, it appears that it was out of context :-).

[Trevor Morris]

Fair enough, understood Chris. In fact, the emails we've exchanged have really helped clarify this point. Thanks for the reminder ;-).