PNG's, alphadata and maskdata

[David Bovill]

I'm chopping up a some png's that have transparent backgrounds using Rev, by
getting areas of the image using the imagedata, creating new images and then
exporting these cut-outs. I've got a few questions about images, masks and
alpha channels:

   - To re-create a PNG - do I ned to worry about maskdata - or just copy
   over the imagedata and the alphadata then export?
   - Which of the image file formats supported by Rev support alphadata?
   - Is maskdata used as a part of any image format?
   - What happens when I apply maskdata or alphadata to images displayed in
   Rev that do not support these features?

I'm working on these questions now - so I'll try to answer some of them as I
go along :)