2007.08.06 22:48 "RE: [Tiff] Transparency ... associated or unassociated alpha is morecompatible?", by Bob Friesenhahn

PNG and SGI RGB support associated alpha (aka transparency), just not premultiplied.

Thanks for correcting my wrong use of terms. It is a pity that TIFF does not provide a way to specify associated alpha which is not premultiplied.

TGA is supposed to support associated alpha (transparency), but most

users of TGA don't seem to understand the difference and get

transparency and general (unassociated) alpha channels confused.

When Photoshop 7 shipped with transparency support in TGA format,
got so confused that Adobe had to go back to using the users

> unassociated alpha. The TGA users still can't agree on what they > want, much less what they understand.

That is interesting to know. As far as I am aware, GraphicsMagick handles alpha correctly (according to written specification) for TGA files. I spent quite a bit of time double checking it and fixing things.

Bob
======================================
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/