AWARE SYSTEMS
TIFF and LibTiff Mail List Archive

Thread

2004.05.20 11:05 "[Tiff] Extra samples handling", by Mayank
2004.05.20 23:42 "Re: [Tiff] Extra samples handling", by Chris Cox
2004.05.21 09:05 "Re: [Tiff] Extra samples handling", by Mayank
2004.05.21 19:22 "Re: [Tiff] Extra samples handling", by Chris Cox
2004.05.21 12:00 "[Tiff] Un-premultiplying the color data", by Mayank
2004.05.21 19:30 "[Tiff] Re: Un-premultiplying the color data", by Chris Cox

2004.05.21 19:22 "Re: [Tiff] Extra samples handling", by Chris Cox

i still have this doubt whether multiple associated alpha channels are possible? if yes, the how do you un-premultiply the color values, for each of the associated alpha channels?

Multiple associated alphas are possible in theory - and there are no guidelines for how to handle that case.

I suspect it would depend on the application that generated the file, and what it intended the extra associated alpha channels to do (act as additional masks, or act as additional transparency). This boils down to: do you screen or multiply the associated alphas to create a final alpha?

Chris