1997.01.09 16:23 "Re: BITSPERSAMPLE question", by Tom Lane
From what I understand of the TIFF 6.0 spec (pg. 28-29), a TIFF implementation should be able to cope with different bit depths for every channel.
The spec allows such images to be represented, but it does not require TIFF readers to handle them. (Note that all flavors of baseline TIFF have equal bitspersample for each channel.) This is one of many optional features of TIFF.
After looking at the sources, I think that libtiff doesn't allow this.
Correct, libtiff is not designed to support this. AFAIK, Sam has no plans to improve libtiff in that particular direction. Such images are very few and far between.
regards, tom lane