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I have just seen that Wang Imaging and ACDSee do not handle properly TIFF
palettes when all r,g,b values are less than 256. As we know, TIFF palette
is saved by using uint16 entries, but reader is responsible to check whether
the entries are 0-256 or really 0-64K (in which case their values are
"expected" to be divided by 256). Apparently, they always shift them 8 bits
to the right, and thus they get a completely black palette. Photoshop, of
course, does it correct.

Rule of thumb: When saving the TIFF palette image, always save the r,g,b
values (<256) as shifted 8 bits to the left.

Ivo


AWARE [SYSTEMS]		Imaging expertise for the Delphi developer
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	LibTiff Mailing List TIFF and LibTiff Mailing List Archive March 2000 Previous Thread Next Thread Previous by Thread Next by Thread Previous by Date Next by Date Contact The TIFF Mailing List Homepage This list is run by Frank Warmerdam Archive maintained by AWare Systems	Thread 2000.03.30 11:14 "On 16 bit TIFF palette", by Ivo Penzar 2000.03.30 11:37 "Re: On 16 bit TIFF palette", by Peter Nielsen 2000.03.30 17:38 "Re: On 16 bit TIFF palette", by Phillip Crews 2000.03.30 11:14 "On 16 bit TIFF palette", by Ivo Penzar I have just seen that Wang Imaging and ACDSee do not handle properly TIFF palettes when all r,g,b values are less than 256. As we know, TIFF palette is saved by using uint16 entries, but reader is responsible to check whether the entries are 0-256 or really 0-64K (in which case their values are "expected" to be divided by 256). Apparently, they always shift them 8 bits to the right, and thus they get a completely black palette. Photoshop, of course, does it correct. Rule of thumb: When saving the TIFF palette image, always save the r,g,b values (<256) as shifted 8 bits to the left. Ivo

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2000.03.30 11:14 "On 16 bit TIFF palette", by Ivo Penzar