2002.07.04 16:01 "Re: Photometric interpretation for grey-scale JPEG", by Jon Saxton
** Reply to message from Tom Lane <firstname.lastname@example.org> on Thu, 04 Jul 2002 01:13:50 -0400
Is this correct? If so, then should 6 be an acceptable PI for grey JPEG-in-TIFF?
Absolutely NOT, imho. 1 (MINISBLACK) is correct for grayscale JPEGs.
The fact that you came across some cluelessly encoded TIFFs is not grounds for breaking such basic assumptions as that PhotometricInterpretation has something to do with the colorspace of the stored data.
The only reason TTN#2 doesn't spell this out in so many words is that it never occurred to me that anyone might think otherwise.
Ouch! I guess I have been told. But that was the point of asking anyway.
Now, I have a follow-on question. How is it that PhotometricInterpretation has nothing to do with the colour space of the stored data? In the section headed "What data is being compressed?", TTN#2 says:
>... Therefore, if color conversion or downsampling are used, > they must be reflected in the regular TIFF fields; these steps
> are not considered to be implicit in the JPEG compression tag > value. PhotometricInterpretation and related fields shall
> describe the color space actually stored in the file.
What part of the last sentence don't I understand?
Jon Saxton <email@example.com> Software developer for UNIX, OS/2 and Windows
U.S. agent for Triton Technologies International Ltd