1994.09.20 03:03 "TIFF CIEL*a*b* Question (with Answer)", by John M
Davison
Thread
1994.09.20 07:53 "Re: TIFF CIEL*a*b* Question (with Answer)", by Fredrik Lundh
It would seem, then, that Compression values of 2 (CCITT Group 3 1-Dimensional Modified Huffman run-length encoding), 3 (T4-encoding), and 4 (T6-encoding) are acceptable only for images in which all of the following conditions are satisfied:
- BitsPerSample[0] is equal to 1.
- PhotometricInterpretation is 0 or 1.
- m = (number of ExtraSamples) is equal to SamplesPerPixel minus 1.
You could use m > 1 and PlanarConfiguration=2, and why not PhotometricInterpretation=3.
But don't ship such files outside your office... When using Compression=3 or 4, I'd stick to SamplesPerPixel=1, PhotometricInterpretation=0, and RowsPerStrip=ImageLength!
I believe things like the CCITT encodings (especially T4/T6), JPEG, and (even) colour separations are _accommodated_ by the TIFF-spec, not defined by it. The idea of putting them into the TIFF-spec is to allow people to use TIFF mechanisms for adding image descriptions, put multiple images in a single file, etc; not to tweak the original standard.
/F