2004.01.23 19:19 "Re: [Tiff] How to convert MINISBLACK to PHOTOMETRIC_RGB", by Bob Friesenhahn
I am by no means an authority on the TIFF specification. My interpretation of the file in question is that a sensible application should render the first band in greyscale and ignore the 2nd and 3rd since they are extra samples with no meaning attached. Without the ExtraSamples tag, I think an application should assume the file contains 3 greyscale bands which might be drawn in any number of ways. One way would be to draw 1 band, and give the user the ability to flip through to see the 2nd and 3rd. Another would be to just treat them as RGB (as many multispetral imaging packages will do with the first 3 bands of multispectral data).
I am no TIFF authority either. I aggree with your summary. The extra samples could mean almost anything. More than likely the correct intepretation of the extra samples depends on the vendor extension tags that libtiff warned about. :-)