Hello Dave,
Thank you. I'm happy PixInsight LE can be useful for you.
You can rest assured that PixInsight's TIFF support is 100% compliant with the TIFF 6.0 specification. This is guaranteed by the fact that our TIFF routines are based on LIBTIFF software library by Sam Leffler at Silicon Graphics.
It could be that the file you're trying to load has been incorrectly generated. One of the most frequent errors is lack of adequate TIFF tags to describe a RGB image properly. Could you please send me one of these TIFF files?
It's just amazing how many poor implementations are out there, especially considering that TIFF and FITS are two wonderfully documented formats.
I guess from your second message that you've already discovered the ImportChannels process of PixInsight LE. This process is quite rough, actually, but it works well to composite separate RGB channels. Using this process is quite straightforward; let me know if you need more info.
The next version, which will be the first public release of PixInsight Standard, will have image registration processes (manual, semi-automatic, and automatic registration), as well as a sophisticated channel merging/splitting process, including Fourier-based channel registration with subpixel accuracy.
There will be also a dynamic process implementing complex layered compositions. I cannot say more about this process, but it will be a very sophisticated and "surprising" thing for sure.
Thank you for using PixInsight LE.
Best,