1999.07.16 19:40 "RE: RGB Gradient Code, adapted from Andreas Neumann (sol'n)", by Eric B. Middlecamp
I _know_ from some discussion on comp.graphics.apps.photoshop that PS does fiddle with your data WHEN THE DEPTH OF EACH BAND IS GREATER THAN 8bits and it must be converted for display. They do some random dithering that is not really documented well, but the prepress people like.
In your case, I know that you have 8bit bands, so the above does not come into play. However, given the above, it seems reasonable that PS is doing something and they are not telling you the truth about your image. I think the problem is in PS, not LibTIFF...
Actually, I now seem to remember some folks talking about only having 7bits per band of "true" data in PS. Don't remember the specifics of that though.... Talk to Adobe...
I've found the culprit, and as it turns out it could be potentially embarrasing, so.. go easy on me. In Photoshop, under profile setup, there was a default ("dont ask") conversion in place for RGB images. Having removed this, everything is as it should be. Sigh.
Many thanks for the feedback,