spencehg1

Thanks for the suggestion. Unfortunately there are multiple issues. This work is being done by an internally funded volunteer 501(c3) group. We have already pushed our economic limits and the generosity of our team members. Buying a spectrophotometer that probably will not do what we need is not a viable option. I have not been able to find one locally that I can borrow for a test.
The subjects are ancient cliff face pictographs that vary from 800 to 6000 years old. Using a contact spectrophotometer is out of the question. I have been told that the variable reflectivity and calibration issues with each of many samples being rephotographed every 3 to 6 months makes their use problematic if not impossible.
If anyone knows of a spectrophotometer anywhere near Sedona, Arizona that I could use to test a couple of samples (I do have some "portable" examples) I would be willing to try.
Basically what we have learned is that using a Macbeth card to calibrate camera and light source to get "accurate" colors is relative at best. It appears that we have overestimated and become over-reliant on the capabilities of this specific methodology.
Thanks again.

Strodav Loc: Houston, Tx

That's why I recommended a non-contact spectrophotometer, but if that's not an option, you will have to solve the variability in light problem to use a camera. Maybe the way to go is to use a calibrated light meter (less expensive than a spectrophotometer) to ensure repeatibility in both intensity and color temperature of the lighting. You can work on the profile issue once you are sure the lighting is consistent.