Elle Stone wrote:
An issue with camera matrix profiles made with v1.0.4 was that the brightest patch got scaled to L=100, for reasons that make sense for a printer profile but not so much for a camera profile.
you are right IMHO -- it doesn't make much sense for me either. But it is the "expected" behavior for an ICC compliant input (i.e scanner or camera) profile.
[...] I had an idea when working with v1.0.4. The idea was to add two artificial data sets to the ti3 file before using colprof. One data set was for perfect white, L=100,a=b=0 and one was for perfect black, L=0,a=b=0: GS0B 0.00000 0.00000 0.00000 0.00000 0.00000 0.0000 0.1 0.1 0.1 GS0W 96.420 100.000 82.491 100 100 100 0.5 0.5 0.5
I did/do something similar for scanner profiles routinely, but instead of assuming R=G=B=Y=0 and R=G=B=Y=100, I use data extrapolated from gray ramps or preliminary profiles (I extrapolate the gray ramp until one of the values for R, G, B or Y reaches 0 or 100)
As you can see from the "peak err" and "avg err" reports, adding the artificial data sets decreased errors.
I've noticed this effect often (but not always).
Also, what might not be so obvious, is that the profile made with the artificial data sets is color-balanced, meaning r=g=b=neutral gray.
Yes, but this might be misleading if the actual device response is different (e.g. due to offset or white balance errors).
Can anyone see a problem with this "trick" of adding artificial perfect black and white data sets to the ti3 file before running colprof? Or maybe it's something people already do that I didn't know about?
see above. Klaus
