[argyllcms] Fluorescent patches in a profile target?

  • From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 18 Mar 2010 20:22:56 -0700

I'm still working on a less-un-ideal target for profiling cameras, and I've 
been thinking about things a lot.

I've recently realized, in one of those mind-twisting kinds of ways, just how 
many things in a typical photographic scene are likely to be brighter than a 
100% reflective target (such as the Tyvek I discovered or the PTFE that Ernst 
is collecting data on). Of course, there're emissive objects and specular 
reflections...but there're also fluorescent objects. Some cheap office papers, 
for example, have OBAs that push the short-wavelength brightness well over 
100%. I haven't gone searching for any DayGlo things to check, but it wouldn't 
surprise me if some of them have peaks over 100% (at different wavelengths, of 
course) as well.

Adobe Camera Raw, with its flattest settings and the ``Camera Faithful'' color 
profile is actually a not-too-miserable colorimetric match for a scene, 
provided you start with a correct incident exposure and apply the proper white 
balance. The caveat is that a 100% white target will get rendered as L* = 90 
(or thereabouts) and the rest of the highlights will be scaled accordingly. I 
haven't tried to determine the shape of the curve; instead, I've just been 
using the results as a starting point to feed to Argyll.

I'm therefore wondering about the wisdom of including fluorescent patches in a 
profile target in an attempt to characterize the 100%+ range.

Obviously, different lighting conditions will produce different amounts of 
fluorescence. I mainly intend to use this target with studio strobes, which I 
hope have a similar enough spectrum to the illumination source in an i1 to 
produce useful results.

But I'm also wondering about how well Argyll would deal with the math...as well 
as, of course, whether or not it's even a good idea in the first place. And, if 
it *is* a good idea, what kinds of fluorescent materials to look for....

Thanks,

b&

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