[argyllcms] The right way for device input profiles and artificial light sources?
- From: Stephen T <stwebvanuatu@xxxxxxxxxxxx>
- To: Argyll CMS <argyllcms@xxxxxxxxxxxxx>
- Date: Tue, 3 Dec 2013 04:26:58 -0800 (PST)
Hello,
I have been playing around with camera profiles for tungsten and fluorescent
lighting.
As I understand, there are 2 things that happen when the light source changes:
1) Device RGB changes (what the camera sees).
2) XYZ changes (what the standard observer sees).
I have made simple matrix profiles. There are 3 different profiling strategies
I have tried:
1) Profile with D50 reference data (ignore changes in XYZ).
2) Profile with XYZ computed for the CIE illuminant most closely matching the
light source (non-standard profile white point).
3) Take XYZ from step 2 and perform a chromatic adaptation transform to D50
(standard PCS white point).
Which of these is recommended?
Profiling errors with the 3 different XYZ are similar (a good fit doesn't mean
the results will be sensible in practice however). Options 2 and 3 produce
exactly the same rXYZ, gXYZ and bXYZ, only the WTPT is different. Options 2 and
3 produce identical images in my workflow and I guess the non-standard white
for option 2 is being accounted for?
For real photos in warm light, I have found all 3 tungsten profiles are
similar. The D50 reference data produces slightly warmer reds.
There are greater differences in photos with fluorescent lighting, where the
D50 reference data produces a warmer, more pleasing image. Options 2 and 3 look
a bit greenish. Perhaps this is because I profiled with a light source
approximating F5 daylight and the test photos were shot with inferior, lower
colour temperature lights?
Compared to daylight profiles, the artificial light profiles do produce more
realistic colours. I haven't done any quantitative tests yet.
It's strange that the D50 reference data seem to be useable, as the colorimetry
of the target does change and the rXYZ, gXYZ, bXYZ tags can be very different.
Here are some colour differences I calculated after CAT:
Mean DE94 between D50 and illuminant A after CAT to D50 = 1.5.
Mean DE94 between D50 and illuminant F5 after CAT to D50 = 2.4.
Appreciate any tips, advice.
Stephen.
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