Massimo Colagrande wrote:
It took me sometime to understand that despite the results on the
ColorChecker SG
looked better, some colors outside the chart may be strongly deviated while
creating
XYZ cLUT profiles.
Let me resume my findings: a.. Scanner ICC profile created using “XYZ cLUT”
setting on
a referenced ColorChecker SG: Lowest DeltaE on ColorChecker SG patches, strong
deviations on some colors outside the ColorChecker SG with some
posterizations and
colors drastically changing hue (some yellow become green and so on). Results
may
changes drammatically if for example there is a slight change in the
reference LAB
values of some color patches or using a different ColorChecker SG. b..
Scanner ICC
profile created using “LAB cLUT” setting on a referenced ColorChecker SG: Low
DeltaE on
ColorChecker SG patches, medium deviation on some colors outside the
ColorChecker SG
(red cast on some colors). c.. Scanner ICC profile created using “Gamma
Matrix” setting
on a referenced ColorChecker SG: Higher DeltaE on ColorChecker SG patches,
but more
respectfull of colors outside the ColorChecker SG. While my findings are not
definitive
it seem that the “Gamma Matrix” (as suggested by Graeme) provide the smoother
results
and therefore the best compromize in my opinion. “LAB cLUT” is more accurate
on some
colors but worst on others. “XYZ cLUT” have strange behaviour on some colors
and is
therefore unsuitable in my case.
And now some other considerations, I tought that adding more colors to the
profile
(colors that are needed but are not in the ColorChecker SG) could solve the
issue
allowing to build a more accurate “LAB cLUT” or even “XYZ cLUT” profile...
The results clearly show some sort of uncompatibility between the
ColorChecker SG chart
and the “custom patches” from the RAL chart. While the added colors improve
drammatically in the new profile, some other color, even patches on the
ColorChecker SG
start showing posterizations (even in the neutral patches).
I’m therefore struggling on the attempt of understanding: a.. why the 2 color
patches
from the 2 charts cannot be used together, is there a simple or complicated
answer to
this ?