[argyllcms] Re: "gamma key" Re: Photocamera calibration questions
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Tue, 24 May 2011 08:41:57 +1000
yan@xxxxxxxxxxxxxxxxx wrote:
When you write "by hand" you mean, that I
need to write another tool by myself. Of course, it's kind of an aswer
:-) But this is rather hard thing. And, on the other hand, I think that
only slighter code changes are needed.
There are several paths available to you. You could code it
in C using (Argyll) icclib. You could probably do it even
easier using lcms, and lcms may have scripting interfaces available
if you want to use something other than C (ie. lcms-python, tcllcms etc.).
Coolproof in matrix+gamma
mode reads ".ti3" values and try to
1. Guess gamma values;
No, it doesn't do any guessing. If fits a response
curve to the device behaviour exemplified by the .ti3 data points.
The only key I need is "not to guess gamma
upon ti3 values, and assume gamma is [some value]". The linearity of
camera sensor is quite a good assumption. By analizing this or that real
data you get "gamma 2.18" or "gamma 2.21", and this number would be not
exactly 2.2 only beacause of camera noise.
This is what I mean by colprof not being the ideal tool. It fits
the profile to the data as given, using a least squares type
fit criteria.
One workaround would be to process your data values to be
linear light and then use the -am option to fit the matrix only. You
would then have to patch the profile and change the gamma value
in the R,G & B curve tags to be the gamma you know it to be.
Graeme Gill.
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