[argyllcms] Explain what happened

  • From: Leonard Evens <len@xxxxxxxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 02 Dec 2008 14:02:35 -0600

As I noted previously, I've returned to color management after a time
away from it.   I thought I was up to speed again, but something
happened that seems to contradict what I thought I had understood.

I recently got a Dell laptop running ubuntu 8.04.   I installed the
argyllcms programs and tried to use dispcal to calibrate/profile its

I used
dispcal -v -yl -0 TargetA
with an Eye-One LT
I ignored the first set of numbered instructions because there are no
controls that I can adjust---which may have been a mistake---, and I
went directly to the last two steps: the check of ambient light and
making the profile.  It did produce a profile TargetA.icc.

I assumed on the basis of what I thought I  understood that the
calibration part, i.e., loading the video LUT was irrelevant and that
the profile would be made under the assumption that it would do all the
work.   I then told gimp that TargetA.icc was the monitor profile.  But
that had no effect whatsoever on the colors that gimp put on the screen
in an image window.  So I tried
xcalib TargetA.icc
and that immediately turned the background (which I had previously set
to R 128, G 128, B 128) to neutral gray.  (Before it has been the bluish
gray you sometimes get on un calibrated laptops.)  In other words a LUT
was in fact loaded in the video card.

So I clearly don't really understand the distinction between calibrating
and profiling.   And I don't really understand what gimp color
management is doing.   I thought I had a good understanding of all that,
but I was wrong.

As well as an explanation, some suggestions of various experiments I
could try might be helpful.

Leonard Evens <len@xxxxxxxxxxxxxxxxxxxxx>
Mathematics Department, Northwestern University

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