[argyllcms] Re: Gamma wrong for calibration curves?

>Ah, well, I think what you've noticed is that between the...

Graeme,

I did some further testing.  I copied the 3 bitmap screens that dispcal
uses to calibrate the screen and put them in a directory where I could
switch between them quickly using ACDSee.  Then I ran 3 calibration checks
(dispcal -r) using the bitmaps as displayed by ACDSee rather than the ones
displayed by dispcal.  To prevent dispcal from modifying the laptop display
LUT I set my laptop screen up as a secondary monitor to my office LCD
screen, and told dispcal to display on the office LCD - so dispcal modified
the LUT for the office LCD and the laptop screen retained any LUT entries
it had had while dispcal made the readings off the bitmaps as displayed by
ACDSee on the laptop screen.   :-)

Below are 3 of these modified dispcal tests that I ran.  The first is with
no calibration or profile applied and matches what dispcal would report if
run normally on the laptop screen.  The second run is with the original
dispcal-produced LUT loaded.  The third is with the LUT loaded and the
profile (created by "profile") applied (via ACDSee).

The interesting finding is that the laptop screen with no LUT has a gamma
of 2.24, with the LUT only applied the gamma is 2.03, and with both the LUT
and the profile applied the gamma is 2.24 again!  This seems to indicate
that dispcal is creating a calibration curve with a low gamma and then
"profile" is compensating and setting the gamma higher again.

- Bill

No calibration or profile applied:
I:\Util\Argyll\profiles>..\bin\dispcal -v -d1 -yl -r -p .5,.5,1.25
Setting up the instrument
Place instrument on test window.
Hit Esc to give up, any other key to continue:
patch 3 of 3
Black level = 0.30 cd/m^2
White level = 134.01 cd/m^2
Aprox. gamma = 2.24
Contrast ratio = 447:1
White chromaticity coordinates 0.3289, 0.3517
White    Correlated Color Temperature = 5651K, DE to locus =  9.0
White Correlated Daylight Temperature = 5651K, DE to locus =  5.3
White        Visual Color Temperature = 5410K, DE to locus =  8.7
White     Visual Daylight Temperature = 5522K, DE to locus =  5.1
The instrument can be removed from the screen.

Calibration only applied:
I:\Util\Argyll\profiles>..\bin\dispcal -v -d1 -yl -r -p .5,.5,1.25
Setting up the instrument
Place instrument on test window.
Hit Esc to give up, any other key to continue:
patch 3 of 3
Black level = 0.30 cd/m^2
White level = 134.22 cd/m^2
Aprox. gamma = 2.03
Contrast ratio = 447:1
White chromaticity coordinates 0.3291, 0.3518
White    Correlated Color Temperature = 5643K, DE to locus =  8.9
White Correlated Daylight Temperature = 5644K, DE to locus =  5.3
White        Visual Color Temperature = 5404K, DE to locus =  8.7
White     Visual Daylight Temperature = 5517K, DE to locus =  5.1
The instrument can be removed from the screen.

Calibration and profile applied:
I:\Util\Argyll\profiles>..\bin\dispcal -v -d1 -yl -r -p .5,.5,1.25
Setting up the instrument
Place instrument on test window.
Hit Esc to give up, any other key to continue:
patch 3 of 3
Black level = 0.58 cd/m^2
White level = 133.72 cd/m^2
Aprox. gamma = 2.24
Contrast ratio = 231:1
White chromaticity coordinates 0.3282, 0.3518
White    Correlated Color Temperature = 5678K, DE to locus =  9.3
White Correlated Daylight Temperature = 5678K, DE to locus =  5.7
White        Visual Color Temperature = 5425K, DE to locus =  9.0
White     Visual Daylight Temperature = 5538K, DE to locus =  5.5
The instrument can be removed from the screen.

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