[argyllcms] Re: Contrast vs Brightness on my LCD monitor and related questions

On Sat, 2008-12-06 at 17:15 +1100, Graeme Gill wrote:
> Leonard Evens wrote:
> > One thing that confuses me is that by appropriate choice of the default
> > gamma setting---the monitor offers 3 possible settings, dispcal -r shows
> > gamma = 2.2., but after calibrating/profiling and loading the
> > calibration into the video LUT via xcalib, I get quite high gammas, in
> > the range 2.6 to 3.1.  I've even tried using the argument -g 2.2, but
> > that doesn't seem to make any difference..
> 
> Gamma is hard to measure, because no-one can agree on
> exactly what it is. If you use ambient light adjustment,
> then the gamma may be boosted to increase the contrast.

This seems to be the issue.  If I don't use the ambient light
adjustment, I get something close to the target gamma.

I am using a Eye-One LT, and for ambient light measurement, I clip on
the white plastic cover, which I believe is supposed to be used fro that
purpose with the Eye-One software under Windows.  But perhaps that is
confusing matters.  I also have an Eye-One Pro, which may do a better
job with ambient light measurement.

But I'm not sure at this point whether or not I should be using the
ambient light measurement at all.  When I calibrated/profiled this same
monitor last year---I thought successfully---with version 0.8, there was
no ambient light option.

On another point, whatever I do, I always get a message like

Failed to meet target 0.600000 delta E, got worst case 0.607690

with different worst cases.

Does this mean anything?

> 
> Normally the "dispcal -r" report should agree reasonably
> with the target set using -g, if ambient compensation is
> not being used.

As I said, it does if I don't use the ambient light option.  According
to the `Amazing Gamma Applet', gamma seems to be between 2.1 and 2.4.

I still feel I am having difficulties because I don't understand hwo to
use Brightness and Contrast in the monitor controls.   Also, with the
RGB monitor controls set at the default 50/100, I am getting lower color
temperatures than I would prefer.  I will experiment some more with the
controls and also try setting the color temperature.



> 
> Graeme Gill.


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