[argyllcms] Re: The different color temperatures: questions

On Wednesday 15 April 2009 08:39:47 am Roger wrote:
> Leonard,
>
> You may not have achieved a Zero dE but I'm sure you were very close, well
> under 2 DE. I can't remember how dispcal calculate the DE relative to what,
> but DE relative to target chromaticities is all that matters, if you ask
> me. D50 = 0.3457, 0.3585. If you get close to these numbers (if you aim for
> D50), then you're home free. Because, by definition, you will also have
> achieved 5000K. So the DE number should be ridiculously small. I have a
> Samsung 2693HM here. We must have similar RGB controls.
>
> Roger

I have a Sunsung 245BW and I have played with the controls on it extensively 
while measuring what the controls actually do.  The RGB controls on this 
monitor have almost no affect on the white point of the monitor unless I set 
them to totally crazy settings and even then they only have a slight affect on 
the white point.  I have also done some of the same testing on a few other 
Sansung LCD monitors with similar results.  The RGB controls are much closer 
to gamma controls for each individual channel and primarily affect the gray 
and black color balance.  In addition my monitor has a native white balance of 
about 6600K which is so close to the normally recommended 6500K that I don't 
think there is any reason to be concerned about the difference particularly 
since it can't be adjusted without using settings that are completely off the 
wall.  So what I do is set Argyll to native white point and then use the RGB 
controls to adjust the overall gamma and the systems black point to get the 
gamma as close as possible to my target and to get the black point close to 
the native white point of the monitor.   At least for my monitor this work 
nicely.  But your controls could function in a totally different way and you 
might need a very different approach to make things work for your monitor.

My point is that just because software like Argyll has facilities to help you 
adjust various monitor parameters like white point does not mean that it is 
possible to actually adjust any one of these for any particular monitor.  In 
addition in at least some cases making these adjustments to your monitor 
without understand how the particular controls you are adjusting actually 
behave may actually give poorer results than leaving the controls set to 
factory defaults.  

So the first thing you need to do is to figure out what the various controls 
actually do.  My experience with LCDs is that the markings on the controls are 
in may cases meaningless and have nothing to do with what users who are trying 
to use calorimetry would expect from controls with those names.  For example 
on a CRT we expect a set of RGB controls that allow us to set the devices 
white point yet on my LCD these controls are actually per-channel gamma 
controls and have virtually no affect on white point. The controls on CRTs all 
operate in the same manor on all CRT monitors no matter who the vendor is 
although there may be differences in how these are labeled from vendor to 
vendor and how many controls are exposed to the user.  The reason for this 
consistency is that these controls are directly related to how the device 
actually works and are actually adjusting various analog hardware components.  
This consistency makes it relatively simple for someone to write up 
documentation about how to use these controls with calibration software (like 
Argyll for example) to get the correct results.   

Unfortunately for LCD monitors this is not the case.  The controls have no 
direct relationship to how the hardware actually operates.  And how the 
hardware operates is also completely different from a CRT.  As a result there 
is almost no consistency for what controls are available and what these 
controls actually do from vendor to vendor and perhaps even model to model 
from the same vendor.  The only exception is the back lite brightness control 
and again this is related to the fact that this is a control that directly 
alters a setting on an analog device in the LCD. 

>
> > I was never able to achieve a zero DE to locus for any of the four
> > possibilities with my Samsung 226CW.   I made numerous attempts
> > incluing
> > several of which involved adjusting the RGB settings.

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