[argyllcms] Re: The different color temperatures: questions

On Wed, 2009-04-15 at 10:55 -0700, Hal V. Engel wrote:
> 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. 

I don't think I understand that statement.  Is there a typo in it?



>   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.

What you say describes pretty well my experience with the Samsung 226CW.
I was never able to conceptualize what the monitor controls were
supposed to be doing.   Also your comment that the RGB controls may
explain why I kept ending up with color tints to grays.

I was never able to figure out even what the Brightness and Contrast
controls were doing, and which to use at which stage when trying to use
dispcal.  I suspect for this monitor that the light source was constant
and not adjustable and all the controls just adjusted the internal LUT
in the monitor, but how seemed rather mysterious.

I am hoping to find it easier working with the XL20 which is an LED
monitor.
At least it is designed to be calibrated/profiled.  But the 226CW works
fine for my wife who can make use of the wide screen format.

>  
> 
> >
> > > 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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