[argyllcms] Re: The different color temperatures: questions
- From: "Hal V. Engel" <hvengel@xxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 15 Apr 2009 10:55:21 -0700
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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