Fwd: Monitor calibration best practices
Fwd: Monitor calibration best practices
- Subject: Fwd: Monitor calibration best practices
- From: Cdtobie <email@hidden>
- Date: Tue, 14 Oct 2008 22:00:01 -0400
From: Cdtobie <email@hidden>
Date: October 14, 2008 9:57:18 PM EDT
To: Roger Breton <email@hidden>
Subject: Re: Monitor calibration best practices
Actually not all LCDs do have brightness and contrast controls. Some
have both, plus backlight, but many, including most laptops and all
Apple LCDs have no brightness or contrast controls at all; only a
backlight adjustment.
Brightness controls are traditionally used to adjust the blacks to
avoid black clipping. A backlight control won't do that. Contrast
controls were traditionally used to adjust whites to avoid white
clipping; a backlight control won't really do that either. What it
will do is adjust white luminance to a lower level, to better relate
to low ambient or proofing light levels.
Since LCDs don't work like CRTs, simply assuring at the factory that
they are set up to provide appropriate detail at the black and white
ends makes such controls rather unnecessary. But that doesn't leave
the tinkerers of the world much to tinker with...
C. D. Tobie
WW Product Technology Mngr.
Digital Imaging & Home Theater
DataColor.com
email@hidden
On Oct 14, 2008, at 9:21 PM, Roger Breton <email@hidden> wrote:
It may seem silly but I have to admit that I finally understand
what is
meant by 'backlight' -- thank's CD.
Of course, all LCD monitors have Contrast/Crightness controls
otherwise
dubbed "backlight" control on this List.
These Contrast/Brightness controls are not be considered as "true"
separate
hardware Contrast/Brightness controls, the way we found them in the
days of
CRTs but they nevertheless control, at the hardware level, just how
much
light is being emitted (radiated) by the monitor.
Quantization now seems a little clearer in this context.
Please correct me if I am wrong but as long as one dims down the
monitor
through the OSD's Brightness/Contrast controls, otherwise called the
"Backlight" in geek color management parlance, one is not losing
discrete
brightness levels to quantization. Only when one is dimming one or
any
combination of the three channels in the host computer video LUT,
there are
quantization issues. Right?
That's why many regular contributors on this List advocate never
changing
the white point control of an LCD monitor, right? For fear of
introducing
quantization or loss of discrete brightness levels at the video LUT
levels.
But suppose an LCD monitor with useful separate RGB controls. Then
what?
I'll say *if* the white point adjustment can be controlled in
hardware,
suppose from native 9000K down to 5000K or D50, then I think it is
fair to
say that no quantization should ensue as a consequence. Other than
the
slight quantization that would be introduced by calibrating the
individual
channels to obtain a gray ramp (R=G=B=from 0 to 255) to the chosen
white
point chromaticities (Little x/y). There I think it is unavoidable
to have
some slight quantization being introduced as a consequence of
calibrating
the grayscale from the monitor white down through the black point.
The only time that we should be freed from the specter of
quantization is
when the grayscale calibration is carried inside the monitor LUT
itself, as
with the Eizo's, the NEC's, the HP and the Quatto's, leaving the
computer
video LUT untouched (linear).
Is that better?
Roger
Yes, of course I meant lowering the display's brightness using the
display's
own controls, separate from the LUT in the CPU's graphic card.
Marco
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