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Posted by Bob Myers on 11/07/07 04:16
"Rita Berkowitz" <ritaberk2O04 @aol.com> wrote in message
news:13j2941i4jgfb41@news.supernews.com...
> Of course I'm aware of a CRT being an RGB device. That's the point; it
> generates and projects light in the primary colors. On the other hand an
> LCD can be viewed as a filter that passes or attenuates certain portion of
> the light spectrum at any given instance to produce colors and images.
> Even
> if your claimed white light source, fluorescent in this case, doesn't have
> a
> small portion of the needed color spectrum you will not be able to
> accurately produce the desired color. All "white" light isn't created
> equally, hence the crappy and unsatisfactory results one gets from an LCD.
Sorry, but....you're still wrong. The "white light [not] created equally"
question (whatever you think that means) is not the root cause of
poor color accuracy in LCDs. Again, the primaries are what the
primaries are; if we assume both a CRT display and an LCD with the
same primary set (let's assume the sRGB primaries, since those or
something close to them are all you'll get from a CRT), then the color
gamuts of the two are identical by definition. And further assuming
equally good control over those primaries, you could set the white
points to be identical and produce any color within the gamut to the
same accuracy. The color problems of the typical LCD - and please
note that I agree they exist, in the *typical* LCD - do not result from
the nature of the backlight. (If they did, the CRT would likely suffer
from the same problems; both the CCFL and the CRT are phosphor-
based emitters, and the phosphors are not that dissimilar. Both have
what you are calling a "spiky" spectrum, for instance.)
No, the LCD's color accuracy problems come primarily (not
exclusively, but primarily) from the following sources:
- Inaccurate and inconsistent emulation of the desired tone response
or "gamma curve", including differences in response among the three
primary channels;
- Inaccurate primaries, in terms of the primary color NOT being
at the nominal spec; typical tolerances on these are up to +/- 0.03
in terms of CIE xy coordinates (which, unfortunately, are the way
these things are still specified), and
- Limited dynamic range (number of bits of control per primary;
typically not better than 8 bits/color and often just 6).
Solve these, and you can have an LCD display as color-accurate
as any CRT; in some ways, better, for some applications, as the
LCD is no longer limited to the sRGB or other CRT-like gamuts
(try and find a CRT-based display covering AdobeRGB, for
instance). As of right now, it's very unusual to find an LCD monitor
in which these are fixed - but we're getting to the point in the state
of the art where such things can be done.
Bob M.
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