"Andrew Gabriel" wrote in message
...
In article ,
"Leonard Caillouet" writes:
"Andrew Gabriel" andrew@a20 wrote in message
...
In article ,
"Dave Plowman (News)" writes:
In article ,
William Sommerwerck wrote:
And the same will apply to LED backlights. It's a big con that
LEDs are more efficient -- they only are where supplying narrow-
bandwidth light. As soon as you try and make them produce
continuous-spectrum light -- ie white -- the efficiency goes way
down. Of course, they may improve -- but then again, so may
fluorescent.

White LEDs are not continuous-spectrum. They contain a phosphor that
produces yellow light when stimulated by blue light.

Indeed. So not suitable for where you need a decent quality light. As
for
an LCD backlight.

I don't see why an LCD backlight needs to be anything other than
red green and blue, and having just checked one, that's exactly
what it is -- actually very much narrower bands than a regular
fluorescent, and without any of the other fill-in colours you
get from a fluorescent lamp. After all, anything else from the
backlight would be wasted (or worse, might bleed through into
some colour cells and contaminate the primary additive colours).

Y
That depends on the assumptions you make in the production of the source
and
the decoding to those narrow spectrum RGB displays. You may or may not
end
up with the same distribution of secondary and intermediate colors. The
human eye perceives color over a spectrum approximated by the CIE
standard
observer curves. Concentrating all of the energy at narrow bands can
have
some very significant effects, not only in overall brightness, but in
color
reproduction. While it is true that any color (within a given gamut) can
be
made up of a combination of narrow band RGB display sources, getting the
right spectral power at a given color requires mapping from what the
pickup
and encoding assume to what the display can produce. Unfortunately,
there
are not many good options for measuring response at colors other than
primaries and secondaries and no good standards for evaluating
performance
objectively at this time for intermediate colors, much less for those
colors
over a range of luminance values.

I agree, but the data is already split into RGB components before it
gets to the monitor. The monitor can't make up the colours inbetween;
it doesn't get given that information, so there's no point the light
generating it.

The display can and does make the colors in between from combinations of the
primaries. It DOES get the information on the mix of those colors but that
information is based on assumptions about how the display will produce the
image. When an engineer designs a camera, they are trying to match the
output of R,G,& B to the Standard Observer curves, not filtering it to
narrow band output at a particular frequency. When the color matrix in the
display recreates that RGB information, it contains the mix that will
produce the intermediate colors. If the display only produces a narrow
spectrum for each primary, the maker of that display has to account for that
in the color decoder and map the colors to what the display can create. It
can create the same colors but the mix to get any particular color may be
very different than a standard matrix calculation would produce if the
spectrum of the display primaries is very narrow compared to the CIE curve
( or CRT monitor response) upon which a camera is calibrated.

The bottom line is, there is more to the story than you are assuming.
Manufacturers get it closer or not, it depends on the execution of their
particular flavor of the technology.

Leonard