Leonard Caillouet wrote:
wrote in message
...
Arfa Daily wrote:
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William Sommerwerck wrote:
I guess it comes down to definitions and how 'full spectrum' is
perceived.
Rightly or wrongly, I tend to think of it as a spectrum which
contains
the
same component colours in the same ratios, as natural daylight...

That's a reasonable definition for a video display, but it's not
sufficient
for source lighting. It's difficult to make a "full spectrum"
fluorescent
lamp, especially one that produces good color rendition for
photograpy.


but I guess even that varies depending on filtering effects of cloud
cover and haze and so on. Even so, I'm sure that there must be some
definition of 'average spectrum daylight', and I would expect that
any
display technology would aim to reproduce any colour in as closely
exact a way as it would appear if viewed directly under daylight.

The standard is D6500, a 6500K continuous spectrum from a black-body
source.
What you suggest is, indeed, the intent.


TBH I think this is overplaying the significant of daylight. Almost
any monitor is adjustable to suit preferences of anything from 5000K
to 10,000K, and some go lower. None manke any attempt to copy the
colour spectrum of daylight, they merely include the same colour temp
as daylight as one of the options. None of the major display types
have any ability to copy a daylight spectrum, as they're only RGB
displays.


NT

But take account of the fact that we're talking domestic television sets
here, not computer monitors. For the most part, TV sets do not display
the
same type of content as a computer monitor, and do not include user
accessible colour temperature presets or adjustments,

fwiw my main set does, and I'm sure its not unique. Generally though a
TV is a much lower quality animal than a monitor, and displays much
lower quality data.


which is why I made
the point earlier that in general, LCD TVs are set correctly 'out of the
box'.

because they can be. CRTs are more variable, and the circuits used to
drive them a lot less precise, partly because CRT sets are generally
older, and the sort of standards expected in monitors have only begun
crossing over to tvs in recent years.


As far as overplaying the significance of daylight goes, I'm not sure
that I
follow what you mean by that. If I look at my garden, and anything or
anybody in it, the illumination source will be daylight, and the colours
perceived will be directly influenced by that. If I then reproduce that
image on any kind of artificial display, and use a different reference
for
the white, then no other colour will be correct either,

what makes you think that just one specific colour temp is 'correct'?
Real daylight is all over the place colour temp wise, and the end user
experiences those changes without any problem. Also any self
respecting monitor offers a range of colour temps, since its nothing
but a taste matter


which was ever the
case when CRTs were set up to give whites which were either too warm or
too
cold, even by a fraction.

but thats down to historic reasons, customers never expected precise
colour temp, and screens were routinely set up by eye. The circuits
involved couldnt set themselves up the way a modern LCD set can, there
was normally no feedback on colour channels, just open loop CRT gun
drive on top of a massive dc offset, so the systems were inherently
variable. Plus the fact that CRT gamma was often way off from the real
world made it hard, or should I say impossible, to set such sets to
give a faithful reproduction in other respects anyway.


Maybe we're talking at cross purposes here, or I'm
not understanding something properly, but it seems to me that the colour
temperature and CRI of the backlighting on an LCD TV, would be crucially
important to correct reproduction of colours.

It has almost nothing to do with it, because the level of each colour
channel output on the screen depends on both the light source and the
settings of the LCD R,G,B channels. Within reason, any temperature
colour backlight can produce any temperature colour picture.


All I know is, is that the flesh tones were poor on the example that I
saw,
compared to other LCD TVs which were showing the same picture. The
fundamental difference between those sets and the Sammy, was the CCFL vs
LED
backlighting, so it seems reasonable to draw from that, the inference
that
the backlighting scheme may well be the cause, no ?

Arfa

Its just a guess. In fact any desired flesh tone can be reproduced
using almost any colour temp backlight, certainly anything from 3,000K
to 10,000K. Think about the process, you've got 3 colour channels,
each of which has a given level of light from the backlight, which is
then attenuated to any desired degree by the LCD pixel.


NT


While this is true, it would be virtually impossible to get all colors right
with some arbitrary color backlight. You could get a subset right and get
all the others completely wrong.

Leonard

With each colour channel you've got everything available from
backlight output x LCD max down to backlight output x LCD minimum.
AFAIK that covers every flesh tone on this planet, unless one goes
down to 2000K backlight or some other very extreme value.


NT