[opendtv] Re: New Chips Improve Color TV Dramatically
- From: jeroen.stessen@xxxxxxxxxxx
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 24 Jun 2004 14:21:13 +0200
Hi,
Mike Enright <menright1@xxxxxxx> wrote:
> I would also like to ask about that 55% of gamut figure
> (for CRTs) in the linked article.
The "100% gamut" includes all spectral colours, which are only
physically realizable with lasers. Any N-primary display can
render only the colours inside an N-cornered polygon. With N=3
this is a triangle, which has obviously a much smaller gamut area
than the 100% gamut inside the spectral locus. If then also these
N primaries are not spectral colours themselves, then the gamut
area shrinks even further, e.g. to a smaller triangle.
But is that a problem ? If we look at the gamut of colours
occurring in nature, and I do not have a good reference handy
but look for example at http://www.colourware.co.uk/steve/sensor.pdf
page 5 (numbered 54), then this gamut area is not so large either.
Draw a reasonably large RGB triangle around it, and you're done.
This doesn't mean, of course, that we would not _want_ to make
a larger gamut. If properly challenged we would create an ink or
paint to render it. Or design an extended-gamut (MPC) display.
> To what extent is that issue caused by off-color
> phosphors in CRTs and short-cuts in NTSC decoding?
Not, I think. The limits are probably simply in having chosen
the primary (phosphor) colours as what they are: approx. sRGB.
This is obviously a legacy from phosphor based CRTs. It is not
possible to choose a phosphor at will, because it may be too
inefficient (deep blue), too slow (original NTSC green) or too
toxic (red that contains Cadmium). These considerations have
given us the RGB primaries that we are using now (sRGB, Adobe RGB),
and the most used sets (which are all close to sRGB) seem to cover
"only 55%" of the total possible viewable colour gamut area.
This covers almost all colours occuring in nature and culture.
And yes, for some purposes we will want to have more than that.
Referring to a percentage can be deceptive, because it has to
be stated in which space (x,y) or (u,v) it is defined. Not all
gamut increases are equally important to the human eye. Mapping
the colours onto the proper space corrects this, e.g. it gives
less importance to an improved green. Good red is more important.
So any reference to an area percentage must be taken with a grain
of salt, as some improvements are more important than others.
I wonder what the world would look like to an individual
(animal ? extraterrestrial ?) whose eyes have more than 3
channels. What does an N-dimensional colour space look like
if N > 3 ? How would you choose a colour for your car ? ;-)
Regards,
-- Jeroen.
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| From: Jeroen H. Stessen | E-mail: Jeroen.Stessen@xxxxxxxxxxx |
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