Re: Flesh tones

SpamTrapSeeSig wrote:
In article <h9m258$4ft$1@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Ivan
<ivan'H'older@xxxxxxxxx> writes
Tony Quinn wrote:
Most forms of modern lighting are not broad spectrum, so *YES* it is
exactly as you describe it.

Thanks Tony, is it not possible to incorporate any kind of electronic
colour fix for the race coverage, and wouldn't the lighting used by
the camera crews to illuminate the BBC interviewers automatically be
balanced for natural colour, in the same way as presumably it would
be at any other venue?

Tony gave you a complete, if terse, answer above.

All colourimetry (to a greater or lesser extent) presumes black-body
radiation and smooth curves for light emitters and sensors. If you
don't have these, you cannot achieve 'natural-looking' colour (as a
working definition: the result of reflected daylight from
'normally-coloured' objects into a normal naked eye, allowing for the
eye's own varying sensitivity across the spectrum).

Spectral lines from discharge lamp technology cause varied effects,
but generally speaking, the more 'efficient' the lamp, the less
spectral lines there are, with more energy concentrated in each. This
_cannot_ be compensated for. The best (worst) example is low-pressure
sodium lamps, used for decades as street lighting - the orange glow,
IIRC comes from just two wavelengths emitted (the 'Sodium D-lines')
of the spectrum. No colour is possible because there is no light
available in other parts of the visible spectrum.

Some discharge technologies, notably Xenon (flash guns) and HMI
(high-pressure Mercury), produce sufficient spectral lines,
sufficiently close together, to achieve very good colourimetry. It's
notable though that even they have to be controlled carefully to
prevent unwanted artefacts. In the case of Xenon, there is usually a
yellow coating on the tube (or a filter in front of it), to block the
high proportion of UV emissions. This would otherwise throw off most
colour sensors, chemical or electronic, and in large tubes or close
proximity would actually be dangerous (similar to a welding arc).

I don't know about HMI lamps, but I'd be surprised if there aren't
similar design issues.

To come back to Singapore: they're already using huge amounts of power
with the discharge lamps they have. It's a compromise between cost and
image quality. I guess they couldn't afford cables and generators for
a broad-spectrum approach.



Thanks for the detailed explanation Simon, I can see the difficulties of trying to compensate for something that's not there in the first place.

It was just that I've seen some quite ordinary digital cameras do such a good job with their automatic colour balance under artificial lighting conditions, that I assumed the ultra expensive kind of high end kit used by the professional broadcasters might somehow be able to do a much better job.

However that being said the picture quality of the actual race was excellent as usual, despite it not being in HD.. hopefully next year!

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