Re: Flesh tones

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.

Regards,

S.
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