OT: Moon and Jupiter (2023 Update)

[whisky-dave]

The andorians in star tek call us 'white people' pink skins

[charles]

from my colourimitry notes: Brown is dirty Yellow

[Max Demian]

There are lots of colours that aren't on the spectrum. [1] Pink for example. It's a matter of saturation.

[1] Is the rainbow autistic?

[whisky-dave]

[whisky-dave]

Dirty is not really a decriptive property of colour. Such as having a dirty mind doesn't imply you don't wash etc..

[Vir Campestris]

Errmmmm... Orange is a colour that doesn't exist. It's just a blend of red and green. Put something orange on your computer screen, and use a magnifying glass.

Human eyes are _really_ bad at colour. Red, Green, Blue and that's it.

Andy

[Andy Burns]

Then get your prism out and look between red and yellow?

[Martin Brown]

Orange is the colour of a particular wavelength of light on the spectrum just as much as the old monochromatic yellow 590nm sodium street light.

If you look at a spectrum of white light then you see the colour that our brain perceives for each wavelength. It is a pure colour and cannot be broken down any further.

The computer screen fakes the same stimulus profile using just R, G & B.

Human eyes are not that great at colour compared to some insects but you have it wrong.

The cones on the retina are sensitive to *yellow*, green and blue.

"Red" is computed in the next tier of processing as "yellow - green" and you can play tricks on the brain with a minus yellow bandpass filter.

Red is important in the wild because many ripe fruit are red so seeing them from a distance is advantageous to survival.

However, it is possible to fake almost every colour that we can see using a combination of R, G and B pixels. Normal colour vision has a remarkably large number of colours it can discriminate.

People with defective or enhanced colour vision see things differently.

[The Natural Philosopher]

No, the problem is that colour itself is very variable and subjective

[The Natural Philosopher]

Exactly, There are an infinite number of spectral densities in the visible range

Orange is a colour that can be completely monchromatic - one wavelength alone will look 'orange'.

but you need all wavelengths for pure 'white' and you won't do 'pink' out of a single wavelength.

[Max Demian]

Actually they've measured the frequency responses of human cones and found that there is one lot sensitive to blue and two in the yellow, quite close together. [1] The brain sorts it out.

The idea that they are red, green and blue came from Famous Scientist Maxwell [2] I think. Photography and video can probably use any three colours that are reasonably separated, so colours can be chosen that have convenient pigments/dyes and phosphors.

[1] This makes sense in relation to the vision of non-primate mammals, who just have blue and yellow cones. The gene for yellow could be duplicated and one copy mutated so it has a slightly different frequency response (in primates). [2] He who demonstrated colour photography by Cheating. He projected the image of a scarf onto a screen which included red - but photographic emulsions in those days weren't sensitive to red at all - you could develop negative plates (and film) in a red lit darkroom. The red filter he used to take the picture must have passed some other colour as well.

[Martin Brown]

He was just demonstrating it in a very convincing manner. It was possibly known as far back as Newton who first split white light with a prism and then recombined it. Maxwell's demos were very good indeed.

He didn't actually cheat - he just got lucky with choice of red filter!

Lumiere's Autochrome process in 1907 was the first usable true colour process (even then the emulsions have a safe light blind spot at 500nm).

A few of their images survive sufficiently unfaded to be restored.

Some of the red-green colour blind have non-primate like vision.

I recall a much feared senior cosmologist who once asked a question of a nervous graduate student giving a seminar. He was visibly trembling as the Professor spoke - his question "which one of those is the red line?"

[Joe]

"And for those of you watching in black and while..."

[Joe]

To an extent. To produce the maximum range of colours, primary (additive) sources must be as close as possible to the extremities of the 'colour horseshoe' (CIE 1931 diagram), which makes them a red, a green and a blue. For three arbitrary primaries, the colours which can be displayed are those inside the triangle formed by placing the primaries on the horseshoe.

[The Other John]

Spot the crap journalism: 'the starch grains were thousands of millimeters wide' :)

[Max Demian]

That doesn't show that three *other* colours would not give a similar effect.

(Splitting the spectrum and recombining it is irrelevant; we're talking about how it's possible to give the impression of all the colours of the spectrum (and more) with just three colours.)

But the red on the screen wasn't actually red.

That's more or less what I said.

Paywall.

When I was at school one of the other boys complained that he could only see three colours when we did the spectrum in "General Science". I don't remember what the teacher said; I expect he was told to shut up. He could have discussed the genetics of colour blindness and why it is mainly boys who have it. Or speculated on why it persists in the population. (Some animal camouflage doesn't work for colour-blind people.)

[Tim Streater]

IIRC Mr Cheating's film was sensitive to IR, which was reflected by the scarf.

[The Natural Philosopher]

Basically that is on account of the colour response of the eyes cones Colour vision, like sex organs, shows no evidence of intelligent design

[Martin Brown]

UV - higher energy photons affect classic silver emulsions more.

CCD's tend to have extra IR sensitivity.

It required additives to make IR sensitive silver emulsions and red sensitive ones too for that matter. There was still a blind spot in most of the "true colour" films around the green 500nm OIII line which could be used as a safelight when processing colour.

It had the side effect that the first ever proper full colour images of the brightest nebulae were not made until the early 1970's. Prior to that they were all rose pink and turquoise on early Palomar colour slides despite some of the brightest ones looking visually apple green.

Also to get flesh tones more nearly right for popular colour films they "lost" the errors along the line of purples and there were a few purple flowers that were impossible to photograph accurately as a result.

[Max Demian]

Well it had to evolve incrementally. As I suggested, the "yellow" genes must have duplicated, then one copy mutated. That's why they are close together.

An intelligent designer would have chosen three well separated colours.

And made a better job of the knee. It's a simple hinge after all.

And not gone to the trouble of making hands/arms that can thread a needle /and/ hurl a rock. We would have had two sets of upper limbs: the upper pair for delicate work and the lower for heavy lifting.

But we need our lower limbs for locomotion: we only have four limbs. We're tetrapods, not hexapods; we're not insects.