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Colour Perception

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Celebaelin
481174.  Fri Jan 16, 2009 9:38 am Reply with quote

I'm not sure how well known this is but I was watching a TV program the other day and he was going over the reason why we percieve objects as being a particular colour and I was struck again by just what an odd concept it is.

Take leaves; what colour are they usually?

Green right? Wrong, the reason why we percieve most leaves as green is that they aren't anything to do with greeness.

Well obviously they ARE because we define what colour something is by the light it reflects but leaves are generally set up (evolved) to absorb light in the higher energy portions of the spectrum and what's left over, the low energy bits, is green and that's why we see leaves as green. But the reflected light from a leaf is the useless bit as far as the function of the leaf in photosynthesis is concerned, it's a totally co-incidental by-product of the actual business of 'being' a leaf, of performing foliate-type functions if you will (or not, of course, if you won't).

Does anyone else think that's wierd 'cos it kinda freaks me out if I think about it too much. Our eyes actually produce a sort of colour negative of the properties of the materials around us. These materials absorb light dependent on the match between incident radiation and the ability of that energy input to excite electrons in the chemical structure of whatever the radiation falls on. The eye exploits the chemical properties which materials do not have to enable us to see those materials. To do it any other way we would have to create some form of radiation (bioluminescence of some sort) then compare what was reflected with what was emited.

It's logical sure but it's just a bit... strange.

 
Davini994
481186.  Fri Jan 16, 2009 9:45 am Reply with quote

Green light enters our eyes... therefore leaves are green.

What's the problem? ;)

This links back to the question of what colour is a mirror?, and normal incident spectrum.

A mirror is still white, even if everybody else who posted disagreed with me;)

 
Celebaelin
481200.  Fri Jan 16, 2009 9:56 am Reply with quote

Thinking about it there are a couple of flaws in what I said. Firstly the colours of some materials are caused by electrons dropping back from an excited state to a lower energy state when the energy released happens to have a wavelength in the visible spectrum so that's a complication. Secondly we could have developed a sight organ which would monitor incident light to compare with reflected light negating the need for a bioluminescent organ; although that would be a pretty cool thing to have and certainly handy in power-cuts etc.

 
Southpaw
481270.  Fri Jan 16, 2009 10:52 am Reply with quote

Even more interesting is how the brain interprets what falls on the retina, how it gives us 3D vision, and how the brain economises by taking shortcuts and making assumptions. It makes you think, if the brain is making a lot of stuff up, what is actually going on.

I recommend Stephen Pinker's How the Mind Works for more info on this. Brillyunt.

 
zomgmouse
481826.  Sat Jan 17, 2009 6:24 am Reply with quote

That is Quite Interesting, that we see things for the one colour they aren't.

 
Posital
481842.  Sat Jan 17, 2009 6:39 am Reply with quote

Our eyesight just doesn't do light justice.

Any perceived colour we see can be created simply mixing three fixed frequency colours - whereas there are in fact a near-infinite number of fixed-frequency colours.

 
Davini994
481867.  Sat Jan 17, 2009 6:55 am Reply with quote

Near infinite? I don't see any reason why the spectrum is discrete, QM or no. Why so?

Creating wavelengths (colours) by mixing other wavelengths (colours) is a very odd concept indeed, and one I can't say I understand properly.

 
Posital
481932.  Sat Jan 17, 2009 8:51 am Reply with quote

Davini994 wrote:
Near infinite? I don't see any reason why the spectrum is discrete, QM or no. Why so?


Well - I'm just aware that there are theories that both space and time are quantised - I think the space one is related to string theory - not sure where the time one comes from.

And if energy is also quantised - then I'm assuming that there might be physical limits to the possible frequencies in EM radiation - there may be other limitations too.

It's all a bit out there and up in the air - but I'd hate to simply say there are an infinite number of frequencies as it makes too many assumptions. And to say near-infinite is definitely more QI.

 
Davini994
481943.  Sat Jan 17, 2009 9:25 am Reply with quote

Quote:
And to say near-infinite is definitely more QI.

Not if it's wrong! I'm not sure whether it is or it isn't now.

I was thinking that it must be infinite, as any GUT must include properties of GM, including that wavelengths can be scaled. But is the metric of space quantised, and therefore that scaling factor?

I have no idea.

 
Posital
482082.  Sat Jan 17, 2009 11:28 am Reply with quote

Davini994 wrote:
Quote:
And to say near-infinite is definitely more QI.

Not if it's wrong!


I have to disagree - we all have to make decisions about how to generalise our descriptions of reality - I just chose a more interesting one.

Quote:
Creating wavelengths (colours) by mixing other wavelengths (colours) is a very odd concept indeed, and one I can't say I understand properly.


Misunderstanding here - I was talking about creating perceived colours (not wavelengths) - which is basically how the screen you're looking at works.

 
Davini994
482130.  Sat Jan 17, 2009 11:40 am Reply with quote

Posital wrote:
I have to disagree - we all have to make decisions about how to generalise our descriptions of reality - I just chose a more interesting one.

You are welcome to make generalisations that are wrong and find them interesting; as you say, I take a different view.

Quote:
Misunderstanding here - I was talking about creating perceived colours (not wavelengths) - which is basically how the screen you're looking at works.

Why does my screen look red if it is not so then?

 
Posital
482159.  Sat Jan 17, 2009 11:49 am Reply with quote

Davini994 wrote:
Why does my screen look red if it is not so then?


It's red because the light coming from the screen fires your red receptors (or whatever) more than any other and give you the perception of redness.

But this perception of red can be triggered in so many different ways using different mixtures of different visibly wavelengthed light.

NB: I am assuming that your experience of red and the wiring of your anatomy is the same as I understand it from books, education, TV, conversations, etc with other people whom I believe are sentient beings who operate like me. I have not experimented on your eye to check that it - and the space-time in which you inhabit operate in a similar way to how I believe mine does - or even that the words I am using here even have the same meaning to you as I expect them to have.

Maybe I didn't need to say this?

 
Davini994
482190.  Sat Jan 17, 2009 12:03 pm Reply with quote

Ah, that's very interesting. I was always thinking that... well I don't know what I was thinking. That somehow there was vector addition going on. I hadn't thought about it too much, clearly.

So the human eye can't distinguish between some pure wavelengths and combinations of wavelengths. And then Aliens might view VDUs completely differently to us. Awesome fact.

Posital wrote:
Maybe I didn't need to say this?

:)

 
Davini994
482217.  Sat Jan 17, 2009 12:34 pm Reply with quote

Wiki wrote:
Color constancy is an example of subjective constancy and a feature of the human color perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions.

Colour constancy, how interesting is that? Our brains are giving us an adjusted answer and can't specifically tell us what the source data was.

http://en.wikipedia.org/wiki/Color_constancy

 
Ion Zone
489843.  Mon Jan 26, 2009 5:43 pm Reply with quote

Quote:
A mirror is still white



Silver is classed as a white metal, gold yellow :P

 

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