Starspun

Could someone please explain (when time permits) how color is perceived? I think I saw a thread awhile back where someone was saying that matter was not colored; our brain perceives color.

Is all matter grey? Is grass a grey color instead of the green that I perceive it to be? What is lights role in color perception?
I have tried to reason through these questions, but I don't think I understand the picture, in a manner of speaking. Any insight would be appreciated.

simian

Quick answer: we perceive photons coming from objects. Certain wavelengths are certain colors (we don't perceive most wavelengths - they are too long or too short for us to see). The light bouncing off an object is the portion of the spectrum that object does not absorb. Example: plants generally do not use green for photosynthesis - it is not absorbed - it is what bounces off the plants and you see. I will leave it to the physicists to describe what color things "really" are. As "The Science of Diskworld" would have it, this probably qualifies as an "answer for children" - close enough to correct to be useful, but probably not absolutely correct.

Simian

Undercurrent

Light frequency, distribution of frequency exist in the real world, and are detectable by instruments (other than humans). Colour (even grey) is the interpretation of frequency distributions by the brain, and thus doesn't "exist" outside the brain. It's a property of the instrument, not the thing being measured.

E.g. I can describe "700nm" to you even if you'd never seen light of wavelength 700nm. These kind of descriptions make sense even for blind people, or for wavelengths of light that we can't see. If you'd never seen "blue" however, I couldn't describe it to you. The only reason we can talk about "blue" is because we have both experienced objects that people have called blue. Without that context, there is no blue.

m.

m.

Starspun

I was looking at the light waves from thewrong perspective. Thanks for clearing up my confusion.

John Page

<a href="http://faculty.washington.edu/chudler/eyecol.html" target="_blank">color vision link</a>

Try this link, interesting stuff like we can;t perceive both blue and yellow at one location. Visual perception of colors is a lot more than light hitting the light sensitive cells in the eye.

I can't remember the name for it but people watching black and white TV could sometimes say they tell what color someones hair or clothes were. Some of them were correct and apparently our brains do contrast/greyscale comparisons to do some color deduction.

Cheers, John

Starspun

Thanks for the link, John Page.
The question begs, what does a non-illuminated object look like? Would there be anyway to visually detect something without the light spectrum, which contains the colors? Humans probably couldnt due to not being able to see 'in-the-dark', but, are there other methods? How would one describe, visually, a leaf without a light spectrum? OR, is it impossible to detect visually at which point we would need to rely soley on another of our senses?
Man, I hope that question makes sense.

tronvillain

Starspun:
A non-illuminated object doesn't "look like" anything, at least if we assume a normal human visual system. Oh, one can attempt to assemble a "mental image" (which are not pictures in your head) from information obtained by channels other than vision but they are usually quite crude.

Still, there are probably other systems that could be used to "see" - all that is required is appropriate sensory apparatus and the correct processing. Touch could be used to approximate vision, but it is slow and we just don't have the processing to do the required transformations. What else could be used? Of the human senses, hearing might serve, providing sonar with the correct processing. Beyond that, who knows? Perhaps electrical/magnetic fields.

John Page

Hmmm. Night vision goggles that shift the wavelengths into the visible spectrum? Well, the color is not actually in the light and we don't see in "absolute" color anyway. The brain appears to be able to take reference readings and auto adjust for light settings etc.

Small anecdote. I lived on Malta, a small fairly arid Mediterranean island with few trees and not many bushes. Low rainfall. Stayed there for six months then flew to the UK and descending thru the clouds though "Wow, the grass is really green". Only then did I understand why many Maltese who had visited the UK had told me "I like to UK, its very green".

Finally, there is a condition known as synasthesia where the processing from the senses gets mixed up so people kind of see voices, hear colors etc. I'm not sure this answers your question but I thought it worth throwing in.

Cheers, John

Starspun

That, would be the freakiest thing one could exp imho.
And yes, the question is answered. Thanks for replying.