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### Re: How many colors does a rainbow have?

by BrowserUk (Pope)
 on Jan 25, 2009 at 16:02 UTC ( #738779=note: print w/replies, xml ) Need Help??

in reply to How many colors does a rainbow have?

3. The rest are synthesised (or not) by the brain of the observer.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
• Comment on Re: How many colors does a rainbow have?

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Re^2: How many colors does a rainbow have?
by moritz (Cardinal) on Jan 25, 2009 at 20:05 UTC
By that token maybe 4, because we also have separate receptors for brightness?

Oh, and I've heard there are people with some mutations who have pigments for two different shades of red, so they can actually see RRGB+brightness.

By that token maybe 4, because we also have separate receptors for brightness?

I don't think that you can classify intensity as a fourth "color".

If you increased the intensity of the spectural components in the rainbow whilst leaving their ratios unchanged, the observer would tend to squint, closing the iris, to reduce the overall amount light (number of photons), reaching the retina, with the result that the observer would perceive the same information.

Besides which, the rods only tend to come into play in low-intensity situations, when color information becomes distorted anyway. For example, at night, the green leaves of a rose tend to appear brighter than the red of the petals.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
Re^2: How many colors does a rainbow have?
by Gavin (Chancellor) on Jan 25, 2009 at 18:34 UTC

"3" As in the others can be "synthesised" as a mixture of Red Green and Blue?

But what if you are color blind? Do you fill in the gaps or does it just become gray?

I thought it was Red, Blue, and Yellow.

Update: I obviously do not know what I am talking about :(

And you didn't even know bears could type.

I thought it was Red, Blue, and Yellow.

That's what they teach in elementary school, but they're talking about paint, not light, when they teach you that. And it's still not quite exactly right. Technically it would be closer to magenta, cyan, and yellow, but they don't want to teach you words like "magenta" and "cyan" in kindergarten.

Each of these three basic pigments absorbs one of the major colors of light that the eye sees. (Of course, the cheap paints you work with in gradeschool don't do so perfectly, by any means, but this is how it's supposed to work. If your pigments were perfect, mixing them all together would give you black; in practice, you usually get a murky brownish color, because the pigments you have are imperfect.)

For instance, yellow pigment absorbs blue light, so what gets reflected is mostly green and red light; when the eye sees green and red, the brain interprets it as yellow. The other two pigments work similarly. For further reading on this subject, see CMYK color model.

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3 - Red Blue and Yellow, the other colors are achieved via dithering.
Re^2: How many colors does a rainbow have?
by mr_mischief (Monsignor) on Jan 26, 2009 at 16:17 UTC
Technically, isn't it that the colors are there (as actual separate yet overlapping ranges of wavelengths that partly trigger two or more sets of cones) but we make do with only three (usually) sets of cones to detect them since they trigger inexactly?

I'll ramble a bit, since the color spectrum is one of my favorite topics for thought experiments. I've used readmore tags so it's easy to choose not to look at what many of you might find boring.

Afaik, we know that healthy people have the same chemistry of colour-sensitive cells. I do not know nothing relevant about further signal-processing, I only know that the graphics or other professionals have common, healthy sight. They are just trained to distinguish more colours than we can name :>)

But, do not forget octarine

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