What is the Definition of Color According to the CIE?

[FactChecker]

In physics, green is light in the wavelength range 520 to 570 nm. But the human eye does not have sensors for each frequency. It senses high, medium, and low frequencies to give us all the perceived colors. It is a common misconception that light of any color can be made by combining 3 colors like red, green, and blue, but that is just how we fool the eye. In physics, you cannot combine colors to obtain another color.

 

[sophiecentaur]

In physics, green is light in the wavelength range 520 to 570 nm. But the human eye does not have sensors for each frequency. It senses high, medium, and low frequencies to give us all the perceived colors. It is a common misconception that light of any color can be made by combining 3 colors like red, green, and blue, but that is just how we fool the eye. In physics, you cannot combine colors to obtain another color.

'Colour' is not Physics. Green is not a wavelength. You can definitely not produce spectral green on a TV screen. You have to get these things in perspective and not over simplify. (I am not disagreeing with your post - I am expanding on it.)

 

[bobie]

'Colour' is not Physics. Green is not a wavelength.

That is true, but also "note" ,"music" is not Physics. I don't see why we cannot apply the same standard.
"A 7" has lots of frequencies around 3520, and it is recognized as such, independently of the tuning of the instruments. The difference with visible light is that we distinguish 12 "notes" and only 6 "colours".
Stretching our fantasy, we might talk of orange as "red sharp" or "yellow flat", or say that violet resembles red because it is an "octave above" red
Why not?

 

[sophiecentaur]

Music and colour are human experiences. We can associate them with physical quantities but there is a limit to how relevant it is. Obviously, we use technology to provide our senses with stimulae but there isn't a causal path from perception to stimulus ( it only works in the other direction).
I put my thoughts into threads like this in an attempt to get people to stop making invalid inferences about the relationship between physics and the psychology of senses.

 

[Pythagorean]

Music is a particularly interesting case. The math doesn't add up if you approach a note two different ways unless you distribute the error between all the notes (a technique called equal temperament tuning). If you try to force music theory on the physics (by "just" tuning), you'll end up with that error, called a syntonic comma.

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

 

[voko]

That is true, but also "note" ,"music" is not Physics. I don't see why we cannot apply the same standard.
"A 7" has lots of frequencies around 3520, and it is recognized as such, independently of the tuning of the instruments. The difference with visible light is that we distinguish 12 "notes" and only 6 "colours".
Stretching our fantasy, we might talk of orange as "red sharp" or "yellow flat", or say that violet resembles red because it is an "octave above" red
Why not?

Because "colour" is similar to "timbre" in music, not to "pitch". There are some schemes where colours are coded by three parameters, one of them being the "hue", which suggest that we could treat the hue similarly to the pitch, but the problem is that those schemes are artificial. That's not how our brains perceive colours. Our brains can figure our the higher pitch of two sounds, but they simply do not have a natural notion of the "higher hue" (unless we are speaking of the brains that have been trained by years and years of professional practice).

 

[sophiecentaur]

Because "colour" is similar to "timbre" in music, not to "pitch". There are some schemes where colours are coded by three parameters, one of them being the "hue", which suggest that we could treat the hue similarly to the pitch, but the problem is that those schemes are artificial. That's not how our brains perceive colours. Our brains can figure our the higher pitch of two sounds, but they simply do not have a natural notion of the "higher hue" (unless we are speaking of the brains that have been trained by years and years of professional practice).

I don't think there's much joy to be had in the Compare and Contrast approach between the senses. You don't come across pure, single frequency sounds or light in real life. Colours that we see are never (very very seldom) single frequencies of light and sounds we hear are seldom single tones. Comparing hearing and colour vision on the basis of single frequencies is pretty fruitless but you can say that your ears are less easy to 'fool' than your eyes in that respect, because the cochlea is a pretty good spectrum analyser and the retina is a lousy one.
The idea of relating colour to timbre is interesting and I see where you're coming from.
"Higher" is not a useful concept in a multi-valued quantity as with tristimulus colour vision - unless, perhaps, in reference to near- spectral colours.
I must say that some of the ideas on this thread are a lot more objectively useful than what you can read elsewhere when colour is dealt with by 'creative' users of colour. There is such a lot of fanciful twaddle to be found in that direction - plus, to be fair, a decent amount of pragmatic advice for the practitioner of colour graphics.

 

[bobie]

suppose the light is formed by a bunch of intermingled yellow and blue LEDs, packed so close together that you can't see the individual LEDs.) You'll never see green. You'll see a muted yellow, or a muted blue, .

What happens if we mingle blue and red LEDs, do we get yellow?

 

[voko]

Take any application, such as the Paint in Windows, and go to its colour mixer. One of the modes is RGB (Red-Green-Blue). Maxing out R & B, and G = 0, you get some pinkish-purplish colour.

 

[sophiecentaur]

What happens if we mingle blue and red LEDs, do we get yellow?

The questions you keep asking lead me to suspect you are not reading around this subject at all - just relying on Q&A on this thread. Have you not read about the CIE colour chart and the way you can synthesise colours ac cording to their position on that chart? All this information is in the links you have been given.
Just how much spoon feeding do you want?

 

[FactChecker]

'Colour' is not Physics. Green is not a wavelength. You can definitely not produce spectral green on a TV screen. You have to get these things in perspective and not over simplify. (I am not disagreeing with your post - I am expanding on it.)

"color" is most certainly defined in physics. It is central in the study of prisms, black body radiation, color energy, quantum mechanics of light, physical chemistry. Newton, Einstein, and many others have made put it on a very solid foundation in physics.

 

[sophiecentaur]

"color" is most certainly defined in physics. It is central in the study of prisms, black body radiation, color energy, quantum mechanics of light, physical chemistry. Newton, Einstein, and many others have made put it on a very solid foundation in physics.

You are confusing colour and wavelength in all these examples.
I'd like to see a quotation by Einstein relating colour to Physics - except to describe the colour of a certain wavelength of monochromatic light.
Newton is far too long ago to quote as a definitive authority about many things. If you remember, he was a believer in Alchemy !

 

[AlephZero]

Newton is far too long ago to quote as a definitive authority about many things. If you remember, he was a believer in Alchemy !

The reason Newton decided there were 7 colors in the rainbow, was either to match the number of known objects in the solar system (but you need a bit of creativity to make that logic work, considering Galileo had invented the telescope and discovered some of Jupiter's moons, and Newton himself had studied the orbits of comets), or else it was to match the notes in the musical scale with different colors.

Both of the above were believed by Aristotle, and that was good enough "proof" for Newton that 7 was the correct number, so he added Orange and Indigo to the 5 colors he could actually see with his prism experiments.

Isn't science wonderful, with the benefit of hindsight

 

[Pythagorean]

Unfortunately, you are not in charge of the English language. Color has been used by scientists in connection to frequencies of light since long before you were born.

The OP defined color as the subject experience. Yes scientists sometimes use color and wavelength interchangeably, but since the OP was nice enough to define things for us, your posts just seem like pedantic semantics.

 

[FactChecker]

The OP defined color as the subject experience. Yes scientists sometimes use color and wavelength interchangeably, but since the OP was nice enough to define things for us, your posts just seem like pedantic semantics.

The OP: The OP is a very good question. It asked about several alternatives, from subjective, to a mixture of frequencies, to defined by one frequency. The truth is that it is used differently in different pursuits. I believe this is the source of confusion that lead to the OP.

In art, photography, TV, printers, etc.: For fooling the human eye, colors are usually obtained by mixing three colors of low, medium, and high (visible)frequencies. This is because the human eye identifies a single color by it's combined effect on sensors for low, medium, and high frequencies. The eye can be easily fooled that way. Mixing more than three colors can do a better job of making the human eye perceive purer saturated colors.

In physics: There is no way to really combine multiple frequencies to get a single frequency. So in the world of physics, where a color is identified with a single frequency, three colors cannot be combined to get a single color. A prism or spectrograph easily separates them, whereas the true single-frequency color does not separate.

 

[OmCheeto]

Unfortunately, you are not in charge of the English language. Color has been used by scientists in connection to frequencies of light since long before you were born.

Ah! Hahahahaha!

hmmm...

Should we perhaps put a philosophy major from China in charge of the English language?

I'm neither from England, nor am I a scientist, so I would answer the OP's questions thusly:

I read many articles but still I do not know what are colours like green:
Is it
-a subjective quality that is made up in human brain, or

yes

-the result of sum of yellow and blue, or

yes

-the presence of radiations of two frequencies in the same source, or just

what?

-the quality of a radiation of a single frequency, as wiki says, in the range between 570 and 590 nm?

Corrected by D H; "Green (spectral green) is light between 520 and 570 nm", or 560-490 nm, per wiki(whatever...). But this is how I would describe "Green" to an alien in one of the newly found exoplanets.

Thanks for your help

You are quite welcome.

 

[sophiecentaur]

The OP: The OP is a very good question. It asked about several alternatives, from subjective, to a mixture of frequencies, to defined by one frequency. The truth is that it is used differently in different pursuits. I believe this is the source of confusion that lead to the OP.

In art, photography, TV, printers, etc.: For fooling the human eye, colors are usually obtained by mixing three colors of low, medium, and high (visible)frequencies. This is because the human eye identifies a single color by it's combined effect on sensors for low, medium, and high frequencies. The eye can be easily fooled that way. Mixing more than three colors can do a better job of making the human eye perceive purer saturated colors.

In physics: There is no way to really combine multiple frequencies to get a single frequency. So in the world of physics, where a color is identified with a single frequency, three colors cannot be combined to get a single color. A prism or spectrograph easily separates them, whereas the true single-frequency color does not separate.

You nave to be careful here. The way printers 'mix' colours is entirely different from how the other media, that are in your list, work. In the conventional arts (those which rely on 'passive' colour (paint, pigment, dyes, filters) the colour mixing is subtractive and a whole different set of rules apply. This is where the OP's misconception (or at least, misplaced reasoning) about Blue and yellow 'making' green. Nothing that is produced this way can produce a single wavelength of light (spectral colour).

This statement implies that there is, somehow, a true colour and phoney versions of that colour. All that needs to be said is that a metameric match can be obtained in many different ways. The 'obsession' with spectral colours and the idea that they are representative of the colours we see around us is misplaced. They are not encountered in normal life and our brains are really not familiar with them. Wavelengths 'have colour' but colours do not 'have wavelength'. There is a massive logical distinction. Brown, magenta, pink, orange do not have a wavelength- along with most of the reds oranges, yellows, greens, blues, indigoes and violets we see. It is interesting to note that violet (one of Newton's spectral colours), as defined on the CIE chart, does not even lie on the spectral colour curve.

 

[bobie]

The questions you keep asking lead me to suspect you are not reading around this subject at all -
Just how much spoon feeding do you want?

It seems you are oversimplifying my questions. OP had a wide scope ,now that is getting narrower and narrower: now I am enquiring after physical aspects:
If we project a red beam and a green one onto a white screen we get yellow light: we are overlapping frequencies.
My last question was more subtle than you thought:
- do we get the same result if we put those frequencies side by side?, intermingling and not overlapping sources of light? that would suggest a manipulation by the mind.
When we project two beams (red/green), the radiation from the screen toward the eye has a definite frequency or not?, if we detect it not by the eye but by an instrument is that 580 nm ?
If the answers are yes, then human mind does not make up colours.

 

[sophiecentaur]

It seems you are oversimplifying my questions. OP had a wide scope ,now that is getting narrower and narrower: now I am enquiring after physical aspects:
If we project a red beam and a green one onto a white screen we get yellow light: we are overlapping frequencies.
My last question was more subtle than you thought:
- do we get the same result if we put those frequencies side by side?, intermingling and not overlapping sources of light? that would suggest a manipulation by the mind.
When we project two beams (red/green), the radiation from the screen toward the eye has a definite frequency or not?, if we detect it not by the eye but by an instrument is that 580 nm ?
If the answers are yes, then human mind does not make up colours.

If the sizes of the individual sources are great enough for the eye to resolve, spatially, then we will see two sets of different coloured sources. Once the size and spacing becomes lsee then out resolving power, adjacent colour sensors will see more or less the same light and so we will see the mixture and experience the resulting colour. TV displays are designed to have the phosphor spacing small enough to get good mixing at all normal viewing distances. "Mingling" has the same effect as "mixing".

What possible linear mechanism could make the result of two bands of light (the spectra of the two coloured beams) produce a monochromatic output at some wavelength between the two?
I have to ask whether you are using any other sources of information than the answers you are getting to your questions on this thread? The question is not subtle; it is just very wide of the mark. All this stuff is discussed all over the web and you could easily find out about it. Just follow the links in this thread.

 

[bobie]

This is where the OP's misconception (or at least, misplaced reasoning)..
The 'obsession' with spectral colours and the idea that they are representative of the colours we see around us is misplaced. They are not encountered in normal life.

If my questions are wide of the mark, I do regret it, please ignore them. But I am saying something different.
I have no obsessions. I have a toy laser that emits red "colour": I suppose it does have only one "spectral" frequency, and that "colour or hue" is familiar to me. Besides, in normal life we not only see leaves that probably reflect different hues but also artificially painted objects that probably have less or even one frequency.
Can we fool our brain making up "red" mixing two colours?
Colour, as I said, is just a group of frequencies, that we arbitrarily (yes) group, because they look similar, the same as we consider A7 a frequency of 3519,-20 or 21 Hz while we call 3522.44 G7 sharp.
But our intervention is mostly limited to defining the boundaries, deciding when red becomes "yellow"
You say "colours do not have wavelengths" and it seems a sweeping generalization, some hues do not, but many do have a "range" of wavelengths.
The fact that mind can create some hues doesn not affetct the principle.
"yellow" is a range of frequencies (570/90 nm), and, if I got it right, it is also an illusion of that frequency created in our mind by two frequencies outside that range.

 

[jbriggs444]

You say "colours do not have wavelengths" and it seems a sweeping generalization, some hues do not, but many do have a "range" of wavelengths.
The fact that mind can create some hues doesn not affetct the principle.
"yellow" is a range of frequencies (570/90 nm), and, if I got it right, it is also an illusion of that frequency created in our mind by two frequencies outside that range.

Not just two frequencies. It would be closer to the mark to say that it is the sensation produced some [possibly large] set of spectral distributions. By "spectral distribution", I mean a graph that would be produced if you plotted intensity versus frequency. If you Google the term you can find some pretty ones.

According to some posts up-thread, even this is an over-simplification.

 

[Pythagorean]

When we project two beams (red/green), the radiation from the screen toward the eye has a definite frequency or not?, if we detect it not by the eye but by an instrument is that 580 nm ?

First of all, the beams each have more than one frequency. They certainly have a distribution of frequencies. And it's not like nature divides frequencies into integer nm like we tend to anyway.

Secondly, no. If you put two beams together it will be as superposition of frequencies, not a single frequency, making up the final beam.

Lastly, I'll just reiterate one more time, color is not a frequency. Frequency is an abstract property of many physical quantities and in the electromagnetic spectrum, for a certain range of wavelengths, humans are able to make interpretations about the EM spectrum (in their eyes and brain) about frequencies. But you're "assuming the converse is true". It's similar with sound. Sound is just organism interpretation of pressure waves.

Of course, you probably also know that when you ring an A string on the guitar, the harmonic series also rings with. So even an instrument's single note is not a single frequency. We tune it by the "dominant frequency".

 

[FactChecker]

When we project two beams (red/green), the radiation from the screen toward the eye has a definite frequency or not?, if we detect it not by the eye but by an instrument is that 580 nm ?

No. A prism or spectrograph will show two distinct frequencies. There is no way that two different frequencies can merge into one pure frequency. The two frequencies may fool the eye and the eye / mind interpreters it as one color. But the standard physics instruments will know the difference.

 

[sophiecentaur]

Rather than doing as I suggested and actually reading the recommended links in this thread, bobie seems to be repeating, more or less, the same question again and again, despite the repeated answers he's been getting. Perhaps he hopes that the answer will change eventually to the one he thinks is true.

 

[OmCheeto]

Rather than doing as I suggested and actually reading the recommended links in this thread, bobie seems to be repeating, more or less, the same question again and again, despite the repeated answers he's been getting. Perhaps he hopes that the answer will change eventually to the one he thinks is true.

Well, this thread does remind me a bit of the blind men and the elephant parable.

(Four PF physicists, one PF neuroscientist, one PF newbie, and one PF amateur(me), all try and answer the question: "what is color/colour"?)

hmmm...

I've never heard this version:

Six blind elephants were discussing what men were like.
After arguing they decided to find one and determine what it was like by direct experience.
The first blind elephant felt the man and declared, 'Men are flat.'
After the other blind elephants felt the man, they agreed.

Moral:

"We have to remember that what we observe is not nature in itself, but nature exposed to our method of questioning." - Werner Heisenberg

Green is like my bank account, as it is the color of my money.
American paper money is all colored green, for some reason.
And why is that?
A money factory has the answer: "...because pigment of that color was readily available in large quantities..."

 

[sophiecentaur]

Well, this thread does remind me a bit of the blind men and the elephant parable.

(Four PF physicists, one PF neuroscientist, one PF newbie, and one PF amateur(me), all try and answer the question: "what is color/colour"?)

hmmm...

I've never heard this version:



Green is like my bank account, as it is the color of my money.
American paper money is all colored green, for some reason.
And why is that?
A money factory has the answer: "...because pigment of that color was readily available in large quantities..."

So what is the wavelength of a $10 bill?

 

[OmCheeto]

so what is the wavelength of a $10 bill?

500 +/- 10 nm, according to my eye, brain, and dictionary.

 

[bobie]

Thank you all, folks, for your response and the interesting discussion, I am really grateful for your efforts. It helped me understand a lot of things.

Just one word to clarify that I was not repeating the same question in order to get a desired answer, I do not think any answer is true. As a matter of fact in the OP I offered a wide range of possibilities, I was only trying to understand and trying to make myself understood, and probably did not succeed in both efforts,
I still do not understand this:
in life we mostly experience combinations of sounds or notes (chords, diminished fifth etc) and of light frequencies, true, but a tuning fork, (when the overtones die out) gives a pure frequency and we call it A-something or whatever and so on.
Why can't we apply the same scientific method and say that 580 nm is yellow-something or whatever, and 675 nm is red-whatever and 689 is a hue-of-red, and so any wavelength between 600 and 750 nm??
Is any combination of frequencies outside that range ever called red?
why for light frequencies we must necessarily talk of sensations?
why can't we say that when we interpret a combination of "685 and 540 nm" (red and green ) frequencies as "580 nm" (yellow) is just an optical illusion?
The elephant flattens the man , the mind does not alter the frequencies but only interprets them in a different way

If you indirectly answered these questions I regret overlooking it. If I cannot express my thoughts, my bad!
Thanks again

 

[sophiecentaur]

Thank you all, folks, for your response and the interesting discussion, I am really grateful for your efforts. It helped me understand a lot of things.

Just one word to clarify that I was not repeating the same question in order to get a desired answer, I do not think any answer is true. As a matter of fact in the OP I offered a wide range of possibilities, I was only trying to understand and trying to make myself understood, and probably did not succeed in both efforts,
I still do not understand this:
in life we mostly experience combinations of sounds or notes (chords, diminished fifth etc) and of light frequencies, true, but a tuning fork, (when the overtones die out) gives a pure frequency and we call it A-something or whatever and so on.
Why can't we apply the same scientific method and say that 580 nm is yellow-something or whatever, and 675 nm is red-whatever and 689 is a hue-of-red, and so any wavelength between 600 and 750 nm??
Is any combination of frequencies outside that range ever called red?
why for light frequencies we must necessarily talk of sensations?
why can't we say that when we interpret a combination of "685 and 540 nm" (red and green ) frequencies as "580 nm" (yellow) is just an optical illusion?
The elephant flattens the man , the mind does not alter the frequencies but only interprets them in a different way

If you indirectly answered these questions I regret overlooking it. If I cannot express my thoughts, my bad!
Thanks again

This is the question that you have been asking all along (in various terms). Your problem is one of definition and notation. Have you actually looked at the CIR colour diagram? How are colours specified on it? You will notice that it is a two dimensional graph so how, in the world, could you expect to be able to give the result of mixing a number of different coloured lights in terms of one number? You have been told several times, on this thread, that you cannot generate one wavelength of visible from two other wavelengths. You do not seem to have accepted that.

The wavelengths of the spectral colours are marked along the upper curve and they only refer to points on that actual curved line they are not like times on a clock face, that indicate the angle of the hands. None of the colours on a radius from White to a spectral colour, consist of just one wavelength of light. They are all produced by a mixture (desaturated) and many of them are named blue, green, yellow etc.. The large area of colour underneath the white point, represents perceived colours that do not relate to any spectral colour (single wavelength).

Virtually no one in the 'colour business' (artists, printers, TV directors, dye makers) concerns themselves with wavelength. They are interested in the colour that will be perceived by the viewer. What 'colour' would you call your favourite red jacket? It will be reflecting a significant amount of shorter visible wavelengths, too. If you insist that 'reds' can only be spectral then you jacket cannot be red.

Bear in mind that no one ever saw spectral red or green or yellow whilst the language of colour was developing, hundreds of years ago. It is only recently that the 'saturated' (pure spectral) colours were ever seen at all.

We're not talking about and "optical illusion"; we are talking about the normal way we perceive things. We can measure wavelength perfectly. We can predict, to some extent, what 'colour' a given combination of monochromatic light sources will be perceived as. But the perceived colour and the degree of agreement between different people cannot be predicted because the colour is in each or their heads.

I suggest you read all that - and what other people have written in the state of mind that will accept what is actually written and not insist on your particular interpretation of it. Saying you "don't understand" can sometimes imply that you "don't accept". I think that's what is happening. I strongly approve of your determination to get this stuff sorted in your head. You will get there if you just re-direct your efforts in the direction you are being pointed by the above posts.

 

[FactChecker]

Just one word to clarify that I was not repeating the same question in order to get a desired answer, I do not think any answer is true. As a matter of fact in the OP I offered a wide range of possibilities, I was only trying to understand and trying to make myself understood, and probably did not succeed in both efforts,

Your question was good. And you probably understand the answer better now than 99% of people.

why can't we say that when we interpret a combination of "685 and 540 nm" (red and green ) frequencies as "580 nm" (yellow) is just an optical illusion?

A physicist would. An artist would not. A physicist defines yellow as a specific range of frequencies. Most other people (artist, photographer, TV screen designer, etc.) define yellow as a mixture of red and green. The fact that a mixture of red and green did not create the single frequency of yellow was a startling realization to me several years ago. That is never mentioned except by a physicist. I would guess that other people don't know and don't care. But it does explain why 4, 5, and 6 color printers make better color photographs than a 3 color printer. They allow a more pure (requiring less optical illusion) yellows, along with other colors.