Color theory question ….

(Wdflannery) wrote:

Here is what I don’t understand …how is it that you can, as I understand, choose 3 primary colors….. and mix them to get any color at all ?????

In very simple terms, the frequency of the light reaching the retina is perceived as a specific color. It isn’t that colors are somehow being mixed in the waves, it’s that the eye is perceiving a very narrow range of EM energy as a color. Shift the frequency slightly, and the perceived color changes. The human eye is capable of distinguishing tens of thousands of different frequencies (colors).

The "primary colors" are something of an abstraction used by various human endeavors to make synthesis of the full spectrum of colors simple. Instead of having to have a phosphor that reacts precisely to every wavelength (color) of light, you measure the RGB values of the light at that point, and use the values to synthesize an equivalent color value. At output, instead of having a phosphor that can produce any color in the spectrum, you use the simpler technique of combining the RGB components to produce what the eye perceives as a dot of a particular color.

The notion of light being sine waves like sound is not quite accurate. Remember that photons show the characteristics of both waves and particles – and I’m not sure it’s been established exactly how the retina responds to these varying frequencies and perceives them with such fine differentiation.

—
| James Gifford * FIX SPAMTRAP TO REPLY |
| So… your philosophy fits in a sig, does it? |
| Heinlein stuff at: www.nitrosyncretic.com/rah |

On Fri, 09 Jan 2004 03:35:37 GMT, James Gifford
wrote:

(Wdflannery) wrote:

Here is what I don’t understand …how is it that you can, as I understand, choose 3 primary colors….. and mix them to get any color at all ?????

There is no one-to-one correspondence between sound and light. They are not the same thing. Do not even consider them together. Sound at its basic unit is simply particles of matter coliding against each other. When we hear a violin, we are perceiving a rhythmic pattern of the air hitting our ear drum. Sound cannot move through a vacuum. Light can. Light is an actual physical entity (albeit one that is still not fully understood by even top physicists — read what string theorists have to say about light if you really want to get freaked out).

— JC

"Wdflannery" wrote in message

This is something that puzzles me ….. I understand sound theory pretty well… and we know sound is vibrating air ….for pure tones the air

pressures

varies as a sine wave…. and, color is a vibrating electromagnetic field …..again with pure colors represented by sine waves …..
Here is what I don’t understand …how is it that you can, as I

understand,

choose 3 primary colors….. and mix them to get any color at all ?????

It

seems quite unlikely …. for example…. when three sinewaves of

different

frequencies are added, the result is not a pure sinewave at a different frequency …. suggesting to me that you can’t generate the pure colors,

much

less all the colors.

It’s a matter of the neurophysiology of color perception. The retina contains
three kinds of color receptors, which you can think of as outputting something very roughly like an RGB color space. As the nerve impulses travel towards the brain, they get transformed into something very roughly like LAB space. Further on, many more complicated transformations are performed that some people spend their whole lives trying to understand, with limited success. But the fact that 3-dimensional color spaces like RGB and LAB work is based on the the three kinds of color receptors. There are other species with either more or fewer than three kinds of color receptors; if they had invented printing and computers, they would have used color spaces with more or fewer dimensions.

Sound receptors in the ear are totally different, since there are receptors for many different wavelengths of sounds. Therefore, the perception of sound cannot be reduced to a low-dimensional space.

Wdflannery wrote:

This is something that puzzles me ….. I understand sound theory pretty well… and we know sound is vibrating air ….for pure tones the air pressures varies as a sine wave…. and, color is a vibrating electromagnetic field …..again with pure colors represented by sine waves …..
Here is what I don’t understand …how is it that you can, as I understand, choose 3 primary colors….. and mix them to get any color at all ????? It seems quite unlikely …. for example…. when three sinewaves of different frequencies are added, the result is not a pure sinewave at a different frequency …. suggesting to me that you can’t generate the pure colors, much less all the colors.

And, no one would suggest that you can take 3 pure (sound) tones and generate all the pure tones, much less all the sounds ….. so, what is it about light that is different from sound .. ?????

Is there any easy explanation ???? Or a link I could check, to relieve my bafflement????

Here is the way I see it.
A plucked string, for instance, causes a single frequency (say 1000 Hz) plus a few overtones (2000, 3000…..N)at much reduced intensity. There are no intermediate frequencies say, 1018 Hz or 1759 Hz. So basically we do no have a CONTINUOUS spectrum of frequencies. Even if we pluck 3, 4, 5 strings we will get discrete frequencies and their overtones, PLUS their sum and difference frequencies. But still not a continuous spectrum of frequencies.
Perhaps if you plucked a thousand different strings simultaneously, you would get enough fundamentals, overtones and sum / difference frequencies interacting that we would get something akin to "WHITE NOISE"
With Light, however, when we refer to e.g., "RED" light, we mean we get a CONTINUOUS spectrum of frequencies with a gaussian distribution from about 600-750 nm. "GREEN" may mean a similar continuous frequency distribution around 500-650 nm. Similarly "BLUE " means a continuous distribution around 400-550 nm. So any color, say orange (610 nm) is present in what we call RED. It is also present in what we call GREEN.
By mixing equal amounts of RGB we get a continuous spectrum that contains every conceivable frequency in the Visible range. We call this "WHITE LIGHT". By mixing various amounts of RGB we get different hues of color.
If we used equal amounts of pure MONOCHROMATIC laser light at say 680.00 nm (Red), 525.00 nm (Green), and 470.00 nm (Blue), we would not get white, because the combination does not contain ALL frequencies in the visible spectrum. I won’t even go into how the retina and the brain convert this information into the perception of color.
Bob Williams

"Robert E. Williams" wrote in message

…
With Light, however, when we refer to e.g., "RED" light, we mean we get a CONTINUOUS spectrum of frequencies with a gaussian distribution from

about

600-750 nm. "GREEN" may mean a similar continuous frequency distribution

around

500-650 nm. Similarly "BLUE " means a continuous distribution around

400-550 nm.

So any color, say orange (610 nm) is present in what we call RED. It is

also

present in what we call GREEN.

This may or may not be the case. What we perceive as red light may have a very narrow or a moderately broad range of frequencies.

…
If we used equal amounts of pure MONOCHROMATIC laser light at say 680.00

nm

(Red), 525.00 nm (Green), and 470.00 nm (Blue), we would not get white,

because the

combination does not contain ALL frequencies in the visible spectrum.

If the intensities are balanced properly, it will in fact be perceived as white.

On 09 Jan 2004 03:21:13 GMT, (Wdflannery) wrote:

This is something that puzzles me ….. I understand sound theory pretty well… and we know sound is vibrating air ….for pure tones the air pressures varies as a sine wave…. and, color is a vibrating electromagnetic field …..again with pure colors represented by sine waves …..
Here is what I don’t understand …how is it that you can, as I understand, choose 3 primary colors….. and mix them to get any color at all ????? It seems quite unlikely …. for example…. when three sinewaves of different frequencies are added, the result is not a pure sinewave at a different frequency …. suggesting to me that you can’t generate the pure colors, much less all the colors.

And, no one would suggest that you can take 3 pure (sound) tones and generate all the pure tones, much less all the sounds ….. so, what is it about light that is different from sound .. ?????

Is there any easy explanation ???? Or a link I could check, to relieve my bafflement????

Other than acoustic waves that (mechanically) interfere with each other in the transport medium lightwaves do not interact.

The human eye responds to certain frequencies of light and most of the color impression is created in your brain as a result of amount and intensity of only three major areas of frequence in the range of red, green and blue.

That the frequencies are still available separately can be checked using different laser colors (with a very narrow bandwidth) on one end and a prisma on the other end – there is no modulation of frequencies and demodulation.

Michael

(Wdflannery) wrote:

This is something that puzzles me ….. I understand sound theory pretty well… and we know sound is vibrating air ….for pure tones the air pressures varies as a sine wave…. and, color is a vibrating electromagnetic field …..again with pure colors represented by sine waves …..

It’s quite simple, you may learn about it at:
http://www.bradford.ac.uk/acad/lifesci/optometry/resources/m odules/stage1/pvp1/Colour.html

HTH 😉
Peter

Wdflannery wrote:

This is something that puzzles me ….. I understand sound theory pretty well… and we know sound is vibrating air ….for pure tones the air pressures varies as a sine wave…. and, color is a vibrating electromagnetic field …..again with pure colors represented by sine waves …..

Yes, there are many useful analogies between sound and light. Both are wave energy phenomena, and both have the concept of mixed frequencies.

Here is what I don’t understand …how is it that you can, as I understand, choose 3 primary colors….. and mix them to get any color at all ????? It seems quite unlikely …. for example…. when three sinewaves of different frequencies are added, the result is not a pure sinewave at a different frequency …. suggesting to me that you can’t generate the pure colors, much less all the colors.

Your intuition is accurate. It’s not possible to generate all the colors from three primaries, but you can generate a good approximation, and let the eye, which is very good at this, put the pieces together into something reasonable.

And, no one would suggest that you can take 3 pure (sound) tones and generate all the pure tones, much less all the sounds ….. so, what is it about light that is different from sound .. ?????

The difference is between the eye and ear, more than between sound and light. Where the eye merges three frequencies of light into a single color, the ear will hear a chord when three frequencies are present

You can fool the eye into thinking a particular frequency is present by using the correct ratio of red, green, and blue, as well as create new colors between red and blue that don’t exist in the spectrum. The ear is smarter in this regard in that it takes all the frequencies apart instead of lumping them together, so you hear chords.

This is because the eye uses just three overlapping detectors that are sensitive to red, green, and blue. The ear uses an array of thousands of hair cells, each tuned to a slightly different frequency, to extract more information from the perceptual mix than the three detectors in the eye are able to.

The ear works like a spectrophotometer and the eye is more like a colorimeter.

Of course, the ear has an easier job, since it doesn’t have to create and interpret an acoustical image based on the sound reflecting from the objects around you. Experiments with acoustic holograms have been done, and in the natural world, bats and owls, do some of this.

You could conceivably build a smarter eye in the form of a digital camera that gathers complete frequency information at each and every pixel – maybe this will happen some day. For now the technology isn’t there, and our cameras use mixed arrays of sensors that are filtered for a relatively small number of colors, very similar to the way the eye works.

Is there any easy explanation ???? Or a link I could check, to relieve my bafflement????

Everything you need is right here in c.g.a.p 🙂

Take care.
—

Mike Russell
www.curvemeister.com
www.geigy.2y.net

"Wdflannery" wrote in message

[…]

Rather than trying to explain it, may I suggest a rather enlightening and fun read? "Vision and Art: The Biology of Seeing" by Margaret Livingstone. Note the "biology" aspect. We perceive color in terms that the physics doesn’t address in the pure abstract.

"James Gifford" wrote in message

(Wdflannery) wrote:

[…] and I’m not sure it’s been established exactly how the retina responds to these varying frequencies and perceives them with such fine differentiation.

Recent literature which covers the physiology of the eye does a very good job of describing how the normal human eye perceives color. How the eye works is astonishing, and to learn how it cannot see certain colors is equally surprising.

"Robert E. Williams" wrote in message

Here is the way I see it.
[…]
With Light, however, when we refer to e.g., "RED" light, we mean we get a CONTINUOUS spectrum of frequencies with a gaussian distribution from

about

600-750 nm. "GREEN" may mean a similar continuous frequency distribution

around

500-650 nm. Similarly "BLUE " means a continuous distribution around

400-550 nm.

So any color, say orange (610 nm) is present in what we call RED. It is

also

present in what we call GREEN. […]

Keep in mind that the normal human eye sees _certain_ colors which exist at near-opposite ends of the true spectrum as the same color.

"Xalinai" wrote in message

Other than acoustic waves that (mechanically) interfere with each other in the transport medium lightwaves do not interact.

Which is irrelevant to how the eye works. The eye infers color using rather fuzzy logic which depends upon a kind of interference.

The human eye responds to certain frequencies of light and most of the color impression is created in your brain as a result of amount and intensity of only three major areas of frequence in the range of red, green and blue.

Most of the color is made from signals in the eye. The brain cannot image what the eye does not first render.

That the frequencies are still available separately can be checked using different laser colors (with a very narrow bandwidth) on one end and a prisma on the other end – there is no modulation of frequencies and demodulation.

The human eye does not see all the colors in the so-called visible spectrum. There are areas of less and greater sensitivity. You might say the eye is hue-disadvantaged.

On Fri, 9 Jan 2004 12:04:57 -0600, "jjs" wrote:

"James Gifford" wrote in message

(Wdflannery) wrote:

[…] and I’m not sure it’s been established exactly how the retina responds to these varying frequencies and perceives them with such fine differentiation.

Recent literature which covers the physiology of the eye does a very good job of describing how the normal human eye perceives color. How the eye works is astonishing, and to learn how it cannot see certain colors is equally surprising.

And some animals have color perception that exceeds our own. Birds of prey, for example, have 4-color receptors instead of 3, thus adding a whole dimension of color discrimination (compared to human vision).

Amazing. Thanks to all. Great info.