What is the Definition of Color According to the CIE?

[bahamagreen]

Let's be clear about any sense of physical frequency with respect to neural function and perception.

The fastest speed at which neural membranes can depolarize ("fire") and wait out their refractory period (recovery until possible to fire again) allows a top firing rate of about 1000 Hz. There are no neural signal rates faster than that, most are slower.

Physical frequencies of light are NOT being sensed whatsoever.

Retinal molecules (pigments) are "unbleached" using energy into a bent (cis) shape. They are cocked like a spring waiting to be released. When a photon is absorbed at the 11-cis-retinal chromophore (the "spring release trigger"), that 11-cis state changes shape back to all-trans. This is called "bleaching" of the pigment. Individually, that is not enough to initiate anything... it take about 6 photons being absorbed close together at about the same time for the retinal molecules involved, residing within in a disc-like wafer, these discs stacked in the cones, to kick up enough activity to initiate a depolarization. It is the specific protein bound to the chromophore that determines what frequencies will be absorbed. The signal from the cone only indicates, "some photons were absorbed"...

 

[bobie]

After more than 80 posts you are still claiming that we see "frequencies.

I said "interpret".

 

[FactChecker]

The CIE 1931 color space is mathematically calculated by combining single-color spectral colors. It is exactly the mathematical definition that I have said is preferable to defining colors by a sensory perception. But it does use weighting functions that represent the "standard observer". That is both a blessing and a curse. It makes it easier to understand how the color will be seen by the "standard observer" and it formally defines the "standard observer" but it makes it dependent on that definition, and therefore debatable. Other CIE versions use other weighting function definitions of the "standard observer". Defining colors by perception is like saying "I can't tell you what it is, but I know it when I see it".

The most saturated red, green, and blue are spectral colors. Experiments have shown that people can tell the (sometimes subtle) difference between the saturated spectral colors and colors made from mixed primaries. The saturated spectral colors are not included in common color spaces like Adobe RGB, CMyk, and sRGB.

P.S. We cannot see the CIE 1931 color space on computer monitors. Monitors can only show the subset of colors in its smaller color space. You have to purchase sheets to see the real thing.

 

[FactChecker]

But the CIE chart only shows the outputs of three filters. The mapping is only one way. Two (three) numbers cannot describe the detailed received spectrum. I think the word for this could be degenerate. CIE doesn't do any better than your brain, in any meaningful way.

The CIE 1931 color space includes all the visible spectral colors. The color spaces build from the three primary colors (Adobe RGB, sRGB, etc) are subsets. Even the three primary colors used in those smaller color spaces are not the fully saturated colors in CIE 1931.

 

[sophiecentaur]

What is really "green"?

The CIE 1931 color space includes all the visible spectral colors. The color spaces build from the three primary colors (Adobe RGB, sRGB, etc) are subsets. Even the three primary colors used in those smaller color spaces are not the fully saturated colors in CIE 1931.

I'm not sure whether you are disagreeing or agreeing here.

 

[dauto]

The CIE 1931 color space is mathematically calculated by combining single-color spectral colors. It is exactly the mathematical definition that I have said is preferable to defining colors by a sensory perception. But it does use weighting functions that represent the "standard observer". That is both a blessing and a curse. It makes it easier to understand how the color will be seen by the "standard observer" and it formally defines the "standard observer" but it makes it dependent on that definition, and therefore debatable. Other CIE versions use other weighting function definitions of the "standard observer". Defining colors by perception is like saying "I can't tell you what it is, but I know it when I see it".

Yes that's exactly right. color is defined by perception which makes it a hard to pin point concept. It is what it is. It is not good enough for more analytical purposes and that's why physicists rely on spectrograph, not just color. No matter how you slice it, color is entangled with the human eye and brain perception process. Pretending it to be otherwise doesn't help anything.

 

[sophiecentaur]

Human sensory perception is not a good basis for a definition. We do not define speed by how tired we get running that fast. We do not define weight by how much it hurts to lift something. We do not define hardness by how it feels to get hit by something. Those may have motivated the concepts for primitive man, but they are not satisfactory for the modern world. All of those have better definitions that are widely accepted. Color is the same.

On the planet zog, they could be using exactly the same data for working out speeds, masses etc. All they would need to have done is what meteorologists do (or aim at doing) on Earth - namely to base units on things like light speed and carbon atoms. There is no way that we could expect the Zogians to have an identical CIE chart because it is entirely the result of phychophysical measurements using Humans with human eyes. Each sighted animal on Earth would have a different version of a CIE chart, too - if you could invent suitable tests. That makes Colour fundamentally different from your other examples of quantities. Colour is not the "same".

Edit: the CIE chart was not "mathematically calculated" from measurements. It was derived from many subjective tests.

 

[sophiecentaur]

I said "interpret".

Fair enough - but it isn't just "frequencies" when we see a colour; it is the weighted sum of the components that counts - a suitable term would be 'spectrum'. That one word of yours suggests that you are still not getting an important point. (Several other members have commented on this.)

 

[sophiecentaur]

@Factchecker

P.S. We cannot see the CIE 1931 color space on computer monitors. Monitors can only show the subset of colors in its smaller color space. You have to purchase sheets to see the real thing.

The "real thing" does not exist. You cannot produce spectral colours with pigments, although it is true that you can get more saturated colours with gels than with (standard) phosphors. The saturation is achieved at the expense of Luminance. The only "real thing" would have to consist of an array of numerous phosphors and a set of monochromatic sources along the curve.

The Pantone colours are 'standard' colours for dyes and they are accurately specified. However, they do not cover the whole CIE gamut. Any chart or card you could buy would need to be illuminated with the appropriate illuminant, of course, before you could rely on it.

 

[Pythagorean]

In pigments, I assume, a lot of the color comes from diffusive reflection and refraction throughout the material, leading to a lot more blending and chromatic dispersion as compared to a source like phosphors?

 

[sophiecentaur]

It comes mainly from the fact that a dense medium has very broad band reflection/transmission characteristics. Overlapping two passbands by a small amount will exclude most of the incident light but what gets through can be narrow band but low luminance. Under exposed colour prints tend to have saturated colours due to the non linearity of the sensitivity curves.
A transmission filter is much much better than a reflective surface due to the reasons you give although viewing a single coloured card under totally white light would be immune to corruption. Gloss finish photos tend to have 'deeper' colours under the best (non specular) lighting.

 

[FactChecker]

The various CIE color spaces introduce a variety of human "standard observer" weighting functions. But that is not to define colors. It is to define the perception of a human "standard observer". What about other animals like a bird or a bee? The CIE is meaningless for them. Does that mean color does not exist for them and only exists for a human? That is nonsense. The spectral density of light is universally accepted in physics and it says nothing about a "standard observer". That is the legitimate definition of colors. Colors are independent of who or what is observing it, be it a man, a bird, or a photocell.

 

[Dale]

This thread is long since started going in circles. Color is perceptual, frequency is physical. End of story.

Human sensory perception is not a good basis for a definition.

It is a perfect basis for terms pertaining to sensory perception. Human sensory perception exists and we need to define words used to talk about it. So obviously some definitions must be based on human sensory perception.

Color is a perceptual concept, not a physical one. On PF we don't get to redefine standard terms simply because we don't like the standard definitions. Regardless of your preferences the CIE is the standard-setting organization and their definition of color is authoritative.

Thread closed.