Maybe Mr. Briggs can help me out with the answer to this -- why do colors have the home values they have at maximum chroma? Why does yellow look "bright," red less so, and blue dark?
I did an experiment of trying to put the spectrum colors in order of value, and I got a series which went something like this:
yellow - green - cyan - orange - magenta - red - violet - blue
I just don't understand the physiology or physics of why each color has this seemingly inherent value property.
This is related to another question: I recently read this book on color theory by Jose Parramon. In it, he says that blue is found in all shadows. He says that blue is an inherent property of low-light conditions. For some reason this seems...not right.
In the case of natural light, there's blue-hued skyglow which provides secondary illumination against yellow-tinged sunlight. At dusk, I always thought the blue tinge was just the colored skyglow remaining as the sunlight decreased.
But I just have trouble believing that blue is always included in shadow color. The shadow color is a lower value of the local, sure, and also a lower value of the complement of the light color. But am I missing some important element of optics where blue always happens, no matter what?!
If you were in a red room illuminated by a white light, the shadows would have a reddish cast for the same reason.
From Gegarin's point of view
Color is wavelengths of light. The colors that you see are from light reflected off an object into your eyes. Just about everything absorbs light energy as heat. What is not absorbed is reflected. So the colors that you see an object is, is the wave lengths of light that are least absorbed by that object.
I believe it's to do with the sensitivity of our eyes to different wavelengths. We have R G and B receptors. Yellow light is stimulating R & G receptors, combined there are more R & G than B receptors, so we are more sensitive to that wavelength.
As a rule of thumb, green contributes roughly twice as much 'value/brightness' as red, which contributes about 4x as much as blue.
I think. I'm no optomologomatrician. The brain probably does all kinds of normalisation and compensation before you experience the colour anyway.
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...Just think of how blue appears brighter at dusk.
From Gegarin's point of view
Yellow and greens are at the middle of the visual light spectrum. The problem with color theory and artists is that it bounces back and forth between Optics and Aesthetics. Physically, yellow and green are in the middle. As you move towards red or blue you're "exiting" the band of electromagnetic radiation humans can detect with their eyes. That's probably why yellow seems brighter, it's around the peak of light we can experience. That translates into values when you're painting.Why does yellow look "bright," red less so, and blue dark?
In it, he says that blue is found in all shadows. He says that blue is an inherent property of low-light conditions. For some reason this seems...not right.
If you're going to paint a subject outdoors on Earth, that's just about right. Again, it's halfway between actual phenomena and perception. The blue light from the sky does effect places where direct light from the sun is blocked. But it's really subtle and how much you exaggerate it depends on your preference. Shadows are supposed to naturally lose chroma since you can't have color without light. Less light, less chroma. Don't take that as a rule though. I'm just speaking in terms of the physical. In a place with no ambient light from the sky, the shadow color would depend on reflected light and what kind of art you're making. You can always add complementary colors to shadows if you want. I'm pretty sure there's a whole movement of art related to playing with color and light and disregarding photorealism.
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If you are asking why are high-chroma blue objects relatively dark, the value that high-chroma colours of any given hue reach depends on:
1. How big a chunk of the spectrum can combine to still give a reasonably saturated light of that hue? (more for additive secondaries)
2. How strongly does that particular chunk of the spectrum affect the human brightness response? (the highest response is in yellow green; the lowest is at the extremes, where the spectrum fades to invisibility).
3. How close do actual materials get to reflecting most of that chunk, and little of the rest of the spectrum?
Yellow beats blue on all three counts. I've actually just added a new page talking about this on my website this week:
(Number 2 is the reason if you are talking about lights).
If I take your meaning correctly, if such a paint existed, it would appear very low in value because the amount of reflected light would be greatly reduced relative to the source light. The additive "boost" of the red and green wavelengths being bounced/mixed/reflected contributes to the overall luminosity of those pigments, correct?
As for issue #2 of the human brightness response -- do the edge fade out because they're just (for whatever evolutionary reason) on the borders of what we're able to perceive at all? For instance, in the case of additive color, if I have two squares on an RBG display, one at "B:255" and the other at "G:255", the blue square will have a lower value because the wavelengths which make up that blue include some which are outside the range of the visible spectrum? And the green looks lighter because its ingredient wavelengths are comfortably within our visible range? Do I have it right?
Yes you understand my point about yellow!
On the second question, I hope you're wrong about the blue square, because that would mean that it is bombarding us all with ultraviolet radiation! I think the wavelengths are mostly or entirely within the visible range, but in a part that causes a weaker visual response than the middle part of the spectrum. Look at the diagram Normalised responsivity spectra of human cone cells on this page linked to by Elwell:
This shows how each cone type responds most strongly to a peak wavelength, and its response falls off in either direction in a bell-shaped curve. Our perception of brightness seems to depend on the combined L+M response, with little or no input from the S cones. (I've seen it suggested that this is because there are fewer S cones, but I'm not sure that this is actually established).