Magenta is a mystery.

Have you ever had your head CAT scanned?

Well, I have. Once...

While I was lying there in the machine, very sick, very still, eyes closed, I "saw" a well defined horizontal line of some murky color or other move methodically (from top to bottom...I think it was...it was several years ago) across my "field of vision". I remember thinking, "that must be the X-rays 'exciting' some receptors on my retinas." I remember too, being mildly surprised that I could "see" anything in that region of the electro-magnetic spectrum. If I hadn't been so miserable, the experience might have unnerved--or intrigued--me....

You're probably already aware of this, but, magenta can almost be thought of as one of the rainbow colors, darkened. Or, if not exactly darkened, with white removed and the sign flipped. In particular, think of each color as an rgb vector. So if (0,1,0) is green, and (1,1,1) is white, then -((0,1,0) - (1,1,1)) is (1,0,1), or magenta.

The limitations of our color perception are quite fascinating. One thing to note is that in principle, colors are waveforms with all the complexities and overtones of sonic waves --- we just don't perceive them. So if we had sufficiently fancy eyes, we could see the timbre of colors much as we hear the timbre of note. Sadly, all we really get are hue, saturation and intensity. As it is, we'll never see the difference between oboe-blue and violin-blue. Just plain old blue.

You're probably already aware of this, but, magenta can almost be thought of as one of the rainbow colors, darkened. Or, if not exactly darkened, with white removed and the sign flipped. In particular, think of each color as an rgb vector. So if (0,1,0) is green, and (1,1,1) is white, then -((0,1,0) - (1,1,1)) is (1,0,1), or magenta.

The limitations of our color perception are quite fascinating. One thing to note is that in principle, colors are waveforms with all the complexities and overtones of sonic waves --- we just don't perceive them. So if we had sufficiently fancy eyes, we could see the timbre of colors much as we hear the timbre of note. Sadly, all we really get are hue, saturation and intensity. As it is, we'll never see the difference between oboe-blue and violin-blue. Just plain old blue.

You seem to have a far-reaching mind. In this case, I would recommend the classic Art and Illusion by E. H. Gombrich.

Hey these "guys" work at Cal.
http://psyche.cs.monash.edu.au/psyche-index-v7.html#ib
or was that in the ago?

I'm as much interested in your conclusions about the quality of thought as the mechanics of vision. Let's think this through a bit. Stupidity and ignorance can leave us in the same mire of mistaken thought, but they are different. Ignorance is our normal state and so hardly to be condemned. Stupidity is another matter.

Ask yourself how much time you had devoted to the magenta issue. How intellectually devoted were you to the notion that magenta represented a narrow range of wavelengths? If you had based a great deal of other thinking on this, then it must be quite a shock to find that all that thinking is built on sand. That we might think of as stupid. If it was just one of the many assumptions we make on subjects about which we are not expert, well, the interesting thing is that self-comdemnation (even with a certain level of light-heartedness?) in your reaction. We all like our unconsidered notions to prove true. We probably all extend our intellectual pride somewhat past reasonable bounds (leaving us feeling embarrassed, so stupid, when found out). A quick tour around the world of web logs gives evidence of this. It's nice that we have the chance to enjoy these little information surprises on a regular basis.

Yeah…it's really interesting the way color perception works. A vivid yellow is two detectors firing, and it may be one wavelength of light doing that, or many. But magenta always has to be more then one wavelength of light, because, as you say, there is no one wave that will fire the two detectors at the ends of our range, without also firing the inner one.

I've painted in oils since I was a kid, and if you work with paint much, you get accustomed to thinking in terms of pigment, and spectrums which are weighted in this or that particular way. So Ultramarine Blue (which was once upon a time made from crushed lapis lazuli, and is now commonly made by a furnace process of clay, soda, sulfur, and coal) is different from Cobalt Blue (cobalt oxide and aluminum oxide), because of their different spectrums. Burnt Umber (calcined iron oxide plus manganese dioxide) isn't any more a color then Magenta, but when you've worked with it a while you come to know that particular aggregate of waves by that name, even when it's not the result of that particular pigment. Magentas are like that. Just with a U shaped spectrum.

Once I worked as a architectural model maker, and what I often found particularly tricky was duplicating someone's gray, when modifying an existing model. After a while you get good at looking at a gray, and seeing how much green is in it for example, or blue, and you can make a reasonable guess at which particular set of pigments the previous model maker used to reach that specific gray. Duplicating grays was the real test of how well my eyes were working that day.

Watching the sky change throughout a day has been a pleasing thing for me since I was a kid. Learning over the years how atmosphere and sunlight and the spinning earth produce and change the blue that I see has only deepened it. There's actually a lot of color in there, and when you get a good cloud deck at twilight there is nothing like watching it all go through its changes.

"Consider magenta"? Heck, consider brown.

"Seems to me I should learn a lot more about visual physiology, or is it physiological visuality?"

As odd as it sounds the actual name of the field you are looking for is Phychophysics! There are two realy nice chapters about the subject in the Feynman Lectures.

Cheers,

Psychophysics isn't quite what you're looking for. Psychophysics is about how to set up psychological experiments that yield quantitative results, using techniques like threshold detection, scaling, etc. Psychophysics is one of the tools in the toolbox of someone studying color vision.

The name of the fields you're really looking for are Vision Science and Color Science. Vision Science people are usually found in psychology departments, though UC Berkeley has a Vision Science program; there are also people who call themselves Color Scientists, and the difference between Vision Science and Color Science is where one looks: the vision scientist figures out how the human visual system works, the color scientist does more applied work (color reproduction, dye formulation, lighting, etc.)

I'm sure Rob meant to type: "psychophysics"

Brad, Berkeley has a multidisciplinary graduate program in Vision Science, you might want to look for a course on Visual Perception that you could sit in on (or at least bug the instructor with an e-mail or two). The people looking at questions most relevant to yours will likely be housed in the psych and neuroscience depts.

oops, your post wasn't up yet when I went to write mine Peter. Honest! :)

Sorry for the repetition.

Read The Natural History of the Senses (1990).

Well, I may be confused, but it seems to me that there is the potential pitfall of mixing perception with reality. Is it that there is anything like magenta or that the brain has a way of visually representing combinations of colors?

An interesting fact is that different cultures do not identify colors the same way. In Japan for example, "aoi" means blue but it ranges into some colors Westerners would classify as green. (e.g. Green lights in Japan are thought of as "aoi".)

On the other hand, can somebody be trained to recognize ultra-sounds? I can hear sounds that my cat reacts to but my better half cannot perceive. A large part of our perception is left "unoticed" because we have no incentive to spend our attention on it or there is no cultural filter through which we can classify it (perhaps because there are not enough individuals with the capacity to perceive these things to begin with.)

Also, I have very good odorate. Why? Well there is a tendency for people for people with a deficient sense to develop hyper-sensitive substitude senses. Experiment: try to block a dog's nastrils and ears (without getting it completely mad is the challenge) and observe its complete inability to orient itself...

Enough nonsense speculation %-)

There are obviously philosophical issues around how one really "sees" color, and whether what you think of as magenta is really what I see in my "mind's eye" or not.

However, the mechanisms at the retinal level are fairly well understood. Color vision is (to simplify a bit) created by having three different classes of photoreceptors (cones), usually called L, M, and S (long-, medium-, and short-wavelength sensitive). The spectral responses of these sensors, as a part of the whole visual system, have been known to a fairly high degree of accuracy for a long time. James Clerk Maxwell performed the first "color matching experiment" which is used to characterize the spectral response by matching a test light against a mixture of three colored lights (which can be spectral or not, doesn't matter). Do that enough times with enough different lights and you've characterized the whole system. Under constant viewing conditions, color matching is a linear system. The system of color measurement we use today was measured in the 1920s by Guild and Wright, and was standardized in 1931 (the "CIE" system). There have been some modifications to those data in the ensuing years, but only for special circumstances (larger fields of view)--the original data were quite good.

There are several sources I'd recommend for further reading. MIT Press did a two-volume set called Readings on Color. I have Vol. 2: The Science of Color, and it's a good collection of papers on the basics of color vision and colorimetry. Volume 1 is on Philosophy of color; I haven't read it. Foundations of Vision by Brian Wandell (published by Sinauer) is a good introduction to vision science, including color. Human Color Vision by Kaiser and Boyton is good if you want to go really deep into it.

Thinking about brown is an interesting case, because it can be a spectral color. Brown only exists in relation to other colors, usually a white--put a light bulb that you think of as "brown" in a completely dark room and you won't see brown, you'll see orange.

>>MIT Press did a two-volume set called Readings on Color. I have Vol. 2: The Science of Color, and it's a good collection of papers on the basics of color vision and colorimetry. Volume 1 is on Philosophy of color; I haven't read it.

"Philosophy of Color"? What could the "philosophy of color" possibly be?

Brad, doesn't the spectrum curve back upon itself at the point you're looking for? So R hits V at that point, and Magenta is somewhere in there.

Philosophy of color? There are questions that you can't answer with physiology or physics, at least not at the moment. Simplistic examples are questions like, what is green? Where does it exist? With color science you can say a material with a certain reflectance spectrum viewed under a certain illuminant with a certain surround looks green, and you can know whether it will look green in different circumstances, but that hasn't really told you much about green-ness, where green-ness exists, whether it's an absolute thing, whether my green is the same as yours, etc. The standard definitions of color in color science are essentially circular.

I seem to recall reading a short expository paper -- by Feynman, I think-- entitled: "Why Is There No Brown Light?"

Is this recollection in error ? If not, where can I find this article?

Thanks --

alfeld@twcny.rr.com