rickc@iddic.UUCP (08/06/84)
The nattering nit-nits of the net are at it again. :-) (A distinct species from the flamers, the nit-nits pick everything to death). >>Human eyes cannot generally see "chords" of light. >>Our ears are capable of doing a spectral analysis of sound, but we cannot >>do the same with light. The ears can simultaneously detect a large range of >>frequencies, our eyes can only detect (!) three. However, we are able to see >>one "chord", the combination of blue and red which makes magenta. >(Exclamation point mine) > > >The eyes also can detect (and discriminate) a large range of light frequencies >(from about 400 to 700 nm), not just three. Three light absorbing pigments >with different spectral sensitivities (broad, overlapping, but not identical >spectral sensitivities) report to the visual system the quantum catches >they receive from any light. The visual system compares their three outputs >to determine the "color" of the light. So the visual system >can discriminate any two single wavelengths in the visible spectrum >(except a pair very close together), but any two mixtures of wavelengths >that produce the same quantum absorption in the three pigments look identical. > Well, what I should have said is detect three frequencies SIMULTANEOUSLY. Obviously, I didn't mean that human eyes can only detect three different frequencies of light. I used the word simultaneously earlier in the sentence, and since I was drawing an analogy assumed that the reader would realize that I meant three SIMULTANEOUS frequencies. >I have no idea what to make of your use of the word "chord" with respect >to vision. If a chord is simply a mixture of wavelengths, than of >course we can _see_ them. Can we tell what the constituent wavelengths >are? No. In the case of magenta, we can tell approximately what two >wavelengths must be mixed to produce it, but only really on the basis of >empirical color mixture experience. It's not at all like what the ear >does, where the components of a chord are experienced as distinct in the >mixture. Magenta looks like a single color, not like the superposition >of two colors, red and blue. I'm truly sorry that you don't know what to make of my use of the word chord. I didn't mean a section of a circle (:-)). I tried to make an analogy to music, where a human can discriminate the the individual frequencies that exist within a chord. >I'm not at all certain that the author of the quoted lines >misunderstands color vision, As a matter of fact, I do understand color vision. Is this kind of comment necessary? >but I think that one could easily read what >he said and come away with some mistaken ideas of vision. I hope this >makes some of the processes clearer. I really can't say that 'report to the visual system the quantum catches they receive' is any clearer than what I said. My intention was not to go into the detail of human vision, but to make the point that I find to be an interesting realization: that the eyes can only detect three frequencies simultaneously, and what this implies. What would vision be like of we could see seven 'primary' colors? (that is, color receptors for those wavelengths or ranges of wavelengths) A hundred? Rick Coates tektronix!iddic!rickc
MJackson.Wbst@XEROX.ARPA (08/17/84)
Pretty touchy, aren't we? I thought that ihima!cmb's response to your original message was quite reasonable. If, as you say, you do indeed "understand color vision" then you should understand that it is not true that the human eye can only "detect three frequencies," "SIMULTANEOUSLY" or not. What is, of course, true is that the (normal) human eye seems to take three different weighted samples across the visible spectrum. Thus any color, whatever its spectral content, is describable by three "color coordinates," such as the hue, value (lightness), and chroma of the Munsell system. If you don't think your "three frequencies" statement is misleading then you know less about discourse than about color vision. Mark