greg@endor.harvard.edu (Greg) (11/14/86)
As most of you know, the color "red" on a monitor is really some distribution of frequencies of visible light; i.e. when a red piece of phosphorous emits some amount of light at a wavelength of 2200 angstroms, some different amount at 2201 angstroms, and so on. Similarly, a red patch on color film reflects some known percentage of the incident light at a given frequency. Lastly, the red receptors in my eyes respond differently to different wavelengths. For example, I may see half as much red if my eye receives 1 unit of light at wavelength 2000 angstroms as I would see if my eye received 1 unit of light at 2200 angstroms. Does anyone have know (or have references to) the exact frequency profiles of red, green, and blue phosphorous on a color monitor, red, green, and blue film, and the red, green, and blue receptors in a person's eye? I realize that the characteristics of a color screen and film may vary with the brand, so I'll mention that I'm using a Sun-3 and Kodachrome film (ASA 100 or slower; I haven't bought the film yet). The film will probably be developed on Kodak paper. ---- Greg
spf@bonnie.ATT.COM (11/14/86)
From clyde!rutgers!seismo!husc6!endor!greg Fri Nov 14 09:58:22 EST 1986 Organization: Harvard >Does anyone have know (or have references to) the exact frequency profiles of >red, green, and blue phosphorous on a color monitor, red, green, and blue >film, and the red, green, and blue receptors in a person's eye? >Greg > You've fallen into a trap common to computer technologists and engineers: you've assumed that the eye and brain work like a computer. The cones in the eye's retina respond differentially to frequency of the incoming radiation. There are not three well-defined types of receptors which one would call red, green, and blue. Indeed, red, green, and blue refer to subjective color judgments, not absolutes. For a given individual you can measure the frequency's which they REPORT as red, green and blue, but they will be different for different folks. Enjoy! Steve
btb@ncoast.UUCP (Brad Banko) (11/16/86)
for questions about light and color, Eastman Kodak is probably the place to go... I would recommend that you contact them (Rochester, NY ?)... I understand that they take light and color very seriously (hope this is useful). -- Brad Banko ...!decvax!cwruecmp!ncoast!btb Cleveland, Ohio
john@frog.UUCP (John Woods, Software) (11/17/86)
>From clyde!rutgers!seismo!husc6!endor!greg Fri Nov 14 09:58:22 EST 1986 >>Does anyone have know (or have references to) the exact frequency profiles >>of red, green, and blue phosphorous on a color monitor, red, green, and blue >>film, and the red, green, and blue receptors in a person's eye? >>Greg > > > You've fallen into a trap common to computer technologists and > engineers: you've assumed that the eye and brain work like a computer. > The cones in the eye's retina respond differentially to frequency > of the incoming radiation. First, the cones individually do respond to particular bands of light preferentially (see articles in the past few months in SCIENCE and Scientific American), roughly centering on "red", "blue", and "green". However, perceiving color IS done differentially, and in Freshman Physics at MIT, we learned about this (I believe it was discovered by Edwin Land), and were given a demonstration: a black and white picture of a clown with brightly colored candy, taken with a blue filter, and the same picture taken without a filter (and, due to the characteristics of the film, having the strongest color sensitivity in the yellow area spectrum). When these two images were projected onto the screen, we saw full color (reds, greens, you name it), even though these colors weren't in either slide. It was stated (without demonstration) that you can get the same effect by making photos using the two yellow lines of sodium -- that tiny difference in frequency allows the brain to reconstruct the color of the actual image! -- John Woods, Charles River Data Systems, Framingham MA, (617) 626-1101 ...!decvax!frog!john, ...!mit-eddie!jfw, jfw%mit-ccc@MIT-XX.ARPA "Soylent Green is People Helping People!"
dan@rna.UUCP (Dan Ts'o) (11/20/86)
>From clyde!rutgers!seismo!husc6!endor!greg Fri Nov 14 09:58:22 EST 1986 >Organization: Harvard > >>Does anyone have know (or have references to) the exact frequency profiles of >>red, green, and blue phosphorous on a color monitor, red, green, and blue >>film, and the red, green, and blue receptors in a person's eye? >>Greg >> >You've fallen into a trap common to computer technologists and >engineers: you've assumed that the eye and brain work like a computer. >The cones in the eye's retina respond differentially to frequency >of the incoming radiation. There are not three well-defined types >of receptors which one would call red, green, and blue. Hmm... A bit of disinformation here... There, of course, ARE three well-define cone receptors as well as the rods. The spectral sensitivity of the cones DO peak in the red, green and blue. However, they are broadly tuned such that, e.g., a monochromatic green light will also excite (to a lesser extent) the red cones. This is as it should be, since three sharply tuned receptors would show nothing for light outside their bands, forcing the necessity for many more than three receptors. Yes, the beginnings of color vision is computed early on differentially. The concept is called color opponency. There are two major color opponent systems known: red/green and blue/yellow. There may also be a green/blue opponeny system. Yellow is thought to be derived from the summed inputs from red and green cones. However, color perception is much more complicated than that. One important property which indicates this is called color constancy. Color constancy is a high level computation performed somewhat more globally (in visual space.) It is manifest, e.g. in the relative invariance of the perceived color of a group of object, irrespective of the spectral content of the illumination. For example, things seem to have nearly the same color under a wide range of illuminations: dawn, dusk, midday, even under highly colored lighting. The point is, color perception is much more complicated than just detecting the wavelengths of light arriving at the retina. Back to the original question. The exact output of a color monitor is, of course, dependent on the phosphors that a monitor uses, among other things. There are quite a few phosphors available. The bottom line is that you need to find out what monitor you have and what options are on it (the most often distinction is between "standard" and long persistence phosphors) and then contact the manufacturer for the curves. Those companies well-based in the U.S. are usually more capable of answering the question. For example, I have the output curves for my Tektronics 690SR and a Conrac monitor. (If you're just curious, I could perhaps describe them to you by email.) As far as the spectral sensitivity of the human cones, there are numerous references and methodologies. The most classical studies just measured via microspectroscopy, the absorption curves of the cone pigments. Then there are psychophysical and physiological measurements. Most of the results from these methods coinside, though not completely. Perhaps the best place to start is a standard reference text on the retina (any decent science or medical library should have one). An example is, I believe, Retina by Rodieck. BTW, since when were computers able to "see" ? :-)
smolar@winston.UUCP (Stephan Smolar) (11/22/86)
Tests were done on the human eye for standards to be set for
color television phosphors bye the CIE (France) and the ICI
(US) International Commission of Illumination. The CIE is
recommended as standards by the Standards committee of the
Institute of Electrical and Electronics Engineers.
Results.
From the Wald and Brown (1965) experiments the three peak
sensitivies of the cones (color sensors are 450, 530 and 570
nanometers.
The CIE primaries are
Red: 700 nm
Green: 546.1 nm
Blue: 435.8 nm
The FCC phosphor Wavelengths are
Red: 610 nm
Green: 535 nm
Blue: 460 nm
I believe that each film in cameras had different pigments
and there is no standard set in stone. However of that I am
not sure.
Ref: Television Broadcasting by Harold E. Ennes
The Psychology of Visual Perception by R. Haber and M.
Hershenson
I hope this is of some help.
--
Stephan Smolar | ..decvax!microsoft!ubc-vision!winston!smolar
New Media Technologies Ltd. | ..ihnp4!alberta!ubc-vision!winston!smolar
(604) 291-7111 |kgd@rlvd.UUCP (11/22/86)
In article <647@husc6.HARVARD.EDU> greg@endor.UUCP (Greg) writes: > >Does anyone have know (or have references to) the exact frequency profiles of >red, green, and blue phosphorous on a color monitor, red, green, and blue >film, and the red, green, and blue receptors in a person's eye? I realize >that the characteristics of a color screen and film may vary with the brand so >I'll mention that I'm using a Sun-3 and Kodachrome film (ASA 100 or slower; I >haven't bought the film yet). The film will probably be developed on Kodak >paper. This problem is further complicated by the fact that the sensitivity of the three types of photopigment to wave-lengths of light in the human eye varies between individuals and with age. The best explanation I have seen was in a tutorial paper by Gerald Murch. His address is given as: Tektronix Inc, PO Box 500, Beaverton, Oregon 97077, USA. -- Keith Dancey, UUCP: ..!mcvax!ukc!rlvd!kgd Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX JANET: K.DANCEY@uk.ac.rl Tel: (0235) 21900 ext 5716
jbm@aurora.UUCP (Jeffrey Mulligan) (11/22/86)
> > Does anyone have know (or have references to) the exact frequency profiles of > red, green, and blue phosphorous on a color monitor, red, green, and blue > film, and the red, green, and blue receptors in a person's eye? I realize > that the characteristics of a color screen and film may vary with the brand, so The book "Color Science" by Wyszecki and Stiles is pretty much the "bible" of color vision; it contains, among other things, the action spectra of the three cone mechanisms. For many purposes, it is more convenient to describe a color by its effect on the cones rather than by the complete spectrum, since many different spectral distributions will be visually indistinguishable ("metameric matches"). The most commonly used system is CIE (a French acronym for the society that maintains the standard). Some manufacturers (such as Tektronix) give the CIE coordinates of the various phosphor options along with the other monitor specs; unfortunately, this is not true of many other monitors. To make matters worse, knowing the phosphor chromaticities does not tell you what you will get when you drive the red GUN, unless the purity adjustment is *perfect*. Jeff Mulligan