miguel@aclcb.purdue.edu (Phillip) (03/23/91)
The additive primary hues, according to an undergrad general psychology
text book I have (Gleitmann (sp?)), are blue and yellow (which are
complementary) and red and green (complementary). Blue, yellow and green
all have a "unique" wavelength at which the human eye/brain percieves them
to be without tinges of any other color. Red is "extra-spectral" in that
it requires a combination of wavelengths to produce a "pure red"
sensation. The complementary hues when mixed in equal amounts produce
grey (i.e. blue + yellow = grey). The process is called "opponent-pair" or
something similar. Mixing (adding) non-complementary hues produces an
intermediate color (i.e. red + yellow = orange).
The subtractive primaries are different. Two pigments mixed together
only allow wavelengths neither absorbs to be reflected.
So how does a color TV work? I understand that it uses only red green
and blue and that red and green mixed together (and surely this would be an
additive process, not a subtractive one) produce yellow.
Does anyone know?
_ _
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with "John A. Doe" replaced by your name.Jenni Sheehey <JMS111@psuvm.psu.edu> (03/23/91)
In article <00945FE5.1F9B5480@aclcb.purdue.edu>, miguel@aclcb.purdue.edu (Phillip) says: > > The additive primary hues, according to an undergrad general psychology >text book I have (Gleitmann (sp?)), are blue and yellow (which are Great text book. I love it. =) > So how does a color TV work? I understand that it uses only red green >and blue and that red and green mixed together (and surely this would be an >additive process, not a subtractive one) produce yellow. > Does anyone know? This isn't my strong point, but I think I see where the confusion comes from. Additive mixing refers to light. Subtractive mixing refers to pigment/crayons/what have you. The additive primaries are red, blue, and green, while the subtractive primaries are red, blue, and yellow. The reason that the two type are named that way (I suppose) is that you are adding or subtracting the wavelengths that are being absorbed. The blue/yellow and red/green dichotomies are actually a facet of *vision* rather than light, referring to the two types of cones present in the retina. (That's why a person who is red/green colorblind can often still see blue, etc.) Anyway, the end result of all this is that TV works additively, with the blue and green light combining to form yellow. Disclaimer: All I have is a BA in Psych, and a bit of experience tutoring a course taught from the Gleitman, I'm not a PhD (like anyone would mistake me for one--ha ha) =). Besides, I bet even PhD's are wrong every once in a while. =) --Jenni /----------------------------------------------------------------------\ | Jenni Sheehey - JMS111@PSUVM.psu.edu BITNET/Internet | | Lab Attendant/Student Consultant | | "No, dear, you don't want those. Those are plus sizes. They're | | for people like your Aunt Sharon." --heard in a local Wal-Mart. | \----------------------------------------------------------------------/
jpab+@andrew.cmu.edu (Josh N. Pritikin) (03/23/91)
miguel@aclcb.purdue.edu (Phillip) writes: > The additive primary hues, according to an undergrad general psychology > text book I have (Gleitmann (sp?)), are blue and yellow (which are > etc... I suggest that you find a computer with a 24-bit color display and play with a color painting program for a couple of hours. Also note that color is just half the story, texture is very important in what we think of as color. joshp -> t
winalski@psw.enet.dec.com (Paul S. Winalski) (03/23/91)
In article <00945FE5.1F9B5480@aclcb.purdue.edu>, miguel@aclcb.purdue.edu (Phillip) writes: |> The additive primary hues, according to an undergrad general psychology |>text book I have (Gleitmann (sp?)), are blue and yellow (which are |>complementary) and red and green (complementary). Blue, yellow and green |>all have a "unique" wavelength at which the human eye/brain percieves them |>to be without tinges of any other color. Red is "extra-spectral" in that |>it requires a combination of wavelengths to produce a "pure red" |>sensation. The complementary hues when mixed in equal amounts produce |>grey (i.e. blue + yellow = grey). The process is called "opponent-pair" or |>something similar. Mixing (adding) non-complementary hues produces an |>intermediate color (i.e. red + yellow = orange). |> The subtractive primaries are different. Two pigments mixed together |>only allow wavelengths neither absorbs to be reflected. |> So how does a color TV work? I understand that it uses only red green |>and blue and that red and green mixed together (and surely this would be an |>additive process, not a subtractive one) produce yellow. |> Does anyone know? I'm not an expert in retinal physiology and biochemistry, but here's my recollection of the mechanism. There are several (three major ones, I think) photochemically active pigments in the cone cells of the retina (the ones responsible for color vision). Each pigment molecule is capable of absorbing light quanta, which cause it to eject an electron and thereby change state from oxidized to reduced (or maybe the other way around; absorbing a photon causes the pigment to bleach, or lose its color), thus turning the visual signal into an electrochemical one. The electrochemical signal eventually becomes a nerve impulse on the optic nerve that is transmitted to the brain, where the visual cortex interprets it as colored light. The different pigments respond to different degrees to photons of a particular wavelength (that is, the equilibrium between bleached/unbleached pigment molecules will be shifted to one side or the other to different degrees for different pigments). The relative degree of bleaching of each pigment is what determines which color will be seen. Suppose we have 3 pigments (A, B, C) and the degree of bleaching in yellow light (say, one of a single wavelength is A:20%, B:40%, C:80%. Now suppose that there's a red wavelength that produces the bleaching pattern A:18%, B:30%, C:10% and a green wavelength with the pattern A:2%, B:10%, C:70%. If you expose the pigments to both the red and green wavelengths at the same time, and you get the intensities right, you can get the bleaching pattern A:20%, B:40%, C:80%. The eye/brain will "see" yellow even though there isn't a yellow wavelength photon to be found. This is a crude example, but it illustrates the principle involved in mixing pigments to achieve colors. Dr. Land (of Polaroid fame) discovered that the choice of primary colors mixed to achieve the spectrum is fairly arbitrary--they don't have to be red-green-blue or the blue/yellow red/green complement pair. Likewise, the number of colors is arbitrary, although you need at least three for best effects. What is important is that the colors you choose bleach the various retinal pigments to sufficiently different degrees that the visual cortex interprets it as different colors. --PSW
msw1633@zeus.tamu.edu (WHITSITT, MARK STEVEN) (03/23/91)
In article <00945FE5.1F9B5480@aclcb.purdue.edu>, miguel@aclcb.purdue.edu (Phillip) writes... > > The additive primary hues, according to an undergrad general psychology >text book I have (Gleitmann (sp?)), are blue and yellow (which are >complementary) and red and green (complementary).... > The subtractive primaries are different. Two pigments mixed together >only allow wavelengths neither absorbs to be reflected. > So how does a color TV work? I understand that it uses only red green >and blue and that red and green mixed together (and surely this would be an >additive process, not a subtractive one) produce yellow. > Does anyone know? > _ _ >__________________________ _ (_) ________(_)________________________ >Phillip SanMiguel _/ \ / \ Purdue University Juggling Club As I understand it, the primary pigments (subtractive primaries), the primary hues of vision, and the primary colors of light are all different. The hues of vision are subject to stimulation of the rods and cones in the eye and then the brain perceives these as the various colors. Other than that, the pigments interact differently than the colors of light do to produce the various colors. It is all very involved and maybe someone can give a fuller explanation than this. Mark S. Whitsitt, N5RJF Texas A&M University, Dept of Biochemistry Bitnet: MSW1633@TAMSIGMA College Station, Tx. 77843-2128 Internet: MSW1633@SIGMA.TAMU.EDU (409) 845-0832 "You can't throw darts when you're empty, man" -- another Schadelism
jwtlai@watcgl.waterloo.edu (Jim W Lai) (03/23/91)
In article <4buhpE_00Vp54on145@andrew.cmu.edu> jpab+@andrew.cmu.edu (Josh N. Pritikin) writes: >miguel@aclcb.purdue.edu (Phillip) writes: >> The additive primary hues, according to an undergrad general psychology >> text book I have (Gleitmann (sp?)), are blue and yellow (which are >> etc... > >I suggest that you find a computer with a 24-bit color display and >play with a color painting program for a couple of hours. Also note >that color is just half the story, texture is very important in what >we think of as color. > >joshp -> t It has been found experimentally that three color stimuli (not four) are sufficient to produce color matches. This is why color monitors have three phosphors, not four. The empirical rules that describe this are known as Grassmann's Laws. Strictly speaking, texture is a property of surfaces (or virtual surfaces in this case), not color. It can affect color perception, yes.
todd@pinhead.pegasus.com (Todd Ogasawara) (03/24/91)
In article <00945FE5.1F9B5480@aclcb.purdue.edu> miguel@aclcb.purdue.edu (Phillip) writes: > The additive primary hues, according to an undergrad general psychology >text book I have (Gleitmann (sp?)), are blue and yellow (which are >complementary) and red and green (complementary). Blue, yellow and green >all have a "unique" wavelength at which the human eye/brain percieves them [...] >grey (i.e. blue + yellow = grey). The process is called "opponent-pair" or [...] > So how does a color TV work? I understand that it uses only red green >and blue and that red and green mixed together (and surely this would be an >additive process, not a subtractive one) produce yellow. I'm not familiar with the text you mention. However, I suspect you may have missed a few pages. The processing of color in human vision occurs at several levels. The level you mention (opponent pair stuff) occurs further down the processing chain. The processing of primary colors occurs at the retinal level (you might want to read Boynton's "Human Color Vision" to get the full biochemistry of this process) in sensory cells called the cones which fire optimally when absorbing wavelengths which we call red, green, and blue (RGB). There are also retinal cells called rods which play a primary role in night vision. Human color vision is, of course, much more complex than simply the two levels mentioned so far (retinal and bipolar cells). The Land effect certainly seems to indicate that their are higher cognitive factors that come into play. The perception of "brown" which appears to require a contrasting surround to occur is another indication of other higher processing. It has been years since I've looked at the literature though. So, if anyone else has more recent info to chime in with, I'd be interested to read it. -- Todd Ogasawara ::: Hawaii Medical Service Association Internet ::: todd@pinhead.pegasus.com Telephone ::: (808) 536-9162 ext. 7
vangeldr@cmgm.Stanford.EDU (Russ Van Gelder) (03/24/91)
A little more information on trichromacy. The original experiments which indicated that there are three photoreceptors came from experiments where subjects were asked to match any given hue with combinations of 2, 3, or 4 single colors; 3 turned out to be sufficient when the colors were red, green, and blue (RGB). Further work showed that color vision is mediated by the cones of the retina, which are concentrated in the region of highest visual acuity, the fovea. The surrounding areas are primarily populated by the more sensitive rods, which are used in night vision. This distribution explains why astronomers often peer at the stars using their peripheral vision; looking dead-on at a star dims its appearance because of the lower efficiency of capture and signal transduction of the cones in the fovea. The cone pigments themselves are fascinating. Like the rods' rhodopsin, the cone pigments are made up of a vitamin A-derived molecule, retinal, and a specific protein, opsin. There are three opsins, one for each color. One cone cell makes only one kind of opsin; how this level of differentiation is established is a great open question. Equally intriguing is understanding how the cone pigments "tune" the retinal; it is the same photoisomerization of 11-cis retinal to all trans which is the essential act of photoreception in all three cone rhodopsins. Something about the particular side-chains in the vicinity of the retinal must influence the absorption spectrum of the molecule; Jeremy Nathans (who worked out much of the molecular biology and genetics of human color vision) has been making site-directed mutants of the color opsins and thinks that the relative localization of charge on the retinal is responsible for its spectral absorbance. Higher order effects occur at the levels of center-surround interactions in bipolar and ganglion cells, and cortical processing; a number of optical illusions exists which show that the same spectral distribution is sensed as different color depending on its surround-field. No good algorithm yet exists for predicting how a particular spectral field will appear, which is to say that even the psychophysics of higher order visual perception are not yet well understood. Russ
msw1633@zeus.tamu.edu (WHITSITT, MARK STEVEN) (03/25/91)
In article <1991Mar24.002117.24100@medisg.Stanford.EDU>, vangeldr@cmgm.Stanford.EDU (Russ Van Gelder) writes... >.... Equally intriguing is understanding how the cone >pigments "tune" the retinal; it is the same photoisomerization of >11-cis retinal to all trans which is the essential act of >photoreception in all three cone rhodopsins. Something about the >particular side-chains in the vicinity of the retinal must influence >the absorption spectrum of the molecule; Jeremy Nathans (who worked >out much of the molecular biology and genetics of human color vision) >has been making site-directed mutants of the color opsins and thinks >that the relative localization of charge on the retinal is responsible >for its spectral absorbance. The idea that the opsin side chains "tune" the retinal then suggests many interesting variations on color perception. Consider an individual "A" having a mutation in one of his/her opsins which tunes the retinal differently than that of individual "B". Would placing A's eyes in B make B see colors differently than he/she did before? That is, would a familiar shade of, say, red, be perceived as a different shade of "red" with respect to the color individual B was accustomed to? What do ya think? Mark S. Whitsitt, N5RJF Texas A&M University, Dept of Biochemistry Bitnet: MSW1633@TAMSIGMA College Station, Tx. 77843-2128 Internet: MSW1633@SIGMA.TAMU.EDU (409) 845-0832 "You can't throw darts when you're empty, man" -- another Schadelism
chidsey@smoke.brl.mil (Irving Chidsey) (03/25/91)
In article <00945FE5.1F9B5480@aclcb.purdue.edu> miguel@aclcb.purdue.edu (Phillip) writes:
<
< The additive primary hues, according to an undergrad general psychology
<text book I have (Gleitmann (sp?)), are blue and yellow (which are
<complementary) and red and green (complementary). Blue, yellow and green
<all have a "unique" wavelength at which the human eye/brain percieves them
<to be without tinges of any other color. Red is "extra-spectral" in that
<it requires a combination of wavelengths to produce a "pure red"
<sensation. The complementary hues when mixed in equal amounts produce
<grey (i.e. blue + yellow = grey). The process is called "opponent-pair" or
<something similar. Mixing (adding) non-complementary hues produces an
<intermediate color (i.e. red + yellow = orange).
< The subtractive primaries are different. Two pigments mixed together
<only allow wavelengths neither absorbs to be reflected.
< So how does a color TV work? I understand that it uses only red green
<and blue and that red and green mixed together (and surely this would be an
<additive process, not a subtractive one) produce yellow.
< Does anyone know?
< _ _
<Phillip SanMiguel _/ \ / \ Purdue University Juggling Club
<miguel@aclcb.purdue.edu (_) \ / | *Juggling*Unicycling*COMBAT*
There is something called a C.C.I.E. diagram which plots all visible
hues. It is roughly, (very), triangular. If you plot the locations of any
three light sources on this diagram and connect them by straight lines they
will define a triangle. By varying the brightness of these sources, you can
produce light that appears to match any light source that maps to the inside
of the triangle. The light sources you can mimic depend on your initial
choice of your 'primary colors'. You can perform a similar excersize with
one white source and any three filters or pigments. The two sets of three
listed in the books are the optimum sets, but you don't have to use them.
You can do a little better if you don't restrict yourself to three.
I believe some high quality printers may use up to 8 or so, the final
decision is economic, which usualy means 3, because the additional sources
or filters don't add much. But 3 are essential.
The reason you can do all this is the human eye. It only has three
sets of color receptors, and their color ranges overlap.
Irv
Oh yes, your TV is color additive, usualy called RGB for red green
and blue.
--
I do not have signature authority. I am not authorized to sign anything.
I am not authorized to commit the BRL, the DA, the DOD, or the US Government
to anything, not even by implication. They do not tell me what their policy
is. They may not have one. Irving L. Chidsey <chidsey@brl.mil>news@linus.mitre.org (News Service) (03/25/91)
Your question about how a tv works is a little too open ended for me to be sure
what you are asking, but it is true that a color tv uses only red, green, and
blue. There are three "electron guns" that strike unique targets on a phosphor
film at the front of the crt. (If a gun strikes the wrong target, it will
produce the color of the target, so it is actually the film on the crt that
produces the light.
From: bkillam@ccels3 (bill killam)
Path: ccels3!bkillam
The human eye has cones for the same three primary additive colors (red, green,
and blue). This is based on some work in microspectrophotometry where single
cones in the eye were targeted by different wavelenghts of light and the
resultant reflcetion is measured (the differences in input/output determines
what input was absorbed.) An alternative hypothesis has been developed (as I
recall, primarily to explain the after image effect - "seeing" complimentary
colors when the stimulas is removed.) This hypothesis is called the opponent
process theory. This theory is based on observation (as far as I know). The
two theories have always been in conflict since neither can explain the findings
of the other.
Bill Killam
/---------------------------------------------------------------\
| Bill Killam | bkillam |
| MITRE Corporation | Phone: 703-883-7943 |
| 7525 Colshire Drive | FAX: 703-883-7934 |lfk@eastman1.mit.edu (Lee F. Kolakowski) (03/26/91)
On 25 Mar 91 06:38:12 GMT, msw1633@zeus.tamu.edu (WHITSITT, MARK STEVEN) said: > In article <1991Mar24.002117.24100@medisg.Stanford.EDU>, vangeldr@cmgm.Stanford.EDU (Russ Van Gelder) writes... >>the absorption spectrum of the molecule; Jeremy Nathans (who worked >>out much of the molecular biology and genetics of human color vision) >>has been making site-directed mutants of the color opsins and thinks >>that the relative localization of charge on the retinal is responsible >>for its spectral absorbance. Not just Jeremy Nathans, but several other labs as well. > The idea that the opsin side chains "tune" the retinal then suggests > many interesting variations on color perception. Consider an > individual "A" having a mutation in one of his/her opsins which > tunes the retinal differently than that of individual "B". Would > placing A's eyes in B make B see colors differently than he/she did > before? That is, would a familiar shade of, say, red, be perceived > as a different shade of "red" with respect to the color individual B > was accustomed to? What do ya think? This is true. There are individuals who are color blind who have a wide range of differences in their physcophysical perceptions. These are test by asking persons to adjust two knobs on a device which alters the ratio of red and green which make yellow, and comparing the color to "spectrally pure" yellow. THis test was devised by Lord Rayleigh. It turns out that some of these people have hybrid red/green photoreceptors. Also various mutations in rhodopsin can alter the wavelength at which it is most sensitive. -- Frank Kolakowski ======================================================================= |lfk@athena.mit.edu or lfk@eastman1.mit.edu or kolakowski@wccf.mit.edu| | Lee F. Kolakowski M.I.T. | | Dept of Chemistry Room 18-506 | | 77 Massachusetts Ave. Cambridge, MA 02139 | | AT&T: 1-617-253-1866 #include <disclaimer.h> | ======================================================================= ||Desert Storm - Lasers have made this the cleanest *dirty war* ever.|| =======================================================================
lstowell@pyrnova.pyramid.com (Lon Stowell) (03/26/91)
In article <91082.015922JMS111@psuvm.psu.edu> JMS111@psuvm.psu.edu (Jenni Sheehey) writes: > >This isn't my strong point, but I think I see where the confusion comes >from. Additive mixing refers to light. Subtractive mixing refers to >pigment/crayons/what have you. The additive primaries are red, blue, and >green, while the subtractive primaries are red, blue, and yellow. The additives are red, blue, and green. The subtractives are yellow, cyan, and magenta.
vangeldr@cmgm.Stanford.EDU (Russ Van Gelder) (03/26/91)
The suggestion that allelic polymorphism could lead to a "tetrachromacy" is interesting; however, it would take a novel mechanism to produce such a beast. The trichromacy system works because 1.) each cone only produces one of the three color pigments, and 2.) its connections are segregated by color; in fact, in the highest density region of the fovea, each cone synapses on only a single bipolar cell. First, men are not affected by such polymorphisms for the red and green loci, since they are X-linked. Although a given man may have up to four copies of the green (I think) gene in a tandem array, and although these may show variation, I don't think that this variation would be propagated to individual cones, and all cones expressing the same suite of genes would have the same spectral response. I don't think this would lead to the ability to detect new colors. In women, the story is more interesting. A woman can be heterozygous for the color pigments (which is why they rarely have red-green color blindness); but each individual cell inactivates one of the X chromosomes, making the retina a chimera of each of the genes. Thus, a woman could have functional segregation of four or more photoreceptors. However, in order for this information to be processed, the higher order neurons in the pathway would have to have a way to know *which* X was inactivated; perhaps this could be through some sort of an activity-dependent process. As for the blue pigment, which is autosomal, a mechanism to increase the number of photoreceptors would have to include allelic exclusion, such that only one allele of a heterozygote would be expressed. Although such a mechanism exists in the immune system, to my knowledge it is not utilized in any other autosomes. Russ
arromdee@cs.jhu.edu (Kenneth Arromdee) (04/14/91)
In article <15410001@hp-and.HP.COM> panek@hp-and.HP.COM (Jon Panek) writes: >... a more accurate nomenclature for the subtractive primaries are >magenta, cyan and yellow. >... >Folklore has it that the aforementioned Dr. Land would call up the >CEO of Crayola on an annual basis, slightly before Christmas. He >demanded that Crayola include in its crayon sets three crayons which >were accurate primaries. He claimed that children in elementary >schools were being misled when told that "mixing red and yellow >gives you orange", or "mixing blue and yellow give you green". Each >year the CEO replied that no, the subtractive primaries hadn't been >included. This is silly. As a kid I had Crayola crayons that most definitely _did_ include at least magenta, and after learning about subtractive primaries I tested it myself by combining magenta and yellow, and sure enough it _did_ give red. Yellow and purple also gave a nice brown. [Note the followup-to line.] -- "If God can do anything, can he float a loan even he can't repay?" --Blair Houghton, cross-posting Kenneth Arromdee (UUCP: ....!jhunix!arromdee; BITNET: arromdee@jhuvm; INTERNET: arromdee@cs.jhu.edu)
winalski@psw.enet.dec.com (Paul S. Winalski) (04/14/91)
In article <15410001@hp-and.HP.COM>, panek@hp-and.HP.COM (Jon Panek) writes: |>During all this talk about additive and subtractive color primaries, |>people have been overlooking a subtle but important point. While it |>is true (I believe) that the additive primaries are red, green and |>blue, a more accurate nomenclature for the subtractive primaries are |>magenta, cyan and yellow. |> |>Folklore has it that the aforementioned Dr. Land would call up the |>CEO of Crayola on an annual basis, slightly before Christmas. He |>demanded that Crayola include in its crayon sets three crayons which |>were accurate primaries. He claimed that children in elementary |>schools were being misled when told that "mixing red and yellow |>gives you orange", or "mixing blue and yellow give you green". Each |>year the CEO replied that no, the subtractive primaries hadn't been |>included. Perhaps Dr. Land had stricter definitions for "green" and "orange" than the layman's use of those color terms. Anyway, mixing red and yellow crayola colors, poster paints, or inks *does* yield a mixture whose color is a shade of orange, and mixing blue and yellow *does* give you a shade of green. This is trivially verifiable by experimentation. --PSW