sims@hou2b.UUCP (12/10/83)
I have noticed a similar effect when I was a graduate student
at the U. of Illinois. After several hours working on an
orange/red plasma PLATO terminal, all whites (particularly
chalk lines on a blackboard) were shifted to blue.
--
Jim
houxm!hou2b!simslat@wbux5.UUCP (12/11/83)
I have noticed the same...I am currently using a Concept AVT terminal, black background w/orange letters (can use it in reverse also), and I am also seeing blue writing on the chalkboard, instead of white.....I don't remember having a problem like that with my HP2621...I also notice that in the course of the day my eyes are more tired than they usually are...could this be caused by the Concept? I had heard that amber on black was much easier on the eyes...is orange on black as bad as white (or green, whatever the HP was) on black? Laurie [ihnp4, houxf]wbux5!lat
rfg@hound.UUCP (R.GRANTGES) (12/12/83)
About three centuries ago when I was in school, one of the things they told you about in introductory Psych was a phenomena (I've forgotten its name) wherein the eye behaves very much as you all have been describing. It can be demonstrated easily by gazing fixedly at any strongly colored surface, then looking away at some neutral (grey, white) surface. You will see the second surface not as grey or white but as the complementary color of the first surface. Don't know why, but that's how it works. Effect is well known, don't worry about it - that's my message. -Dick Grantges HO hound!rfg
judd@umcp-cs.UUCP (12/12/83)
.......
Colors of phosphors can be ranked from best to worst thus:
amber (a very specific color), yellow, green, orange, red, blue
This ranking comes from various research done in Europe. The papers
can be found in a book whose title I have forgotten. I found it searching
through the card catalog for books on human factors research.
Note that some greens are much worse than others. The papers quote specific
phosphors. The P3 used by the IBM monochrome monitor is good. Whatever
is used by techtronix 4025 is pretty poor.
--
Spoken: Judd Rogers
Arpa: judd.umcp-cs@CSNet-relay
Uucp:...{allegra,seismo}!umcp-cs!juddlwr@ih1ap.UUCP (L. W. Retzner) (12/12/83)
I have noticed the same phenomenon when wearing rose colored ski goggles on a bright sun suny day. When ever I took the goggles off the snow would turn green for a few seconds. It did not take too long for my eyes to readjust or to put the goggles back on because of brightness. Bill Retzner ihnp4!ih1ap!lwr
walsh@ihuxi.UUCP (12/13/83)
Your eyes will always 'see' the complimentary color of anything you've been looking at for a while, when you look at a white or pale surface. Such as when you stare at a blue (bright) image for a few seconds, and then look at the white cieling, you'll see an orange 'shadow' that is the same shape as the blue image. Green and red are complimentary, and the image is pink because of the brightness and light value of the green on terminal screens. I have a green on black screen, and I'm always seeing pink! I don't know the exact medical reasons for this reverse imaging; maybe the cones in the retina have to compensate with a negative image. When I had a blue on black screen, I never noticed this (i.e., I didn't see orange), but I think that's becasuse the blue used is more like a grey, while green screens are REALLY green. B. Walsh
zben@umcp-cs.UUCP (12/13/83)
Last time I looked the theory was that there are three different pigments in the cones (color-vision cells) of the eye. I suspect one of the pigments or it's associated neural net elements become fatigued, so that when you switch to a white or neutral stimulation the output is not quite balanced, and a perception of a pale color results... Ben Cranston ...seismo!umcp-cs!zben zben@umd2.ARPA
daemon@decwrl.UUCP (12/14/83)
From: Joe Falcone HLO2-3/C09 dtn: 225-6059 <erlang::falcone> CC: I don't claim to be an expert on the matter, but a a year ago I spent a few months studying color vision (in particular, the perception of color vs. black-and-white images on computer displays), and the one thing that amazed me about the field was how little we know for certain about the mechanisms of color vision. There are many theories, but very little evidence (since that would involve possibly destructive experiments). The following is a capsule of some theories. The theory proposed by Rick Wise is off the mark to begin with. The human eye does not work like a TV camera - and in fact few eyes in nature do. Instead of red, yellow, blue and intensity receptors, the eye has red and green receptors for bright light, intensity receptors for dim light, and there is some debate as to whether we have blue receptors at all (there are some visual tricks which can be explained by that). Hence, a workable theory (and one that I believe has been supported by some laboratory tests) is that under strong influence, a receptor can be suppressed, so that when the stimulus is removed, the other (or opponent) receptor begins showing a response that is greater relative to the other one. SO the green receptors are suppressed, and when the stimulus is removed, they shut off MUCH MORE than the red receptors do (since they are "exhausted" from the stimulus), so that the red receptors are providing relatively more input than the green receptors. Voila - Pink Walls! If anyone out there has a red phosphor terminal, I'd be interested in knowing whether the walls appear green after extended use. Notice also that this explains why users of blue phosphor terminals don't see orange or red/green walls - blue receptors are not that important to color vision and blue tends to stimulate/suppress red and green receptors equally. Joe Falcone decvax!decwrl!rhea!erlang!falcone DEC Research, Hudson, MA
msimpson@bbncca.ARPA (Mike Simpson) (12/14/83)
**
Somewhere in the misty eons of my memory, I remember
seeing an optical illusion somewhat similar to this. There
was a picture of an American flag, with black stars on a
yellow field, and green and black stripes. One was supposed
to look at this for about a minute, then quickly look at a
white wall. Voila -- a regular (red-white-blue) American
flag! The explaination (again, I'm relying on memory) was
that the cones in the back of the retina get tired when you
look at the same color for a period of time, and so the colors
get 'selected' out.
Flames to me, comments to the net.
Mike Simpson
msimpson@bbn-unix (ARPA)
{decvax,linus,wjh12}!bbncca!msimpson (Usenet)
--
-- cheers,
Mike Simpson
Bolt Beranek and Newman Inc.
Ten Moulton Street,
Cambridge, MA 02238 (USnail)
msimpson@bbn-unix (ARPA)
decvax!bbncca!msimpson (Usenet)
msimpson.bbn-unix@udel-relay (CSNET)
617-497-2819 (Ma Bell)seifert@ihuxl.UUCP (D.A. Seifert) (12/16/83)
I saw the same reverse US flag. It was in the World Book encyclopedia. It worked too. Snoopy -- ) ( ) from the mildly opinionated keyboard of _)__________________ |OOOOOOOOOOOOOOOOOO| Dave Seifert |OOOOOOOOOOOOOOOOOO| ihnp4!ihuxl!seifert |OOOOOOOOOOOOOOOOOO| |------------------|
eds@bunker.UUCP (Eric Schlesinger) (12/19/83)
Not so long ago, the BBC (that's in England, folks) did a series of Open University programs on such phenomena. It seems that it relates primarily to the organization of color receptors in the human eye, and the fact that when stressed excessively they fatigue rather rapidly. This is the case when one stares at a typical green phosphor for unduely long amounts of time. Afterwards, the other receptors are out of balance (in terms of strength of reception). So the brain receives an image which is more heavily excited to the other colors; since it appears that there are primarily red/green receptors, the green-induced fatigue produces a reddish aftereffect. (Note that most color-blindness is oriented towards red/green, and that part of a standard eye examination - the ones I've had, anyway - uses red and green filters to compare visual acuity.) I'm sure there's more and more detailed information regarding this sort of thing somewhere. But the above was picked up on a half-hour Open University show; of course, no one has ruled out that after staring at a CRT for hours one also has the tendency to drink excessively which can *also* account for everything having a reddish tinge. Eric Schlesinger Bunker Ramo Information Systems (known to the trade as BRIS)
eager@amd70.UUCP (01/03/84)
The eye adapts to the predominant color, trying to adjust to a neutral color balance. This is why colors seem constant when seen under daylight (at 6000 degrees Kelvin), tungsten light (2500 degrees) or candle (1000 degrees). That the reflected light is not the same color can be seen when you take a picture indoors with film balanced for daylight, or when the light in a room is a mixture of daylight and tungsten light. When you over-load the eyes with one color, it over-compensates with the opposite color. When you look away, the compensation remains for a time. If you look at a sheet of red paper for 30 seconds, and then look at something white, you will get an image of the complement, green. Similarly, with blue and yellow. If you look at a pattern of green squares separated by white borders, after a short time the borders will tend to look pink, especially at the corners.