From: thornley@mega.cs.umn.edu (David H. Thornley)
Newsgroups: alt.folklore.computers,rec.games.int-fiction
Subject: Re: Screen colors (Was Re: Zork/Dungeon)
Date: 13 Oct 92 20:45:24 GMT
Article-I.D.: news2.1992Oct13.204524.21453
Organization: University of Minnesota, Minneapolis, CSci dept.

In article <o4yDsB1w164w@lorc.UUCP> lowen@lorc.UUCP (Lamar Owen) writes:
>xeno@iastate.edu (Gary L Snethen) writes:
>> In <Xs76RB1w164w@lorc.UUCP> lowen@lorc.UUCP (Lamar Owen) writes:
>> >xeno@iastate.edu (Gary L Snethen) writes:
>> [various discussions on how many colors you can see.]
>
>Also an interesting observation.  The eye, due to its dual nature, is very 
>sensitive to intensity variations in the GREY realm.  Why? Due to the splitting
>of the retina into cones and rods.  If I am not mistaken, cones perceive hue
>mostly, and rods perceive intensity.  Now, for survival, it is important to
>be able to distinguish an object even in low light levels.  This either implies
>a logarithmic scaling of intensity, or a generally better resolution of
>intensity.  Note that, at low light levels, everything is grey.  Very little
>color, since the cones don't do as well in low light.
>
I took a class in human vision last year, so I think I know what I'm
talking about.  Cones are used for detail vision in color at medium to
high light levels; rods are used for undetailed vision in black-and-white
at low light levels.  If you can easily see colors, your rods probably
aren't contributing much to your vision.  What you see as gray at higher
light levels is basically information from cones.

>In fact, the eye is more sensitive to some color frequencies than others.  I
>do not remember exactly which right at this moment, but the very act of
>color combining in a TV set makes use of this property to get the best
>possible perceived chroma resolution.  Acckk!  I wish I could remember my
>chroma bandpass filter gain ratios!  (NTSC, of course.  PAL uses a different
>ratio set because of the different modulation technique).
>
Cone cells come in three varieties, sometimes called red, green, and blue,
but the red and green are actually pretty close to each other in the
general area of orange and yellow, and they aren't real fussy about what
frequencies they'll detect.  Rods work best in greenish-blue, and so red
things look particularly dark at night.  Effectively, the cones can be
fooled by any three colors into seeing almost any possible color, although
some combinations are more efficient than others.  RBG is a good choice;
although it obviously cannot match any possible spectrum, it can simulate
the effects very well for the human visual system, since the eye can only
sample three frequencies (two in cats, four in bees, it varies among
species).  Of course, beings with different visual systems will not see
video screens, paintings, etc., in a different way.

We covered the number of possible colors only briefly, and I don't remember
it.  One interesting point is that the eye can differentiate far more
colors than it can recognize; i.e., two shades might look the same when
viewed separately, but might be easily distinguishable when together.

DHT

ObIntFict:  I had real problems playing Deadline because the rooms were so
undetailed.  A room would have a bed, a table, and a chair, each totally
without components.  I realize that this means that searching rooms in
detail is not productive, but it ruined the image for me.
Xref: sparky alt.folklore.computers:15089 comp.unix.admin:5591