From: kps@cunixb.cc.columbia.edu (Karthik P Sheka)
Newsgroups: alt.folklore.computers,rec.games.int-fiction
Subject: Re: Screen colors (Was Re: Zork/Dungeon)
Date: 10 Oct 92 03:12:06 GMT
Reply-To: kps@cunixb.cc.columbia.edu (Karthik P Sheka)
Organization: Columbia University

In article <rdippold.718652903@qualcom> rdippold@qualcom.qualcomm.com (Ron Dippold) writes:
>david@datamark.co.nz (David Rowland) writes:
>>4 Million Now. A few messages back, it was 350 000 colours. Does any
>>one know the exact number of colours the human eye can see?
>
>It depends on the medium.  I know that for many printed colors, you can
>take a background of some 24-bit color value, then impose a shape on
>it in which the color varies only in the lsb of one of the RGB
>components, and people can observe the shape.  For monitors, however,
>there is less discrimination.  I would tend to doubt the 350,000
>colors, since the 256,000 available for VGA are so easily
>distinguishable from each other.

This is one of those times I wish I hadn't cut my Computer Graphics' class
on color.  This is what I understand about it, though, from argueing with
the teacher and T.A. (With a little biology thrown in):

The human eye picks up only three colors, in different receptors (cones?):
red, green, and blue.  All shading is done by the ratio of the receptors
with each other.  There is a slightly larger amount of one of these types
of receptors than the other two. (I can't recall which one, but I think it
was green.)

When a computer creates a color image (usually) it does so by assigning a
certain number of bits to each of the primary colors. (again, red, green,
and blue.)  VGA comes in 4 and 8 bit flavors, (2^4 == 16, 2^8 == 256) , so
the number of colors seen in VGA is either 16 or 256.  Actually, VGA uses 8
bits, but I believe that they swap between two sets of four bits each, or
something, due to limitations on the memory throughput. (Add more memory to
a 16 color VGA card will usually give you a 256 color VGA card.)

Some of the nicer "super" VGA cards use 16 bits for color, giving 65536
colors.  Since 2^16 cannot evenly be distributed among the three primary
colors, the extra bit is usually given to the primary that we can see more
shades of. (2^6 greens, 2^5 reds, 2^5 blues).

Most graphics workstations now come with 24 bit color.  This gives 8 bits
of color for each of the primaries, or about 16 million colors.  Some of
the more powerful graphics workstations now, and the graphics mainframes
and such come with 48 bit color, giving two bytes of color information to
each of the three primaries (giving 281 trillion colors).

We've already passed the point of diminishing returns, however.  The most
significant difference is between 16 and 256 colors for most computer
applications.  For image-processing, 16 bit color is usually enough, with
24 bit color used for serious tv-like color.

As for how many colors a person can see, its not a constant even for a
single person in a single one-hour period.  If the colors being viewed are
very similar, say shades of green, the eye can pick up more colors within
those shades.  This is because the cones in the eyes that pick up that
color get "tired", and the cones of the other colors have an easier time on
picking out the information that they can read.


No matter how many colors a flat computer display can have, however, it
will never be realistic enough to seem three-d. (I'm not counting stuff you
can do with polarized glasses or other pheriferals.)  This is because, for
an object to seem three-d, it has to direct the light at a lot of different
angles, which is not possible on a flat screen.


This article turned out a lot longer than I initially expected.  I guess
the moral is that you probably don't need a 24 bit video card, and to
invest in holographic displays.

//Karthik