Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!nrl-cmf!ukma!husc6!bu-cs!buengc!bph
From: bph@buengc.BU.EDU (Blair P. Houghton)
Newsgroups: comp.cog-eng
Subject: Re: Color in Screen Displays
Message-ID: <1668@buengc.BU.EDU>
Date: 13 Dec 88 20:05:16 GMT
References: <2789@hound.UUCP> <1724@hp-sdd.HP.COM> <234@lynpac.oz>
Reply-To: bph@buengc.bu.edu (Blair P. Houghton)
Followup-To: comp.cog-eng
Organization: Boston Univ. Col. of Eng.
Lines: 32

In article <234@lynpac.oz> croot@lynpac.oz (0000-Admin) writes:
>In article <1724@hp-sdd.HP.COM> andrea@hp-sdd.UUCP (Andrea K. Frankel) writes:
>>In article <2789@hound.UUCP> nib@hound.UUCP (N.BENIMOFF) writes:
>
>From some work long ago, all I CAN remember is that you should never use
>red-on-blue or vice-versa (eg. red text on blue background). Apparently
>the eye adjusts its focus slightly for some colours, red and blue being
>the worst two (This sounds like crap - and probably is - but the original
>assertion is true), therefore the eye *cannot* focus properly since one of
>the red/blue foreground/background will be slightly out of focus. I know
>that on my terminal, I find it very hard to read. Matt.

It's physics, and due to the achromaticity of the lens.  Red and blue,
being at opposite ends of the spectrum (ROYGBIV and all that) refract
to very different angles in the eye.

This explains the fact that they are focussed differently.  I say this
because many such things (e.g. misdetermination of intensity due to
differences in contrasting surroundings) are a result of retinal processing
and Higher Neural Function.  This one just happens to have a purely
physical basis.  (I'd expect that the visual system was capable
of eliminating the problem through some sort of processing, but it
doesn't.)

The really interesting thing is that they appear (it's a Famous Optical
Illusion) to be at different distances from the eye, when clearly they
are not, considering that it is very difficult to determine distance
from focus alone, and parallax is nonexistent if the two colors are in
the same plane.  Perhaps that slight misfocus is perceived as a separate
object.  Perhaps not.  It's easy to get fooled by these things.

				--Blair
				  "White on DarkOliveGreen."