Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!tektronix!gvgpsa!gvgspd!mrk
From: mrk@gvgspd.GVG.TEK.COM (Michael R. Kesti)
Newsgroups: comp.sys.ibm.pc
Subject: Visual perception (was Re: Photographing PC Screens)
Message-ID: <698@gvgspd.GVG.TEK.COM>
Date: 23 Mar 89 01:23:39 GMT
References: <3779@peora.ccur.com> <3939@kuhub.cc.ukans.edu> <7454@pyr.gatech.EDU> <17769@onfcanim.UUCP> <29050@sgi.SGI.COM>
Reply-To: mrk@gvgspd.GVG.TEK.COM (Michael R. Kesti)
Distribution: na
Organization: The Grass Valley Group, Grass Valley, CA
Lines: 35

In article <29050@sgi.SGI.COM> donl@glass.SGI.COM (donl mathis) writes:
>When i get two feet away from my monitor, it sure doesn't *seem* to be
>four times as dim as when i'm one foot away!  And when i'm several
>miles from Halfdome, it sure doesn't seem any dimmer than when i'm
>right at the base.  And a light bulb doesn't seem to get any dimmer
>when i back away from it.

The keyword here is "seem".  My camera and monitor setup and maintenance
experience with my previous employer (WNMU-TV, Marquette, Mi.) taught me
some very surprising lessons concerning our perception of light and color.
The human eye (and its attendant processor, the brain), is very capable of
"correcting" the observed scene in order to make things make sense.  For
example, if one color balances a camera under incandescent light, and shoots
a scene containing a white object, that object will appear white both on the
monitor and to the eye.  If one then substitutes flourescent lighting,
without rebalancing the camera, that white object will still appear white
to the eye, but on the monitor it becomes decidedly blue.  What happens is
that our brain knows the object is white, and therefore corrects the scene
to allow you to percieve it "correctly".  The camera and monitor have no
such ability, and therefore display the reality of the situation.

A similiar phenomenon occurs in the examples cited above, within limits.
Take backing away from the light bulb, for example.  Take this to extremes
(say back off from one foot to one mile) and of course the apparant
brightness changes.  Under smaller limits, however, the eye/brain combo
does its best to provide useful and sensible data.

I realize this only slightly relates to the discussion at hand, but I
couldn't resist expounding on a subject I find fascinating and about which
I know something! :-)
-- 
============================================================================
Michael Kesti  Grass Valley Group, Inc. | "Like one and one don't make two,
    @gvgspd.GVG.TEK.COM                 |  one and one make one."
    !tektronix!gvgpsa!gvgspd!mrk        |         - The Who, Bargain