Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!uunet!portal!cup.portal.com!Sullivan
From: Sullivan@cup.portal.com (sullivan - segall)
Newsgroups: comp.sys.amiga
Subject: Re: How do you turn on flicker?
Message-ID: <17700@cup.portal.com>
Date: 28 Apr 89 05:56:11 GMT
References: <1076@altos86.UUCP>
Distribution: usa
Organization: The Portal System (TM)
Lines: 44

>I recently received an Amiga 2000 with a NEC Multisync II monitor
>with the intention that I would put up with this flicker thing
>until the "?new chips?" come out.
>
>Chuck L. Peterson
> ...!sun.com!altos86!clp

Flicker is caused by the 30 frame per second update rate.  The phosphor
in most CRTs is optimized for 1/60th of a second per page.  In interlace
mode the first screen is updated in 1/60th, and the second is updated 
during the next 1/60th.  The first is composed of all of the even scan
lines, and the second is composed of the odd ones.  Since the phosphor
has already died from the first screen by the time the second is being
shown, any bright points which neigbour dark ones vertically on the screen
will seem to disappear and reappear twice every 1/30th.  
 
The reason for this effect is complex.  Although 1/30th of a second should
be above the flicker rate for human visual perception, (movies typically)
run at 24 frames per second.) it is noticeable when compared to other
lines which are not flickering.  These other lines are the interlaced 
lines.  One effect that interlacing has on human visual perception is that
the slight upward/downward motion of the alternating lines is resolved 
automatically into a single line.  Thus the perceived resolution is half
of the actual resolution for an interlaced screen.  And as a net result,
successive lines which are light and dark seem to flicker.  

To experience this on your multisynch monitor, select the preferences
icon, choose some contrasty colors, and turn on the interlace.  After
saving your configuration reboot and you'll see your screen come to 
life.

 
                           -Sullivan Segall
_____________________________________________________________
 
/V\  Sully set the example: to fly without moving.  We shall
 '   learn to soar on wings of thought. And the student will
     surpass the teacher.
To Quote the immortal Socrates: "I drank what?" -Sullivan
_____________________________________________________________
 
Mail to: ...sun!portal!cup.portal.com!Sullivan or
         Sullivan@cup.portal.com
 )