Re: VGA to Monitor GS (Was Re: Apple IIGS on a VGA monitor...the hard way?)

[Joseph Lee <nuNOUBEgundam@netNOUBEcom.hotmail.com>]

Dave Althoff (dalloff@freenet.columbus.oh.us) writes:
<snip>
>Of course, one of the problems is that computers don't do the timing
>necessary for interlacing very well.  Interlaced displays tend to flicker
>because the signals don't line up exactly, so most computers use
>non-interlaced displays...both fields are identical.  I don't know if XGA

Actually no.  Flicker is a subjective thing dependant on sight and the human
brain.  ALL displays flicker; just below 70hz, it's more visible to most
human equipped sight systems.

Reason interlaced flickers more than none is that each field is on the screen
for 1/30 of a second.  This isn't too short a time.  However, when you're
swapping between 2 slightly dissimilar pictures in 1/30 of a second.  It's
just slow enough for the visual cortex to perceive that something was there
before it shifted.  Non-interlaced displays at below 70hz will also seem to
flicker.  Look at PAL.  It's 1/50 of a second refreshes (1/25 per field) and
it's fine to the rest of the world to watch with.

Why is 70hz somewhat a key scan-rate?  It's quite arbitrary, just that screen
redraws are fast enough that the eye doesn't preceive than blanking part of
the redraw through persistence of the image shifting fast enough.  The human
eye does not operate on a 60 fps cycle, just some arbitrary number that has
not really been quantitively measured.

Cheers,
-- 
Joseph nugundam =netcom=com/==\=IIGS=/==\=Playstation=/==\=Civic HX CVT=/==\
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