Re: Apple ][gs VGA Card

[ntt@cleese.apana.org.au (Jonathan Pratt)]

blakjak@panix.com (Noah Mittman) writes:
> : I see what you are saying, but I can't understand how we perceive it as
> : higher resolution. Perhaps it's just an optical illusion.
> 
> It's the phenomenon we call persistance of vision. The best way of
> describing it the fact that if you had a light source that cut off
> instantly, your perception of that light would be a very quick fade to
> darkness. You simply can't perceive such a rapid change. So imagine that
> your monitor is a really elaborate strobe light which is flashing between
> odd lines and even lines before you can see them fade away.

No, this is incorrect.  There is physically 400 scan lines (or the room on
the screen where scan lines are drawn) drawn for each picture update.  But
only alternate ones are drawn each cycle, so that two cycles are required
to completely redraw the entire screen.  The phosphor on the screen holds
enough of the image for it to be seemn without too much flicker, but there
is little or no overlap of the two sets of images (they interlace each
other - hence the name)

cheers
ntt@cleese