Re: 560 out of 563 Pixel Per Line?

[pausch@saaf.se (Paul Schlyter)]

In article <TrEEe.2367$Ok6.1191@newssvr29.news.prodigy.net>,
Bryan Parkoff <nospam@nospam.com> wrote:
 
>     I know the fact is that Apple II is designed to position one out of 16 
> colors from position 0 through position 559 which it shows 560 x 192 
> resolution.  It seems to be strange that NTSC paints one out of 16 colors 
> from position 0 through position 562 which it shows 563 x 192 resolution. 
> It seems to be extra 3 pixels in the right farther from position 559.  If 
> you turn on monochrone, it will only show 560 x 192 resolution instead of 
> 563 x 192 resolution.
>     If you use RGB monitor, it always shows 560 x 192 resolution.  How can 
> you please explain why it is the way how NTSC uses extra 3 pixels?
 
NTSC is an analogue, not digital, TV system.  Therefore NTSC itself
does not use pixels.  NTSC does have an upper limit for its video
signal though, and individual variations in this upper limit (and of
other video parameters) between individual TV sets can easily become
larger than 560 compared to 563.
 
The Apple II uses pixels, and converts them to an NTSC video signal.
The designers of the Apple II of course wanted it to work with as
many TV sets as possible, therefore they avoided squeezing as many
pixels as possible into one line but instead settled for a more
reasonable number of pixels.  Therefore some TV sets can appear to
have room for 3 "extra" pixels while others may appear to have room
for, say, 10 "extra" pixels.
 
>     In Low Resolution -- If you use "color=1 : plot 0,0" and "color=2 : plot 
> 0,1", do you notice that dark blue color does not paint in position 0?  If 
> you use "color=4 : plot 0,3" and "color=8 : plot 0,4", do you notice that 
> dark green color does not paint in position 0 and position 1 and brown color 
> does not paint in position 0 through position 2?  Can you please explain why 
> NTSC does not paint while it always leave positions blacker or no color?  It 
> is likely that NTSC can only show 3.5 pixels per one video cycle.  It can 
> mean four dots (4 bits) equals to one pixel).  How can RGB monitor display 
> 14 pixels per one video cycle?  I assume that RGB monitor does not use 3.58 
> MHz.
> 
>     It is interesting.  Please comment and ask why.
 
The RGB monitor most likely has a much larger video bandwidth than an NTSC
TV.  Therefore the video monitor is able to display more pixels per
"video cycle" (whatever that is.... :-)
 
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