[Coco] 384 or 450 scanlines ?

[John Kowalski]

Art Flexser wrote:
>I guess what's puzzling me is this: as I now understand it, every
>frame is ordinarily repeated twice in succession identically, with the
>second repetition landing smack on top of the first, with a frame
>occurring every 60th of a second and using only every other scan line.
>Wouldn't it have looked better if the second repetition was one scan
>line offset from the first instead of on top of it? Would the 6947Y
>VDG accomplish that?

It's not so much that every frame is repeated twice, they are all full
frames; updating at 60 times per second - just at a lower perceived
resolution than broadcast NTSC standard.

But yes, I think the 6847Y would have been a drop-in replacement.
I've never seen one in the wild so I suspect maybe they didn't sell
very well.

And yes, that chip would have offset even/odd frames vertically so
there would be no visible black lines between scan lines.   Visually,
it would have made the low resolution of the graphics look blockier
and the interlacing would have caused a minor visible jitter.  Not
sure if you could call that better than the *solid* 256x192 a CoCo 1/2
normally generates, except that it would have opened a door for
programmers to exploit a potential 256x384 resolution if a program
carefully alternated between two different images.

-- 
John Kowalski / Sock Master
http://users.aei.ca/twilight/sock