[Coco] 384 or 450 scanlines ?

[Arthur Flexser]

Thanks, John.  A look via eBay and Google turned up zero sources for
the 6847Y, so I guess your assessment of how it would have looked in a
CoCo probably won't ever be verified by actual experience, unless
there's somebody out there that tried one way back when out of
curiosity.

Art

On Mon, Jan 13, 2014 at 2:51 PM, John Kowalski <sockmaster at gmail.com> wrote:
> 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
>
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