[Coco] Documentation of "complex" artifacting (i.e. more than black/white/blue/red)?

[John W. Linville]

On Sat, Sep 25, 2010 at 11:28:14PM -0400, Robert Gault wrote:
> John W. Linville wrote:
> 
> >Thanks, Robert.  But while that helps explain the 01 and 10 patterns
> >(which fit into the time slot for a single NTSC color pixel), I don't
> >think it addresses the patterns involving more than two bits.
> >
> 
> Sure it does. Think of the screen as having a certain number of
> pixels per color burst cycle. The average location of the pixel
> pattern within a color burst is the fake phase angle. In addition,
> there is a blend of artifact colors depending on which colors are
> side-by-side.

Yes, but the 256-pixel wide mode (along w/ the border) allows for
exactly two b&w pixels per color burst cycle [1], not 4, 8, or whatever.
That only allows for two fake phase angles (or no phase shift at all)
and therefore only accounts for two artifact colors.  Also it doesn't
account for the use of alternating patterns on different horizontal
lines, which are reasonably far apart temporally even if they are
physically adjacent.

Blending colors side-by-side seems like a more reasonable possibility
to explain the "complex" artifacting.  It may account for the
multi-line artifact patterns as well.  A "phosphor overglow" (or
whatever) explanation for the phenomenon may account for why the
"complex" artifacts don't seem to occur on LCDs or even some modern
CRTs.

> It is trivial to place on a graphics screen a repeating bit pattern
> to see what color is generated. You can even write a Basic program
> to do that.

That may prove the "what", but it doesn't explain the "why".  Anyway,
as I have stated elsewhere the "complex" artifacting programs don't
seem to produce any of these extra colors on any of the more modern
displays I've used (such as LCDs or my 90's-era TV).

John

[1]  If they weren't thusly aligned, then a "01" would produce
different colors at different points along the horizontal.
-- 
John W. Linville                Someday the world will need a hero, and you
linville at tuxdriver.com                  might be all we have.  Be ready.