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

[gene heskett]

On Sunday, September 26, 2010 07:19:35 am john dumas did opine:

>   On 9/25/2010 11:21 PM, John W. Linville wrote:
> > 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.
> 
> Remember that alternate lines are actually alternate _screens_ due to
> interlace. Each screen is 1/2 horiz line off from the previous one and
> the VDG would start it on the opposite phase of it's clock. The same
> clock that is the color burst.............
> 
> cheers,
> johnd
> 
While technically true for a fully NTSC system, the coco is not such a 
beast, so the 1/2 cycle color subcarrier offset on alternate fields does not 
exist in the coco world.  In any of its video chipsets.
> 
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