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

[john dumas]

  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