Re: Double hires mode color artifacts

["Michael J. Mahon" <mjmahon@aol.com>]

vladitx wrote:
> On Sep 11, 10:28 pm, Dirk Thierbach <dthierb...@usenet.arcornews.de>
> wrote:
>
> > Dirk Thierbach <dthierb...@usenet.arcornews.de> wrote:
> >
> > > Linards Ticmanis <ticma...@gmx.de> wrote:
> > >
> > > > Here's a RGB color table that works well enough for this (derived from
> > > > Fourier Analysis and the usual YUV-to-RGB formulas):
> >
> > > > static struct {
> > > >       unsigned short  red;
> > > >       unsigned short  green;
> > > >       unsigned short  blue;
> > > > } AppleIIColor[16]= {
> > >
> > > [...]
> > >
> > > >       {0x40,0x54,0x00},       /* Brown */
> > > > };
> >
> > > While testing double hires, I noticed that this color comes out on
> > > my monitor as some sort of olive green, and not brown. What's wrong?
> >
> > I've tried to do the Fourier projection myself, but I arrive at different
> > values. Do you assume any phase shift between the square waves of the
> > bit pattern and the sine/cosine base functions?
> >
> > - Dirk
>
>
> I suppose there's phase shift between the colour reference mixed into
> the NTSC signal and the video data. They come from the same master
> clock, but pass through different gates. Can somebody measure this on
> a real Apple?
> Any angle like this should be taken into account.

And there's an LC tank circuit for adjusting the burst phase, as Linards
noted.

-michael

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