Re: [stella] How many NTSC colors?

Subject: Re: [stella] How many NTSC colors?
From: "Eric Ball" <ericball@xxxxxxxxxxxx>
Date: Thu, 14 Jul 2005 07:23:51 -0400
From: "Chris Wilkson"

> It is possible to make the delay too large, so that the phase delay
> for color 15 is equal to or more than 360 degrees.  When the delay
> equals 360 degrees, the effect is that color 15 = color 1 = gold.
> But there will be a 1 pixel delay to the right for color 15.  If the
> phase is > 360 then color 15 could be equal to color 2, 3, etc...

Umm, why would there be a delay?  Inside the TIA the colors are simply taps
along a delay line which the colorburst signal travels down.  This is a
continuous process so at any instant color 1 = phase p, color 2 = phase p +
d, color 3 = phase p + 2d, etc.  So if d = 24 degrees then the phase of
color 1 and color 15 will match.

Each pixel a tap is turned on for 280ns, which happens to be one complete
cycle of colorburst (well, except for color=0, in which case the color is
supressed); so from phase p to phase p + 360 degrees.  During that same
280ns the luma DAC outputs one of 8 levels.  The luma and color signals are
combined and sent to the TV.

The TV uses a filter (lowpass, notch or comb) to separate the luma and color
signals, demodulates the color signal to extract the in phase and quadrature
components (the phase), and runs the three YIQ inputs through a matrix to
produce RGB outputs which are then sent to the guns.  Whee!

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