Re: [stella] How many NTSC colors?

 Subject: Re: [stella] How many NTSC colors? From: Chris Wilkson Date: Thu, 14 Jul 2005 12:53:48 -0400
```You've sort of answered your own question, with a slight error.  If you
have colors 1-15, there are only 14 gaps between them.  So a properly
adjusted machine with d=24 degrees gives a total of 336 degrees...no overlap.

Now the answer to the delay question.  If you have a choice between
a signal (color 1) and a delayed form of itself (color 15), the second
one will be delayed, no?  :)

Seriously, a picture might help.  Below, I've drawn a few periods of
a sinewave.  Each period corresponds to one pixel on screen.  I've
assumed that the delay for color 15 is 360 degrees, so that it lines
up with color 1.  For colors 2 and 3, you can see the delay building up.
For color 15, the delay is an entire pixel displaced.

-         -         -         -
/ \       / \       / \       / \
/   \     /   \     /   \     /   \               color 1
\   /     \   /     \   /     \   /
\ /       \ /       \ /       \ /
-         -         -         -
-         -         -         -
/ \       / \       / \       / \
/   \     /   \     /   \     /   \              color 2
\   /     \   /     \   /     \   /
\ /       \ /       \ /       \ /
-         -         -         -
-         -         -         -
/ \       / \       / \       / \
/   \     /   \     /   \     /   \             color 3
\   /     \   /     \   /     \   /
\ /       \ /       \ /       \ /
-         -         -         -

(...colors 4-14......)

-         -         -         -
/ \       / \       / \       / \
1 pixel  /   \     /   \     /   \     /   \      color 15
<------->      \   /     \   /     \   /     \   /
delay         \ /       \ /       \ /       \ /
-         -         -         -
-         -         -         -
/ \       / \       / \       / \
/   \     /   \     /   \     /   \       1 pixel   color 1
\   /     \   /     \   /     \   / <------->
\ /       \ /       \ /       \ /    delay
-         -         -         -

This is clearly visible on a real display.  It's what causes the artifacts
at vertical edges.  No big deal, but it's important to keep in mind when
putting similar colors next to each other.

-Chris

On Thu, 14 Jul 2005, Eric Ball wrote:

> 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.

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