Re: [stella] interlace

Subject: Re: [stella] interlace
From: Glenn Saunders <cybpunks@xxxxxxxxxxxxx>
Date: Wed, 21 Jun 2000 21:31:02 -0700
At 10:54 PM 6/21/2000 -0500, you wrote:
But sprite flicker is kinda the same thing.  Example, that polo demo(I
don't remember the name).  I can't find it(I don't remember if I have a

Conceptually, yes, it is the same thing. 30hz flicker in a venetian blind sprite that alternates as Polo does is mimicking what NTSC interlace does, but with double the scanlines, mind you.

However, note that the background is stable on the VCS at 60fps.

Really?  I mean in interlaced mode, shouldn't it be doing the same as a tv
signal?  I've use a character generator that had very obvious pixals, one
per line, and it does not appear to flicker.

It's a somewhat subjective thing. Note that movies are 24fps, but I believe the projector shutter passes by the aperture twice per frame so you get the illusion of 48fps, but most people are so used to movies they don't notice the flicker. So for some people their persistence of vision makes it hard for them to notice 30hz NTSC interlace flicker. It's much more evident when you have a high contrast line, one with a light color taking up the upper field and one with a dark color on the next field. If you have a light color that is thick enough to go through both fields then you won't notice so much that on every other frame, one of the two fields is dark. But if you get your eye really close to the scanline, you'll see it.

Also note that character generators typically employ some sort of antialiasing and most text fonts have curves on most letters depending on the font. Even if it's a subtle bend or curve it can really help eliminate the perception of interlace flicker.

Nope, your right, it doesn't work.  Well, it doesn't hold the frame, it
scrolls quite abit...

It's because the VCR doesn't really know where the beginning and the ends of the frame are. The game isn't delivering a regular signal.

Glenn Saunders - Producer - Cyberpunks Entertainment
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