Re: [stella] Some Questions That Bug Me

Subject: Re: [stella] Some Questions That Bug Me
From: Glenn Saunders <cybpunks@xxxxxxxxxxxx>
Date: Sun, 24 Jun 2001 10:14:20 -0700
At 01:11 AM 6/24/2001 -0700, you wrote:
all-in-one deluxe video cards.  Also at 30 fps.  How many scanlines of
*real* information is that?  Is it more like 240 or 480?  And what does

It's hard to say. A lot of capture cards, knowing that they are going to only play back on progressive-scan rather than interlaced monitors (as most computer video modes are) will only scan in video at half-res. Computer monitors do not play back interlaced video very well, although DVD player software has some elaborate method of doing so.

Glenn mean by interlaced?  Does a video signal repeat the same information
twice so that the screen is updated at 60 fps?  Or is it new information
each time?  But updating every other scanline?

New information every field, alternating even and odd scanlines so that for any given field every other scanline is blank.

Video game consoles, until recently, all used a noninterlaced video mode that doesn't leave these gaps but sacrifices half the vertical resolution.

Nevertheless, the 480 pixels of vertical res of interlaced video is only when you take both fields into account. For any individual field there is only 240 pixels of vertical res and 240 missing scanlines, which is why framegrabs almost always look crappier than moving video. If there is any motion in the video it has to be de-interlaced which usually means just halving the vertical res. If it's a still, you can merge both fields to make one full-res video still. In many cases you can composite between both approaches in a framegrab and I guess some software these days can do that automatically. I don't know.

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