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Technology Stocks : Silicon Graphics, Inc. (SGI)
SGI 91.87+1.8%Dec 5 9:30 AM EST
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To: Alexis Cousein who wrote (6125)5/27/1999 3:15:00 PM
From: brushwud  Read Replies (1) of 14451
 
Antialiasing can be done by pre-filtering or post-filtering. Your explanation pertains to post-filtering:

> Anti-aliasing is a method by which a pixel colour is determined by
> sampling more than one subpixel (with fractional coordinates) and
> averaging.

Pre-filtering, in theory, would accumulate contributions from all surfaces which contribute to a given pixel, but in practice, might accumulate contributions from some subset of such surfaces. Pre-filtering tends not to have the visual artifacts of the post-filtering approaches based on subpixel sampling. But "stochastic" sampling can reduce artifacts by sampling randomly (or pseudo-randomly), not on a regular grid.

> as an example, a TV has only roughly 500 lines of video, but no
< aliasing artefacts -- and you'll note that you neither see jaggies
> or creepies when watching a movie ;)

You can certainly see artifacts of scan lines on TV. Perhaps the jaggies don't catch your eye because of the 30 Hz (U.S.) frame rate, but if you look at a still frame, you can find them. Vertical artifacts may be less pronounced because of the analog character of TV. Often if talking heads are wearing thin-striped ties or shirts, they turn into sparkling psychedelic rainbows because of aliasing.
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