Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!cornell!batcomputer!itsgw!imagine!rpics!kyriazis
From: kyriazis@rpics (George Kyriazis)
Newsgroups: comp.graphics
Subject: Re: raytracing in ||
Keywords: 4 rays per pixel
Message-ID: <1877@imagine.PAWL.RPI.EDU>
Date: 29 Nov 88 05:06:14 GMT
References: <9700001@datacube> <3148@uoregon.uoregon.edu> <1351@umbc3.UMD.EDU> <5263@cbmvax.UUCP> <5548@thorin.cs.unc.edu>
Sender: news@imagine.PAWL.RPI.EDU
Reply-To: kyriazis@turing.cs.rpi.edu (George Kyriazis)
Organization: RPI CS Dept.
Lines: 28

In article <5548@thorin.cs.unc.edu> brown@tyler.UUCP (Lurch) writes:
>In article <5263@cbmvax.UUCP> steveb@cbmvax.UUCP (Steve Beats) writes:
>>If you sample the scene using one pixel per ray, you will get
>>pretty severe aliasing at high contrast boundaries.  One trick is to sample
>>at twice the vertical and horizontal resolution (yielding 4 rays per pixel)
>>and average the resultant intensities.  This is a pretty effective method
>>of anti-aliasing.
>
>From what I understand, the way to achieve 4 rays per pixel is to sample at
>vertical resolution +1, horizontal resolution +1, and treat each ray as a
>'corner' of each pixel, and average those values.  This is super cheap compared
>to sampling at twice vertical and horizontal.
>

There is another way to do antialiasing, used mainly with parallel alrgorithms,
since keeping track of what CPU calculated what pixel is a bit clumsy.
You shoot N rays somewhere in the pixel and then take the average of them.
The rays need to have a Gaussian spatial distribution to be better results.
Using that method no data sharing is necessary, and you get reasonably good
results.  Sampling too few times you get noise, not aliasing effects.
Sampling in too big an area (eg. the area of say 6*6 pixels instead of 
just 1) you get blurr.  Sometimes it's a useful effect.


  George Kyriazis
  kyriazis@turing.cs.rpi.edu
  kyriazis@ss0.cicg.rpi.edu
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