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From: sdh@joevax.UUCP (The Doctor)
Newsgroups: net.graphics
Subject: Possible way of anti-aliasing.
Message-ID: <280@joevax.UUCP>
Date: Wed, 17-Sep-86 13:34:27 EDT
Article-I.D.: joevax.280
Posted: Wed Sep 17 13:34:27 1986
Date-Received: Fri, 19-Sep-86 22:23:20 EDT
Distribution: net
Organization: Bell Communications Research Inc., Morristown, NJ
Lines: 35



I don't know a good algorithm for anti-aliasing, but you could try the
following technique:
Get a pixels attributes.  Average its attributes with the pixels
immediately tangent to it.  If the difference in attributes is above a
certain threshold, decide how greatly you want to change the pixel (could
be by a percentage of the difference in attributes.  If there is a change,
stack it, else nothing. Repeat until all pixels have been hit.  Go through
the stack and make the changes.

This should be very efficient on images with plenty of consistent background,
and not too many objects in the foreground.  It will use up more memory than
you'd really like on complex pictures.

Ways to eliminate this problem:

Forget the stack entirely and just put the image out to a file, or an
alternate graphics display.  This will have a memory consumption that will
be a constant, which is far smaller than the worst case of stacking.

Do separate passes for red, green and blue, thus reducing the data that has
to be stacked.

Don't do the whole screen in one pass.  Just do it in blocks of 3 scan lines
The reasoning behind this is that the fourth line down only needs to know
about line 3 and line 4, so it can forget about line 1 and 2.

I have no idea whether or not any of this is valid.  I started thinking about
anti-aliasing about 5 minutes ago, so this is just off the top of my head.
It seems to be a pretty brute force way of doing it, but swift.  If you
only stack 3 lines at a time, it will be very memory efficient too.

Steve Hawley
joevax!sdh