Newsgroups: sci.image.processing
Path: cantaloupe.srv.cs.cmu.edu!das-news2.harvard.edu!news2.near.net!MathWorks.Com!panix!zip.eecs.umich.edu!newsxfer.itd.umich.edu!gumby!yale!yale.edu!noc.near.net!analog.com!analog.com!nwd2sun2.analog.com!az
From: az@saturn.analog.com (Alex Zatsman)
Subject: Re: Anti-aliasing algorithm
In-Reply-To: tyin@netcom.com's message of Wed, 12 Oct 1994 01:03:38 GMT
Message-ID: <AZ.94Oct12114626@saturn.analog.com>
Sender: usenet@analog.com
Organization: Analog Devices Inc, Norwood MA, USA
References: <tyinCxJCA2.Ay0@netcom.com>
Distribution: usa
Date: Wed, 12 Oct 1994 16:46:26 GMT
Lines: 33

In article <tyinCxJCA2.Ay0@netcom.com> tyin@netcom.com (David Yin) writes:

>      I hope this is the right group I posted.
>      I want to know what is the anti-aliasing algorithm and how does it
>    work on color images? Does anyone know any reference or article/book
>    talking about this? any hint is appreciated.


If you have a straight edge in a low-resolution picture, it looks like
a sawtooth because the sampling  frequency (i.e. the resolution of the
picture) is too low for the frequency  involved (the 2D  step function
for the edge).

Antialising in this case is usually done by filling shades between the
teeth.   If you can get   the  same  picture (for   example,  if it is
synthetic image  like in ray  tracing or drawing programs) you compute
those shades by averaging or otherwise interpolating the colors in the
pixels in question.  In the example below  'H'  shows original pixels,
while the dots ('.') are for "shady", or anti-aliasing, pixels.


Before		After

HHHHH           HHHHH.   
HHHHHH      	HHHHHH.     
HHHHHHH     	HHHHHHH.    
HHHHHHHH    	HHHHHHHH.   
HHHHHHHHH  	HHHHHHHHH.   
HHHHHHHHHH 	HHHHHHHHHH 

--
Alex Zatsman,     Analog Devices, Inc., (617) 461-3729
alex.zatsman@analog.com
