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From: jbm@aurora.UUCP (Jeffrey Mulligan)
Newsgroups: comp.graphics
Subject: Re: Scaling dithered images
Message-ID: <1369@aurora.UUCP>
Date: Fri, 4-Dec-87 14:21:05 EST
Article-I.D.: aurora.1369
Posted: Fri Dec  4 14:21:05 1987
Date-Received: Wed, 9-Dec-87 04:50:16 EST
References: <627@applix.UUCP>
Organization: NASA Ames Research Center, Mt. View, Ca.
Lines: 34

in article <627@applix.UUCP>, scott@applix.UUCP (Scott Evernden) says:
> 
> 
> Question is:  does anyone have any neat ideas or references on
> how to display hi-res dithered images on a low-res screen at any
> scale factor?  I'm looking for image scaling algorithms which can
> avoid the artifacting problem.
> 

The following approach is probably a little expensive computationally
(i.e. slow) but it should work:

	1)  Low pass filter the original dithered image

		Now you have a continuous tone image which
		approximates the original.  The filter should
		be designed to cut out everything above
		the Nyquist frequency of the final sampling rate.

	2)  Subsample this intermediate image.

		Since you have filtered, the subsampling will
		not introduce any aliases (presumably the type
		of "artifacts" you observed?).

	3)  Dither the subsampled image.



-- 

	Jeff Mulligan (jbm@ames-aurora.arpa)
	NASA/Ames Research Ctr., Mail Stop 239-3, Moffet Field CA, 94035
	(415) 694-5150