Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!think!ames!aurora!jbm 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