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From: scott@applix.UUCP (Scott Evernden)
Newsgroups: comp.graphics
Subject: Scaling dithered images
Message-ID: <627@applix.UUCP>
Date: Tue, 1-Dec-87 13:10:34 EST
Article-I.D.: applix.627
Posted: Tue Dec  1 13:10:34 1987
Date-Received: Fri, 4-Dec-87 07:10:06 EST
Reply-To: scott@applix.UUCP (Scott Evernden)
Organization: APPLiX Inc., Westboro MA
Lines: 24


I have a 300dpi monochromatic image from a MicroTek scanner.
The image is a halftone, meaning the scanner has imposed a
regular dither pattern (variable: 2x2 to 8x8) to achieve grey scale.

I want to display this image on an approx. 75dpi screen.
Currently, I take the simple approach of resampling the
original image according to the scale factor (300/75) and
read the value of the closest pixel.

As you might guess, some very bad artifacting occurs.

I suppose I could average the pixels in the vicinity of the
sample location and maybe reduce my problem.

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.

Ideally, the algorithm should be amenable to rotation and shearing
transforms as well.

-scott