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From: rrw@naucse.UUCP (Robert Wier)
Newsgroups: comp.sys.mac,comp.sys.mac.programmer,comp.graphics
Subject: AppleScan Dithering?
Message-ID: <1409@naucse.UUCP>
Date: 3 May 89 23:28:10 GMT
Organization: Northern Arizona University, Flagstaff, AZ
Lines: 24



 Has anyone out there using an Apple Scanner with a LaserPrinter
 found the "magic" number for doing enlargements without generating
 objectionable dithering aliasing.  If you scan a picture at 300 dpi,
 and print it at, say, 200% you get WEIRD patterns because of the
 overlapping dither patterns.  Through trial and error (mostly error)
 I have found that 175% works pretty well.  

 I would assume that this could be calculated if you knew what AppleScan
 was doing with it's dithering technique. However, as of yet, I havn't
 been able to figure out why 175% works pretty well, while 200% is 
 unusable.  I assume that the "magic" enlargement numbers would be
 somthing where a common factor is the 300 dpi scan resolution, and the
 (4x4? 5x5? 8x8?) dithering algorithm.
 
 If you can help, please post here or E-Mail to me and I will post
 a summary to the net.

 THANKS!

   - Bob Wier                                College of Engineering
  Flagstaff, Arizona                      Northern Arizona University
  ...arizona!naucse!rrw |  BITNET: WIER@NAUVAX | *usual disclaimers*