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From: ge@dbf.kun.nl (Ge' Weijers)
Newsgroups: comp.compression
Subject: Re: Compression for LINE DRAWINGS?
Message-ID: <2909@wn1.sci.kun.nl>
Date: 3 Apr 91 09:52:41 GMT
References: <1991Mar30.210354.8076@cec1.wustl.edu>
Sender: root@sci.kun.nl
Lines: 31

aj6818@cec1.wustl.edu (Albrecht!) writes:

>I need some suggestions for compression of B/W line drawings for an on line
>data base.  I don't care if the compression is slow, but I would like to 
>do decompression on the fly and directly to the screen.  A slightly lossy
>technique would be OK as the original images aren't all that good.  

>With so much white space there has got to be something that will be fairly
>compact!!

If you're pictures are fairly simple a compression scheme like runlength
encoding should give good performance. You might want to try the
scheme used in fax machines. See
	
	International Digital Facsimile Coding Standards
	Roy Hunter and A. Harry Robinson
	Proceedings of the IEEE, vol. 68, no. 7, july 1980

which describes the group-3 fax coding procedure, a.k.a. the MREAD
algorithm. It uses Huffman codes to compress the run-lengths.
You can simplify the algorithm somewhat for your purposes as you do not
need to recover from communication errors (i.e. only use the two-dimensional
compression, assuming the actual image is preceded by a blank line).

Ge' Weijers

--
Ge' Weijers                                    Internet/UUCP: ge@cs.kun.nl
Faculty of Mathematics and Computer Science,   (uunet.uu.net!cs.kun.nl!ge)
University of Nijmegen, Toernooiveld 1         
6525 ED Nijmegen, the Netherlands              tel. +3180652483 (UTC-2)