gauthier@ug.cs.dal.ca (Paul Gauthier) (05/05/91)
I'm interested in what the optimal method for compressing B/W fax images (for agruments sake we'll allow both Fine and Standard resolution, but this may not actually be the case -- comments?). I'm interested in pointers to code that I can use or documents which would detail the method. Also, what kind of compression ratio/effectivness/etc should I expect from the methods you suggest? (On a single page image 1728x2200 [Fine] or 1728x1100 [Standard]). Thanks, PG -- ============================================================================ Paul Gauthier | gauthier@ug.cs.dal.ca President, Cerebral Computer Technologies | tyrant@dalac.bitnet Phone: (902)462-8217 Fax: (send email first) | tyrant@ac.dal.ca
raymond@cosc.canterbury.ac.nz (cantva) (05/06/91)
From article <1991May5.160009.16327@cs.dal.ca>, by gauthier@ug.cs.dal.ca (Paul Gauthier): > I'm interested in what the optimal method for compressing B/W fax images Are you interested in compression, speed, or both? > I'm interested in pointers > to code that I can use or documents which would detail the method. Depends on above. Adaptive arithmetic for compression, run length for speed. > Also, what kind of compression ratio/effectivness/etc should I expect > from the methods you suggest? (On a single page image 1728x2200 [Fine] or > 1728x1100 [Standard]). Run length will yield about 7:1 compression (see G3 standard for more accurate assessment). A good adaptive arithmetic compressor will rarely do worse than 20:1. I have built an adative arithmetic compressor to compress fax images. It is resolution independant and will handle arbitrarily large fax images (as long as the memory holds out!). The test images I tried were about 1700x2300 (over an A4 page) (513216 bytes). The worst it has done is 20.5:1 (~25000 bytes) (full page of (dense) text) and the best is 171:1 (< 3000 bytes) (simple digram). These two are in the CCITT fax test documents (I forget the numbers). Raymond. -- Raymond Wilson. email: raymond@cosc.canterbury.ac.nz snail: c/- Computer Science Department, University of Canterbury, New Zealand.