Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!uunet!bywater!arnor!arnor!victor From: victor@watson.ibm.com (Victor Miller) Newsgroups: comp.compression Subject: Compression figures Message-ID: Date: 15 Apr 91 15:40:57 GMT Sender: news@watson.ibm.com (NNTP News Poster) Reply-To: victor@watson.ibm.com Distribution: comp Organization: IBM, T.J. Watson Research Center Lines: 28 Nntp-Posting-Host: irt I've just come back from DCC '91 (which was a pretty good conference), and was reminded of one of my pet peeves: reporting compression figures. There doesn't seem to be any standard way. The following seem to be in use: (Orig = original size, New=compressed size) 1) Orig/New 2) New/Orig 3) (Orig-New)/Orig 4) Orig/(B*New) Here B is either the byte size (as in bits/byte) or the number of bits/pel (as in bits/pel). In addition, 2 and 3 are often reported as percentages, without specifying the % sign. I really don't like 3): it gives the amount saved. It does have the property the the bigger the value, the better compression. I actually favor 4), because it gives a normalized measure of compression: it doesn't matter what the byte size is: if you have 7 bit bytes, or 8 bit bytes the figure comes out the same. On the other hand, 1) isn't too bad, since it gives a larger figure for better compression. At the very least, I would plead with people reporting compression figures explicitly to give the method they use in calculating these results, since there isn't any standard. -- Victor S. Miller Vnet and Bitnet: VICTOR at WATSON Internet: victor@watson.ibm.com IBM, TJ Watson Research Center