Newsgroups: comp.compression
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!math.fu-berlin.de!fauern!faui43.informatik.uni-erlangen.de!mskuhn
From: mskuhn@immd4.informatik.uni-erlangen.de (Markus Kuhn)
Subject: Re: JPEG compression errors ?!
Message-ID: <1991Jun11.105802.1385@informatik.uni-erlangen.de>
Organization: CSD., University of Erlangen, Germany
References: <1991Jun4.223719.2958@qualcomm.com> <D88-JWA.91Jun5105246@byse.nada.kth.se> <4022@sixhub.UUCP> <1991Jun11.021223.29209@nntp-server.caltech.edu>
Date: Tue, 11 Jun 1991 10:58:02 GMT
Lines: 20

madler@nntp-server.caltech.edu (Mark Adler) writes:
>[in JPEG] You can set 
>the compression level (roughly) by varying the quantization parameters
>from no quantization (lossless decompression, up to round-off errors
>in the DCT), to a great deal of quantization, the latter resulting
>it really awful looking, blocky decompression (at about the 30:1 to
>50:1 level).

In addition, the JPEG standard describes an absolutly lossless method
that doesn't use DCT. Each pixel is predicted by the values of three of 
its neighbours. But this results only in a 1:2 (?) compression for moderatly
complex images.

Markus


---
Markus Kuhn, Computer Science student -- University of Erlangen, Germany
X.400: G=Markus;S=Kuhn;OU1=rrze;OU2=cnve;P=uni-erlangen;A=dbp;C=de
I'net: mskuhn@immd4.informatik.uni-erlangen.de
