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> <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