Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!ptimtc!nntp-server.caltech.edu!madler
From: madler@nntp-server.caltech.edu (Mark Adler)
Newsgroups: comp.compression
Subject: Re: JPEG compression errors ?!
Message-ID: <1991Jun11.021223.29209@nntp-server.caltech.edu>
Date: 11 Jun 91 02:12:23 GMT
References: <1991Jun4.223719.2958@qualcomm.com> <D88-JWA.91Jun5105246@byse.nada.kth.se> <4022@sixhub.UUCP>
Organization: California Institute of Technology, Pasadena
Lines: 12

The talk about JPEG being acceptable or not seems to imply that there
is a such a thing as "the" JPEG.  There isn't.  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).  Setting these parameters is still rather a black art,
but up to a point, you have control over the resulting quality of the
decompressed images.

Mark Adler
madler@tybalt.caltech.edu