Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!usc!apple!netcom!amdcad!dgcad!dg-rtp!bigben!bigben!philip From: philip@beeblebrox.dle.dg.com (Philip Gladstone) Newsgroups: comp.compression Subject: Re: Atronomical data compression Message-ID: Date: 24 Mar 91 22:42:05 GMT References: <1991Mar23.013557.28151@nntp-server.caltech.edu> Sender: usenet@dle.dg.com (Net News) Organization: Data General, Development Lab Europe Lines: 38 In-Reply-To: sns@lo-fan.caltech.edu's message of 23 Mar 91 01:35:57 GMT >>>>> On 23 Mar 91 01:35:57 GMT, sns@lo-fan.caltech.edu (Sam Southard Jr.) said: Sam> I have a topic/question that should be suitable for this newsgroup. I am a Sam> software engineer working on the software for the Keck Telescope (the new 10m Sam> in Hawaii). One of the things I am doing is taking the data from the CCD to Sam> a VMEbus controller crate (Sun 1E running VxWorks) and from there to a Sam> Sun 4/470 over the ethernet. Sam> I have thought of a few methods which I can try, but I am interested in looking Sam> at as many ways as possible. I have lots of actual data to try out various Sam> compression methods, and a reasonable amount of CPU to burn in choosing the Sam> algorithm (or two or three) which will actualyl be used. Sam> Does anyone have any suggestiongs? The first question that comes to mind is whether you want a lossless scheme or a lossy scheme? If you want lossless compression, then I must ask you why? You already admit that there is noise in the input signal and I bet you get noise introduced from atmospheric turbulence. If you want lossy compression, then you have to decide how much loss you are prepared to accept, In general the lossy alogorithms do much better at compressing pictures than the lossless ones. The improvement can be a factor of 10 better. The whole issue of whether lossy as opposed to lossless compression is 'better' is being discussed ad nauseam in various other groups, so I don't want to start it here. But the question as to which is appropriate for particular applications is relevant. Philip -- Philip Gladstone Dev Lab Europe, Data General, Cambridge, UK "I really wish I'd listened to what my mother told me when I was young." "Why, what did she tell you?" "I don't know, I didn't listen."