Subject: Data Compression

From: "Dr. Immanuel Freedman" <immanuel at mother.com>
Date: 3 Nov 1995 23:51:18 GMT

Colleagues

This is a posting to open discussion about Data Compression within the 

FITS Standard.  It is a continuation of the topic presented at the ADASS V

FITS BoF session.

What do the readers of this group feel about the need for data compression, now 

that several major projects have already adopted such techniques both onboard

(Galileo, Mars Observer...) and for browse/archival (Space Telescope...) ?

Dr. Immanuel Freedman
immanuel at mother.com

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From: Lucio Chiappetti <lucio at ifctr.mi.cnr.it>
Date: Thu, 16 Nov 1995 09:33:00 +0100 (MET)

On 3 Nov 1995, Dr. Immanuel Freedman wrote:

> FITS Standard.  
  [...]
> What do the readers of this group feel about the need for data compression,

  Personally as an user, it is something I'd never like to see as an
  "extra feature" in data I'd receive, I'd have to handle or I'd produce,
  and which shall force usage of "additional software".
  (I'm quite happy with "standard Unix compress" of "plain FITS files",
  inefficient it may be for some astronomical applications).

  This does not mean large projects shall not use it in their archiving,
  but this shall be made transparent to the user (e.g. include uncompressing
  ready-to-use "viewer" at the browser end)

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From: "Dr. Immanuel Freedman" <immanuel at mother.com>
Date: 16 Nov 1995 20:18:00 GMT

Colleagues

Indeed, this transparency is EXACTLY what I'm proposing and has been 
implemented as an experiment in the COBE project & NITFS. We should be able to
read/write & manipulate data in compressed/structured form without additional
overhead.

However, we spend YEARS defining our data structures for processing & analysis
for many large-scale or archival projects and the overhead of assigning
compression methods is very small by comparison.

I propose a compressive class library, implemented "underneath" the data base
so that we may declare data to be of compressed/structured class or type
and the compression/decompression/manipulation takes place through the
implemented member functions of the class,

Thanks for your input,

Dr. Immanuel Freedman
(916) 759 8673