Subject: Re: Data Compression

From: Vaclav Pribik <emorse at csn.net>
Date: 26 Nov 1995 00:07:04 GMT

Data compression is useful a mos on Internet (smaller down-uploading times). 
There are (I think...) two different ways:

1. Use uncompressed FITS and compress it (the best should be comrpess it bu 
Compress (.Z), UNIX is still standart). Then, after downloading, uncompressed 
again and easy-to-work FITS is avaible. Problem: Software depended

2. Use directly some compression method:

RLE (like IFF, Tiff) or
LZW (like GIF89a )      - no quality lost
or
Frequence chart (like JPEG) - some quality lost, but high-compressive. The 
result-size is not (= only a little) depending on size. (I tried it - image 
1280x1280 pix was 1.5 bigger than the some image, only 320x320 pix.).

+: No SW depend
Problem: Harder to process.

The first method is easier (everyone has, or can have, Compress), but it is not 
so compressive than method 2. Maybe it will be useful to make new extension using 
method 2, but it should be used only for large images (ex. 16777216x8388608 
pixels :-) ), that is suitable for JPEG. Only the optimisation should be low = 
most quality. And the format should be also modified - JPEG is for COLOR images 
and don't like gray-scaled.

Vaclav Pribik
email now: emorse at csn.net
normal email, use from 7/96: pribik at leo1.zlin.vutbr.cz
astro home page: http://www.csn.net/~emorse/haf/haf.html

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