Re: compression of Mark IV images

[Herb Johnson <hjohnson@pluto.njcc.com>]

Chris, if you keep track of the compression ratios of all the images
you compress and any other impressions you have, I'll add this info
to the TASS Tech Note on compression. While most of that note is oriented
to compressing raw data, more info is better. Thanks for your report.

Herb Johnson

Herbert R. Johnson              http://pluto.njcc.com/~hjohnson
hjohnson@pluto.njcc.com         voice 609-771-1503, New Jersey USA

             amateur astronomer and astro-tour guide
     classic S-100 computers restoration & parts as "Dr. S-100"
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          and senior engineer at Astro Imaging Systems

On Thu, 14 Sep 2000, Chris Albertson wrote:

> 
> Arne,
> 
> It takes me about two and a half minutes to down load
> each image.  Not bad.  That means I could transfer all
> of the raw data from a remote camera in real-time.  Still
> it could be better.  I used gzip to compress the files
> and notice they compres down almost 3:1.  It would be
> then, almost three times faster for all involved if you
> would compress the images at your end.  I just used
>   gzip --best xxxxx.yyy
> gzip is pretty universal and even people with Windows PCs 
> can read the .gz files
> 
> I was surprized to see that level of compression with a
> lossless compressor like gzip but I guess the dark/flat
> processing removes some noise and the full 16-bit pixel range
> is not used.
> 
> aah@nofs.navy.mil wrote:
> > 
> > I'm slowly transferring images onto our anon ftp site
> > (the link through the firewall is really slow).  The
> > files are 16bit FITS, on directory
> > ftp://ftp.nofs.navy.mil/pub/outgoing/aah/tass
> > with filenames like
> > 000911va.122
> > 000911vb.122
> 
> 
> 
> 
> > ...
> > 000911va.123
> > 000911vb.123
> > ...
> > where 122 = right ascension strip number
> > a-h are the individual frames within that right
> > ascension strip, and 'v' indicates V-bandpass.
> > These frames are all dark subtracted, trimmed and flattened.
> > The Right Ascension for 122 is about 01:44, and
> > for 123 is about 02:16.  The declinations are probably
> > north of -8 degrees and south of +40 degrees.  Other than
> > that, you are on your own to find where the TASS camera
> > was pointed!
> >   The GRB was at 02:18:42 +07:48:30.  The frame that
> > should have covered that field is 000911ve.123, but I
> > couldn't identify the field.  I think the drive got
> > stuck at pretty high declination, but that is a guess.
> > The ftp process just finished 000911vb.123, taking
> > 3 minutes per frame to transfer!  Something has changed
> > on our internal network, and I'll have to complain to
> > the sysadmin tomorrow.
> >   It is clear again tonight; I'll be taking a couple of
> > hours on CY Aqr before continuing the photometric survey.
> >   Richard C. has offered to identify these fields, but
> > I think the more brainpower the better.  It is kinda fun
> > to be using the BD charts after 30 years.  We don't even
> > own a Millenium atlas here, but that would be just about
> > ideal for the Mark IV.
> > Arne
> 
> -- 
>    Chris Albertson             home: chrisja@phoenixdsl.com  
>    Redondo Beach, California   work: calbertson@primeadvantage.com
> 
>