Re: mark iv compression

[hjohnson@pluto.njcc.com (Herbert R Johnson)]

On Tue, 06 Jun 2000 17:16:23 -0700, Chris Albertson <calbertson@logicon.com> wrote:
*>
*>One thing I thought of that I'll ssuggest we concider:  I seems that we all
*>want to keep the raw image data, Tom is keeping it just as it came off
*>the camera and Arne has suggested after 10X compression.  After reading
*>Jures tech note I thinkg we should at least modify the header to include
*>corrected WCS (ra, dec, image scale and rotation and maybe more) before
*>the data is archived.
*>> 
*>  Chris Albertson

Some of you may recall I have a Tech Note on compression, written before
Mark IV data was available. While I've updated the references in it,
I have a bit more information to include which I will add shortly.

I've reviewed our recent correspondence on compression: I don't see offhand
any references to compression tests with current Mark IV data. I may have missed
something, I'd appreciate any info sent to me so I can add it to my
Tech Note. (My review was cursory, no offense if I missed some recent work.)

But my impression is that NOW is the time to test the "new"
uncoma-ed Mark IV image data for compressibility, if one or more sets
of reduction tools and/or programs are available for A - B testing.
That is, results from compressed vs. noncompressed images. The Tech
Note I believe will suggest the kinds of testing done previously on Mark III.
While it suggests methods, I would expect different results.

Tom's recent suggestion was *not* to keep the entire image, but to keep
the pixels measured ONLY. In effect, compressing the image "array" to only
those components which contribute to starlists, if I read his suggestion
correctly. One could do the arithmetic, but I would guess that would be
on the order of 10:1 compression. That too should be tested.

By the way, the local computer superstores have recently offered 20GB
or 30GB hard drives for $99. I will again suggest the least effort
kind of "archiving" may well be to fill up one of these drives and to
put it on the shelf, perhaps with a $10 '486 computer wrapped around it.
There will be no shortage of large, cheap hard drives and cheaper, previous-
generation computers.

Herb Johnson

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