Subject: Re: HST images of Io

From: bschlesinger at nssdca.gsfc.nasa.gov (Barry Schlesinger)
Date: Tue, 31 Mar 1992 18:50:00 GMT

In article <1992Mar31.163809.9182 at elroy.jpl.nasa.gov>, baalke at kelvin.jpl.nasa.gov writes...
 >
 >I understand that the Hubble images are in a slightly different FITS format
 >than your standard FITS image.  

I would say, rather, that they are in standard FITS format, but not 
stored as a simple two-dimensional array.

 >I don't know exactly what the difference is,
 >but the Hubble FITS seems to be split into four parts,

What is happening is that a 1600x1600 image is being split into four 
pieces and stored as an 800x800x4 array.  One can merge the four 
quarters back into the original picture if one knows how it was done.

 >and seems to be
 >taking advantage some part of the FITS standard not normally used.

This particular division in four is not common usage.  But it is not
unusual for FITS primary data arrays to be of more than two
dimensions.  For multicolor maps, one frequent approach is to make
color the third dimension. 

 >Being own of the programmers of IMDISP, I was well aware that IMDISP wouldn't 
 >display the Hubble images, though it would display other FITS images 
 >... 

I can't speak to IMDISP specifically, but many of the packages that
convert FITS arrays to pictures can't handle arrays of more than two
dimensions (NAXIS>2).  Even for those that can, the best one could
reasonably expect would be four quarter pictures, as a general package
would not recognize the particular Hubble organization.

				Barry Schlesinger
				NSSDC/NOST FITS Support Office

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From: uk1 at spacsun.rice.edu (Paul A. Scowen)
Date: 31 Mar 1992 19:51:57 GMT

The HST images available on the s.a.h. anonymous archive were provided by Ed 
Groth of the Princeton group, and are in GIF format.  Several viewers exist for
this type of image including xv and xloadimage.  For your info, the available
images and accompanying file are:

crsplit.ps.Z	compressed Postscript file containing a paper on Cosmic-Ray
		rejection in WFPC images, by Ed Groth at Princeton.

eta_carina.gif	public domain image of the Eta Carina Nebula (GIF format)

hstori*		public domain emission line image of the Orion Nebula, and
		accompanying documentation explaining the format of the image

jupiter.gif	public domain image of Jupiter

n1275.gif	PD image of NGC 1275

satws*		several PD images of the storm observed on the surface of Saturn
		by the Space Telescope, together with explanatory notes (.doc)

-- 
--------------------------------------------------------------------------------
Paul A. Scowen					INTERNET: uk1 at spacsun.rice.edu
Department of Space Physics & Astronomy		DECnet:   RICE::SCOWEN
Rice University, P.O. Box 1892			Tel:      (713) 527-8101 x2433
Houston, TX 77251-1892				FAX:      (713) 285-5143
--------------------------------------------------------------------------------

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From: warnock at nssdca.gsfc.nasa.gov (Archie Warnock)
Date: 31 Mar 92 21:32:00 GMT

In article <1992Mar31.094131.1 at vaxr.sscl.uwo.ca>, stooke at vaxr.sscl.uwo.ca writes...
>SAOIMAGE on a DECstation.  The other images, one a 'fake' and the other two
>the HST images after reconstruction, could not be displayed in either
>IMDISP or SAOIMAGE.  Can anybody who has looked at these images indicate
>to me how I might be able to display them?  Thanks....

Mystery apparently solved via E-mail.  Phil tells me that the other 
images have BITPIX=-32, indicating they are floating point data, under 
the IEEE agreement.  IMDISP doesn't do floating point images - at least, 
not yet.  We're working on a (hopefully) rational approach to scaling 
them down to 8-bit integers for display, particularly in the absence of 
scale factors in the header.  Any suggestions?

----------------------------------------------------------------------------
-- Archie Warnock                     Internet:  warnock at nssdc.gsfc.nasa.gov
-- Hughes STX                         SPAN:      NSSDC::WARNOCK
-- NASA/GSFC                          "Hail To The Redskins!"