Subject: FITS data question

From: gregg at hcirisc.cs.binghamton.edu (Gregg W. Riedel)
Date: 15 Sep 1994 07:01:56 GMT

Hi!
   I'm a graduate student in computer science, with zero knowledge of
astronomy.  I am implementing a FITS reader for an image processing
package.

   I have fetched a test image from the Hubble telescope of Saturn
(w0ck0101t_c0h.fit), and I noticed that the FITS data is broken into
3 axes (800 x 800 x 4); these are apparently separated image planes.
The questions:  what kind of separation is used (RGB?, CMYK, other?),
and where in the file might I find this information?  Is there a
standard for color images?  The literature seems to point toward all
"images" as being greyscale.

   Please forgive my misuse of FITS terminology; I understand the extreme
flexibility of this format, but am solely interested in getting some
pictures :)

Thanks!
Gregg
---------------------------------------  //  --------------------------------
Gregg William Riedel                    //              Binghamton U. - MS-CS
consp24 at bingsuns.pod.binghamton.edu \\ // Amiga        Sr. Systems Consultant
gregg at HCIRisc.cs.binghamton.edu      \X/ 4000/040        ImageFX 2.0 Dev Team
-----------------------------------------------------------------------------

--
---------------------------------------  //  --------------------------------
Gregg William Riedel                    //              Binghamton U. - MS-CS
consp24 at bingsuns.pod.binghamton.edu \\ // Amiga        Sr. Systems Consultant
gregg at HCIRisc.cs.binghamton.edu      \X/ 4000/040        ImageFX 2.0 Dev Team
-----------------------------------------------------------------------------

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From: carl at SOL1.GPS.CALTECH.EDU (Carl J Lydick)
Date: 15 Sep 1994 22:00:27 GMT

In article <GREGG.94Sep15030157 at hcirisc.cs.binghamton.edu>, gregg at hcirisc.cs.binghamton.edu (Gregg W. Riedel) writes:
=
=Hi!
=   I'm a graduate student in computer science, with zero knowledge of
=astronomy.  I am implementing a FITS reader for an image processing
=package.
=
=   I have fetched a test image from the Hubble telescope of Saturn
=(w0ck0101t_c0h.fit), and I noticed that the FITS data is broken into
=3 axes (800 x 800 x 4); these are apparently separated image planes.

Er, no.  They're images from each of four separate CCDs, not four separate
colors.  All images from the HST are monochromatic, in that they're images
taken through a specific filter.

=The questions:  what kind of separation is used (RGB?, CMYK, other?),
=and where in the file might I find this information?  Is there a
=standard for color images?  The literature seems to point toward all
="images" as being greyscale.

The images ARE greyscale.
--------------------------------------------------------------------------------
Carl J Lydick | INTERnet: CARL at SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL

Disclaimer:  Hey, I understand VAXen and VMS.  That's what I get paid for.  My
understanding of astronomy is purely at the amateur level (or below).  So
unless what I'm saying is directly related to VAX/VMS, don't hold me or my
organization responsible for it.  If it IS related to VAX/VMS, you can try to
hold me responsible for it, but my organization had nothing to do with it.

---

From: hanisch at stsci.edu (Bob Hanisch, ST ScI)
Date: 15 Sep 1994 16:52:05 GMT

Images from HST's Wide Field/Planetary Camera consist of four separate CCD
frames -- these are the four images you are seeing stacked in the FITS file.
They do not form a color composite or anything.  The four frames are stored
this way (actually, only one of several options available to HST users) 
purely as a matter of convenience.  Each image has coordinate information
in the header that describes the orientation and position of each frame.
They can be pasted together brute-force to make a mosaic, but to do this
properly requires eliminating region along the edges of each chip that is
unilluminated, and then geometrically correcting three of the four frames
to account for the slight misalignment of the detectors.

_______________________________________________________________________________
Robert J. Hanisch                       Tel. (410)338-4910   Fax. (410)338-5090
Space Telescope Science Institute       NSI: hanisch at stsci.edu [130.167.1.2]
3700 San Martin Drive                   DECNet: STSCIC::HANISCH [6549::] 
Baltimore, MD  21218  USA