[fitsbits] Question(s) regarding development of proprietary FITS manipulation software. . .

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On Mon, 27 Aug 2007, Michael Williams wrote:

> 1)  Is a FITS file really similar to, say, a Microsoft Word document. 
>    . .in that it can store *any* kind of data

Well, most dead astronomers will revolve in their grave hearing a 
comparison of FITS with Microsoft Word (fortunately most FITS people 
are kicking and alive, and they will complain too), but in a sense yes, 
a FITS file can be a generic container. It is used as a container for

  - sky images [I]
  - detector images [I]
  - any other sort of image data [I]
  - astronomical catalogues [A,B]
  - astronomical spectra  [B,I]
  - time series [B]
  - photon lists [B]
  - detector response matrices [B]
  - any tabular data (typically an instrument calibration data) [B]
  - or even an index to a collection of other FITS files (e.g. the 
    XMM calibration index file) [B]

These are all real examples I've encountered. [I],[A],[B] means they can 
be images, ascii tables, binary tables. See my former posting.

> 2) What is the significance of *any* imagery in FITS?  Are the images
> literally live pictures that were taken, or some arbitrary graphical
> representation of data?

Most images are derived somehow from raw images. When not, ok they may 
fit in your category of "arbitrary graphical representation" ... if I 
put in a FITS image the value of chi-square vs spectral index on the x 
axis and hydrogen column density on the y axis.

Raw images are some form of intensity (roughly proportional to light 
intensity or number of photons) collected on some detector (a CCD, a 
photographic plate or whatsoever) as function of pixel xy position.

In most cases this corresponds to an actual picture of the sky in some 
band but calibration of intensity of even xy can be tricky.

But in other cases what is on the detector comes from the sky but is 
something else (e.g. a collection of spectra, see e.g.
http://www.oamp.fr/virmos/vvds.htm)
 
> 3) How do I determine what type of image manipulations are legitimate 
>    for any type of image data?  Should I allow sepia toning?  Should I 
>    allow them to run photoshop filters on the pictures? 

I would say in general no. You can, perhaps do that to make a figure 
(the GIMP reads FITS files), but in general the typical FITS image 
display (ds9) will first scale the image data somehow (they are data in 
physical units !!). And most programs do analysis without display.

Ask your client what he wants !!!

> 4) What is the goal of scientists when it comes to examining another's FITS
> files?  What kind of "information" is truly gathered from the "data"?

Too long to explain ... have to go home now


> On Aug 27, 2007, at 11:12 AM, Thierry Forveille wrote:

> > you attend/read an Astronomy 101/Philosophy of Science 101

Whatt's this 101 ? Dalmatian dogs ? :-)


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