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

[Michael Williams]

Sorry for the late reply all.  Been having severe trouble with my  
hosting.  Anyway, just wanted to drop a quick "Thank you" to  
everyone; specifically Maren, Bill, Rob, and Mark (*especially Rob  
and Mark; hillarious and informative).  I'll look into all the  
suggestions and hopefully post something worth reading soon.  All the  
best.

Regards,
Michael


On Aug 27, 2007, at 9:20 PM, Mark Calabretta wrote:

>
> On Mon 2007/08/27 11:32:19 -0400, Michael Williams wrote
> in a message to: Thierry Forveille <Thierry.Forveille at obs.ujf- 
> grenoble.fr>
> and copied to: fitsbits at donar.cv.nrao.edu
>
> Michael,
>
> The "I" in FITS originally stood for "Image", now it really stands for
> "Information".  To get a better understanding of what FITS is about I
> suggest installing 'fv' and using it to explore its test files and a
> selection of FITS files that you gather from the internet.  fv can
> display astronomical data as images, plots, histograms, etc as
> appropriate.  In fact, I doubt that there is anything that you would
> want to do with a general FITS file that fv doesn't already do,
> http://heasarc.gsfc.nasa.gov/docs/software/ftools/fv/
>
> To get a better understanding of the visualization aspects, try
> installing Karma and use 'kvis' and 'xray' to play with 2D or higher
> dimensional images (not binary tables, etc.).
> http://www.atnf.csiro.au/computing/software/karma/
>
> To view general images with proper world coordinate handling, try
> ds9: http://hea-www.harvard.edu/RD/ds9/
>
>> 1)  Is a FITS file really similar to, say, a Microsoft Word =20
>> document. . .in that it can store *any* kind of data (images,  
>> mp3s, =20
>> pdfs, minivans) with the only thing that can be counted on being  
>> the =20
>> "standard" header?  It seems that my problem is the fact that I'm =20
>> expecting FITS to actually *fit* (pun intended) into some specific  
>> =20
>> category with absolutely specific syntactical and semantic  
>> requirements.
>
> In some respects FITS is a bit like the Roman alphabet, it only  
> provides
> a framework for communication.  Knowledge of the Roman alphabet allows
> you to read something written Italian, German, French, etc. without
> understanding what the words mean.  It doesn't work so well for  
> English
> or Polish which should give you an idea of how FITS, likewise, has  
> been
> corrupted by usage!  Various garnishes, accents and the like, that  
> have
> been added to the Roman alphabet in some languages also have an  
> obvious
> parallel in everyday FITS.
>
> FITS does also have some semantic content that is interpretable by
> software, mainly associated with the interpretation of physical
> measurements.  However, most of FITS' semantic content is really only
> understood by software written by the originators of the FITS file,
> and also by humans reading the comments in the header.
>
>> 2) What is the significance of *any* imagery in FITS?  Are the  
>> images =20=
>>
>> literally live pictures that were taken, or some arbitrary  
>> graphical =20
>> representation of data?
>
> Two examples:
>
> 1) Rotational synthesis radio telescopes don't "take photos" in
> the same sense that some optical telescopes do.  They measure the
> components of the Fourier transform of the sky brightness distribution
> ("visibilities") and these are later synthesised into an image.
> FITS can store both the visibilities and the image.  The resulting
> image can certainly be "viewed" but it is a visual representation of
> something that cannot be seen.  Such images typically have artifacts
> that require special algorithms to remove.  The purpose of generating
> such images is usually to measure the brightness and the precise
> position on the sky of particular radio sources.  Images of extended
> sources taken at different wavelengths are sometimes compared - these
> may contain profound astrophysical content, e.g.
> http://antwrp.gsfc.nasa.gov/apod/ap020920.html
> http://antwrp.gsfc.nasa.gov/apod/ap020812.html
>
> 2) The detectors on board an orbiting gamma-ray telescope record the
> direction and strength of each incoming photon.  These individual bits
> of data can later be combined into a type of 2D histogram, a sort of
> "image", showing where the photons came from.
>
> Have a look through the backlog at "Astronomy Picture of the Day" for
> further examples.  Today's just happens to be aposite.
> http://antwrp.gsfc.nasa.gov/apod/astropix.html
>
>> 3) How do I determine what type of image manipulations are  
>> legitimate =20=
>> for any type of image data?  Should I allow sepia toning?  Should  
>> I =20
>> allow them to run photoshop filters on the pictures?  I mean,  
>> what, =20
>> really is the usefulness of any manipulation on the image and what  
>> =20
>> are the most common techniques?
>
> Play with the image display options in kvis, I think you'll get the
> idea pretty quickly.
>
>> 4) What is the goal of scientists when it comes to examining =20
>> another's FITS files?  What kind of "information" is truly  
>> gathered =20
>> from the "data"?
>
> In a nutshell, the basic aim is to understand the origin and evolution
> of the universe.
>
> Mark Calabretta
> ATNF
>