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

[William Thompson]

Michael:

Formats like GIF and JPEG are designed such that the images are scaled into the 
8-bit 0-255 range used by computer displays, and are generally accompanied by 
color information, such as color tables or separate red-green-blue images.  As 
such, they are already prepared for direct imaging.

The data in FITS files, however, are generally not preprocessed for viewing. 
They are in the units needed for scientific analysis.  Such images usually need 
some additional processing in order to be easily viewed.  The simplest way to 
process the image is to rescale it, mapping the minimum value to 0 and the 
maximum value to 255.  That often works, but usually one has to tweak it to get 
a good image.  These are some examples of the kind of operations that a general 
FITS viewer would need to be able to do:

1.  Adjust the mapping from image values to displayed intensity, to zero in on 
the most significant range of values.

2.  Apply a variety of color tables to the data, and adjust the gamma of those 
color tables.

3.  Display the logarithm of the data.  I've also found it useful to display the 
Nth root.

Unfortunately, there's no right answer that covers all situations.  It really 
depends on the data.

Bill Thompson


Michael Williams wrote:
> Maren,
> 
> I understand that.  But many of the sample FITS files we've been  
> given have ASCII data in a header, then literally an accompanying  
> "picture"; unless, of course, it's simply a matter of the programs  
> we're using automatically interpreting the "picture".  Is this  
> incorrect?  Our concern is how to properly display the "picture" and  
> what relationship it has to other "picture" formats.
> 
> If it's not a picture, then what is it *exactly*?  Simple plots of  
> data?  How is it to be interpreted?  We've got a TON of data  
> regarding what FITS is supposed to be, but nothing regarding the  
> actual interpreting of data.
> 
> Any suggestions you have would be greatly appreciated.
> 
> Regards,
> Michael
> 
> 
> 
> On Aug 20, 2007, at 5:49 PM, Maren Purves wrote:
> 
> 
>>Michael,
>>
>>it's not graphics, it's data.
>>Well described reducible data.
>>You can't get much physics out of just images.
>>
>>Aloha,
>>Maren
>>
>>gberz3 wrote:
>>
>>>Thanks Maren.  One question I suppose I've just forgotten to ask:  Is
>>>there anything particularly special about the actual graphics content
>>>of a FITS file?  Or is it perhaps simply a glorified TIFF or JPEG of
>>>some sort?
>>>Regards,
>>>Michael
>>>On Aug 4, 11:09 pm, Maren Purves <m.pur... at jach.hawaii.edu> wrote:
>>>
>>>>On Fri, 3 Aug 2007, gberz3 wrote:
>>>>
>>>>>So far, I've really only looked at the CFITSIO items and it's very
>>>>>well documented (really too well) but the function names don't seem
>>>>>very intuitive.  I'm sure they mean a lot more to someone familiar
>>>>>with FITS, but I'm absolutely not.  It's basically like someone in
>>>>>1989 asking you to write a JPEG file manipulation program.  Sure  
>>>>>the
>>>>>information exists, but with 0 familiarity you'll need a lot of  
>>>>>input.
>>>>
>>>>there used to be a file called longnames.h ...
> 
> 
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-- 
William Thompson
NASA Goddard Space Flight Center
Code 671
Greenbelt, MD  20771
USA

301-286-2040
William.T.Thompson.1 at gsfc.nasa.gov