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

[Maren Purves]

Michael,

as you asked me explicitly: I have very little to add to what Bill
(thanks, Bill) wrote.

Maybe a bit more concise: images in GIFs and JPEGs are made to be
looked at by people. You generally can't get much quantitative science
out of them. FITS files are (or at least should be) fully described,
so that when processed correctly you can derive science from them.

(yes, you could measure e.g. lines out of a spectrum from an image,
but it's much easier if you have the underlying numbers, and a lot
of science has been done with Palomar Observatory Sky Survey prints,
but usually by digitizing them).

Aloha,
Maren

William Thompson wrote:
> 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.