Add support of FITS file format

[vladtcvs]

Setup (please complete the following information):

• Geeqie version [geeqie --version]: Geeqie 2.4 GTK3

Describe your feature request FITS file format is often used in astrophotography and other scientific cases, and adding support to view FITS format would be great

[vladtcvs]

Example image M_92_Light_R_001.fits.gz

[caclark]

@vladtcvs I have created some code to display .fits files - 2D only.

The intensity range for a pixbuf is 0 to 255. The range in your sample image is 0 to 450, with most of the data below 40.00

After the rescaling is made to show in a pixbuf, the image is just black.

How does other software cope with this extended range? I see that QFitsView has a log scale option.

[vladtcvs]

kstars has viewer of FITS, it stretches values that lowest value is a black and highest - is a white.

[vladtcvs]

Also there is tool called fv, it does the same

[vladtcvs]

I see that QFitsView has a log scale option.

Yes, software which works with FITS usually have possibility to adjust gamma (On the screenshot above it's a "Midtones" slider)

[caclark]

@vladtcvs

I doubt that this is adequate.

Please re-open this issue if you have comments.

Edited to add: Ignore the next sentence. There is a problem generating the AppImages. [If you do not wish to compile from sources, the AppImages let you make a quick check]