08 June 2009

A FITS thumbnailer for Thunar

If you work in Astronomy, you will likely have a lot of fits files lying around. Although the FITS format is absolutely not an image-only format, I would still like to see a preview in my filemanager if there is an image encoded in the file. The standard thumbnailers for Xubuntu don't do this, so here is how to create your own:

create a desktop file that describes, what your thumbnailer does:
/usr/share/thumbnailers/fits-thumbnailer.desktop

[Desktop Entry]
Version=1.0
Encoding=UTF-8
Type=X-Thumbnailer
Name=FITS Thumbnailer
MimeType=image/x-fits;image/fits;application/fits;
X-Thumbnailer-Exec=python /usr/lib/thunar-thumbnailers/fits-thumbnailer.py %i %o %s

create the thumbnailer script under:
/usr/lib/thunar-thumbnailers/fits-thumbnailer.py

    #!/usr/bin/env python
    import pyfits
    import matplotlib.pyplot as plt
    import sys    
    try:
        infile  = sys.argv[1]
        outfile = sys.argv[2]
    except:
        exit(1)    
    try:
        size = sys.argv[3]
    except:
        size = 256    
    hdul = pyfits.open(infile)
    data = None
    # Is the primary HeaderDataUnit an image with data?
    if (hdul[0].header["NAXIS"] != 0):
        data = hdul[0].data
    else:
        # The primary had no data, so we search for the first image!
        for hdu in hdul[1:]:
            if (hdu.header["XTENSION"] == "IMAGE"):
                data = hdu.data
                break
    if data != None:
        plt.imshow(data)
        plt.savefig(outfile, transparent=False, format="png")

regenerate the thumbnailer cache:

    /usr/lib/thunar/thunar-vfs-update-thumbnailers-cache-1

See it in action:

There are actually a lot of cases, where this will not work, it will not take WCS into account and is in general not very sophisticated, but it works for me (TM). For more information about Thunar thumbnailers see:
Customizing Thunar
Additional thunar thumbnailers
Freedesktop thumbnailer spezification
Freedesktop desktop-entry spezification

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