Frequently Asked Questions

  • Flexible Image Transport System.

  • The FITS is a widely used format for storing images and data in Astronomy and Astrophysics, born in the context of radio astronomy in Europe and then adopted by NASA and virtually all scientific institutions in the sector. This format was created in the early 70s to facilitate the exchange of information and images among scientists.
    To resolve this problem some specifications were defined to write data according to an easily readable standard system.
    In 1979, the specifications of what would become the format FITS were widespread. (references to the first article on the FITS)

  • Yes. It's free and you do not need a license.

  • Yes, currently most of the space missions and many astronomical projects using this format for data storage. FITS format is currently one of the most commonly used format in astronomy.

  • FITS format defines a set of rules that require writing the data in a standard format, so you can use it in any kind of operating system.

  • In 1988 IAU (International Astronomical Union), a no profit international association of scientists of the space and astronomical sector has established the IAU FITS Working Group, which handles this format and make it always useful to the needs of modern science with updates and improvements. The IAU FITS Working Group is composed of following regional committees:
    • The European FITS Committee
    • or The Japanese FITS Committee
    • or The American Astronomical Society FITS Committee.
    • or The Astralian/New Zealand/Pacific FITS Committee


  • Yes. In strict accordance with the standards of the IAU scientists try to enrich and improve this format to keep it in step with the needs of science. In July 2008, the IAU FITS Working Group has officially approved the new version 3.0 of the format with some new features.

  • Yes. The golden rule of this format is "once FITS, always FITS". Once the data has been written using this format must always be read in the following years despite changes in the format. Compared to the original version over the years we have been added to new possibilities, new features, but always maintaining full compatibility with older versions.

  • FITS
    In few words a FITS file is composed by two distinct parts, which can be repeated several times: the first part (header) is formed by easily viewable ASCII text elements with data description and other information, while in the second part there are the data in binary format.

    Most information in the HDU are are in this form:

    KEYWORD = Value
    Ex: NAXIS = 2
  • The Space Color

  • The FITS format is fully documented and all information are freely available in a lot of places.You can found official reference documents at:

  • FITS is not only a graphic format (like TIFF for example) but a way to save various data. For more information about this argoment see this document written by Stefano Allegrezza presentad to EWASS 2012. In the document by the way they are compared critically various formats.

  • Currently graphics programs that can manage FITS filef like GIMP or Photoshop allow conversion to / from FITS only of the image without any other information because they does not have the ability to read other keywords in addition to those fundamental related to the image like NAXIS and BITPIX.
    We hope that in the future graphic programs will be able to manage FITS files directly or using appropriate plugins. You can convert a FITS image in another format using a programming language.

  • In scientific environment, there are some programs to manage this format, but most of them are very specialized for astronomy. There are also libraries for different languages, such as C ++, FORTRAN and Java, which let you use files with this extension.
    A good graphics program that allows you to read, write and manipulate FITS files is GIMP, a very powerful and free editing program distributed under open source license.
    Its features are comparable with the ADOBE PHOTOSHOP.
    To manage FITS file in ADOBE Phototshop you have to use a plug-in.

    Another interesting tool is The ESA/ESO/NASA FITS Liberator 3, a free software program for processing and editing astronomical science data in the FITS format. Version 3 and later are standalone programs but earlier versions were plugins for Adobe Photoshop.

  • Standard FITS does not provide a data compression. However, several useful routines in programming language or executable from the UNIX command line allowing to compress the data saved in FITS These programs are similar to standard gzip and gunzip programs, but they are specifically optimized for images in FITS format and offer a wider choice of compression options. One of the most common is fpack/funpack, freely available at this address:
    that besides having a high ability to compress data has many other interesting features, such as the fact that the compressed image is in itself a FITS file. Also the header with the keywords can be not-compressed for quick access and search for information in the keywords.

  • FVerify is a free utility to check the compliant of the file to the FITS standard.

  • Example N.1 - BASIC Primary Header Unit
     /Mandatory keywords:
    SIMPLE = T/This file is compliant to FITS standard
    BITPIX = -32/ Data are Real * 4
    NAXIS = 2/ 2-D Matrix
    NAXIS1 = 512/ X axis is 512 pixel
    NAXIS2 = 512/ Y axis is 512 pixel
    END/ End of FITS header

    This information can be read easily and show that file contains a 512x512 matrix elements where each element is a 32 bit real number.

    Example N.2 - Astronomic Primary Header Unit
    SIMPLE = T/ This file is compliant to FITS standard
    BITPIX = 16/
    NAXIS = 4/
    NAXIS1 = 1024/
    NAXIS2 = 1034/
    NAXIS3 = 3/
    NAXIS4 = 1/
    EXTEND = T/Tables following main image
    BLOCKED = T/Tape may be blocked
    OBJECT = 'C0000P40'
    DATE-OBS= '15/12/93'
    DATE-MAP= '03/04/98'
    BSCALE = 9.99999974738E-05/REAL = TAPE * BSCALE + BZERO
    BZERO = 0.00000000000E+00/
    BUNIT = 'JY/BEAM '
    EPOCH = 2.000000000E+03/EPOCH OF RA DEC
    OBSDEC = 4.00000000000E+01/ANTENNA POINTING DEC
    DATAMAX = 1.246536493E+00/MAX PIXEL VALUE
    DATAMIN = -1.483317930E-02/MIN PIXEL VALUE
    CTYPE1 = 'RA---SIN'
    CRVAL1 = 0.00000000000E+00/
    CDELT1 = -4.166666884E-03/
    CRPIX1 = 5.120000000E+02/
    CROTA1 = 0.000000000E+00/
    CTYPE2 = 'DEC--SIN'
    CRVAL2 = 4.00000000000E+01/
    CDELT2 = 4.166666884E-03/
    CRPIX2 = 5.130000000E+02/
    CROTA2 = 0.000000000E+00/
    CTYPE3 = 'STOKES '
    CRVAL3 = 1.00000000000E+00/
    CDELT3 = 1.000000000E+00/
    CRPIX3 = 1.000000000E+00/
    CROTA3 = 0.000000000E+00/
    CTYPE4 = 'FREQ '
    CRVAL4 = 1.40000000000E+09/
    CDELT4 = 1.000000000E+08/
    CRPIX4 = 1.000000000E+00/
    CROTA4 = 0.000000000E+00/
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