National Aeronautics and Space Administration

FITSIO is a machine-independent subroutine interface for reading or writing data files in FITS (Flexible Image Transport System) format. This package was written to provide a powerful yet simple interface for accessing FITS files that insulates the programmer from having to deal directly with the complicated internal details of the FITS file.

FITSIO supports all the common types of FITS files, including Primary Arrays, Image extensions, and ASCII and Binary table extensions. Subroutines are provided to perform various operations on FITS files, such as opening and closing files; reading, writing, modifying or deleting the values of header keywords; and reading or writing any element of the associated data array or table. The FITSIO package also contains extensive error checking to help verify that a given file has a valid FITS format.

FITSIO was originally written in Fortran-77 starting in 1991, then an ANSI-C version (CFITSIO) was released in 1996. Fortran-callable wrappers were added to CFITSIO in 1998 which effectively replace the older FITSIO library. These Fortran-callable wrappers in CFITSIO have exactly the same calling sequence as the original subroutines in FITSIO library and are faster and provide new functionality (like being able to read compressed FITS files).