FITS
Encyclopedia
Flexible Image Transport System (FITS) is a digital file format
used to store, transmit, and manipulate scientific and other images. FITS is the most commonly used digital file format
in astronomy
. Unlike many image formats, FITS is designed specifically for scientific data and hence includes many provisions for describing photometric
and spatial calibration information, together with image origin metadata.
The FITS format was first standardized in 1981; it has evolved gradually since then, and the most recent version (3.0) was standardized in 2008. FITS was designed with an eye towards long-term archival storage, and the maxim once FITS, always FITS represents the requirement that developments to the format must be backwards compatible.
A major feature of the FITS format is that image metadata is stored in a human-readable ASCII
header, so that an interested user can examine the headers to investigate a file of unknown provenance. Each FITS file consists of one or more headers containing ASCII card image
s (80 character fixed-length strings) that carry keyword/value pairs, interleaved between data blocks. The keyword/value pairs provide information such as size, origin, coordinates, binary data format, free-form comments, history of the data, and anything else the creator desires: while many keywords are reserved for FITS use, the standard allows arbitrary use of the rest of the name-space.
FITS is also often used to store non-image data, such as spectra
, photon
lists, data cube
s, or even structured data such as multi-table database
s. A FITS file may contain several extensions, and each of these may contain a data object. For example, it is possible to store x-ray
and infrared
exposures in the same file.
FITS image headers can contain information about one or more scientific coordinate system
s that are overlaid on the image itself. Images contain an implicit Cartesian coordinate system
that describes the location of each pixel in the image, but scientific uses usually require working in 'world' coordinates, for example the celestial coordinate system
. As FITS has been generalized from its original form, the world coordinate system (WCS) specifications have become more and more sophisticated: early FITS images allowed a simple scaling factor to represent the size of the pixels; but recent versions of the standard permit multiple nonlinear coordinate systems, representing arbitrary distortions of the image. The WCS standard includes many different spherical projections, including, for example, the HEALPix
spherical projection widely used in observing the cosmic microwave background radiation
.
s.
, C++
, C#, Fortran
, IGOR Pro
, IDL, Java
, LabVIEW
, Mathematica
, MatLab
, Perl
, PDL
, Python
, R
, and Tcl
. The FITS Support Office at NASA
/GSFC
maintains a list of libraries and platforms that currently support FITS.
Image processing programs such as GIMP
, Photoshop, XnView
and IrfanView
can generally read simple FITS images, but frequently cannot interpret more complex tables and databases. Scientific teams frequently write their own code to interact with their FITS data, using the tools available in their language of choice. The FITS Liberator
software is used by imaging scientists at the European Space Agency
, the European Southern Observatory
and NASA
. The SAOImage DS9 Astronomical Data Visualization Application is available for many OSs, and handles images and headers.
Many scientific computing environments make use of the coordinate system data in the FITS header to display, compare, rectify, or otherwise manipulate FITS images. Examples are the coordinate transform library included with PDL, the PLOT MAP library in the Solarsoft
solar-physics-related software tree, the Starlink Project
AST library in C, and the PyFITS package in Python.
FITS Working Group in July 2008.
File format
A file format is a particular way that information is encoded for storage in a computer file.Since a disk drive, or indeed any computer storage, can store only bits, the computer must have some way of converting information to 0s and 1s and vice-versa. There are different kinds of formats for...
used to store, transmit, and manipulate scientific and other images. FITS is the most commonly used digital file format
File format
A file format is a particular way that information is encoded for storage in a computer file.Since a disk drive, or indeed any computer storage, can store only bits, the computer must have some way of converting information to 0s and 1s and vice-versa. There are different kinds of formats for...
in astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
. Unlike many image formats, FITS is designed specifically for scientific data and hence includes many provisions for describing photometric
Photometry (optics)
Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy in terms of absolute power; rather, in photometry, the radiant power at each wavelength is weighted by...
and spatial calibration information, together with image origin metadata.
The FITS format was first standardized in 1981; it has evolved gradually since then, and the most recent version (3.0) was standardized in 2008. FITS was designed with an eye towards long-term archival storage, and the maxim once FITS, always FITS represents the requirement that developments to the format must be backwards compatible.
A major feature of the FITS format is that image metadata is stored in a human-readable ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
header, so that an interested user can examine the headers to investigate a file of unknown provenance. Each FITS file consists of one or more headers containing ASCII card image
Card image
A card image is an archaic term for an ASCII string, usually 80 bytes in length. "Card image" refers to a punched card. IBM cards were 80 characters in length, UNIVAC cards were 90 characters. A single card typically held a single line of text, for example a line of FORTRAN code...
s (80 character fixed-length strings) that carry keyword/value pairs, interleaved between data blocks. The keyword/value pairs provide information such as size, origin, coordinates, binary data format, free-form comments, history of the data, and anything else the creator desires: while many keywords are reserved for FITS use, the standard allows arbitrary use of the rest of the name-space.
FITS is also often used to store non-image data, such as spectra
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
, photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
lists, data cube
Data cube
In computer programming contexts, a data cube is a three- dimensional array of values, commonly used to describe a time series of image data...
s, or even structured data such as multi-table database
Database
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
s. A FITS file may contain several extensions, and each of these may contain a data object. For example, it is possible to store x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
and infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
exposures in the same file.
Images
The earliest and still most commonly used type of FITS data is an image header/data block. The term 'image' is somewhat loosely applied, as the format supports data arrays of arbitrary dimension—normal image data are usually 2-D or 3-D (with the third dimension representing the color plane). The data themselves may be in one of several integer and floating-point formats, specified in the header.FITS image headers can contain information about one or more scientific coordinate system
Coordinate system
In geometry, a coordinate system is a system which uses one or more numbers, or coordinates, to uniquely determine the position of a point or other geometric element. The order of the coordinates is significant and they are sometimes identified by their position in an ordered tuple and sometimes by...
s that are overlaid on the image itself. Images contain an implicit Cartesian coordinate system
Cartesian coordinate system
A Cartesian coordinate system specifies each point uniquely in a plane by a pair of numerical coordinates, which are the signed distances from the point to two fixed perpendicular directed lines, measured in the same unit of length...
that describes the location of each pixel in the image, but scientific uses usually require working in 'world' coordinates, for example the celestial coordinate system
Celestial coordinate system
In astronomy, a celestial coordinate system is a coordinate system for mapping positions on the celestial sphere.There are different celestial coordinate systems each using a system of spherical coordinates projected on the celestial sphere, in analogy to the geographic coordinate system used on...
. As FITS has been generalized from its original form, the world coordinate system (WCS) specifications have become more and more sophisticated: early FITS images allowed a simple scaling factor to represent the size of the pixels; but recent versions of the standard permit multiple nonlinear coordinate systems, representing arbitrary distortions of the image. The WCS standard includes many different spherical projections, including, for example, the HEALPix
HEALPix
HEALPix , an acronym for Hierarchical Equal Area isoLatitude Pixelisation of a 2-sphere, can refer to either an algorithm for pixelisation of the 2-sphere, an associated software package, or an associated class of map projections.The HEALPix projection is a general class of spherical projections,...
spherical projection widely used in observing the cosmic microwave background radiation
Cosmic microwave background radiation
In cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....
.
Tables
FITS also supports tabular data with named columns and multidimensional rows. Both binary and ASCII table formats have been specified. The data in each column of the table can be in a different format from the others. Together with the ability to string multiple header/data blocks together, this allows FITS files to represent entire relational databaseRelational database
A relational database is a database that conforms to relational model theory. The software used in a relational database is called a relational database management system . Colloquial use of the term "relational database" may refer to the RDBMS software, or the relational database itself...
s.
Using FITS files
FITS support is available in a variety of programming languages that are used for scientific work, including CC (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
, C++
C++
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
, C#, Fortran
Fortran
Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...
, IGOR Pro
IGOR Pro
IGOR Pro is a scientific data analysis software, numerical computing environment and programming language that runs on Windows or Mac operating systems. It is developed by WaveMetrics Inc., and was originally aimed at time series analysis, but has since then evolved and covers other applications...
, IDL, Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
, LabVIEW
LabVIEW
LabVIEW is a system design platform and development environment for a visual programming language from National Instruments. LabVIEW provides engineers and scientists with the tools needed to create and deploy measurement and control systems.The graphical language is named "G"...
, Mathematica
Mathematica
Mathematica is a computational software program used in scientific, engineering, and mathematical fields and other areas of technical computing...
, MatLab
MATLAB
MATLAB is a numerical computing environment and fourth-generation programming language. Developed by MathWorks, MATLAB allows matrix manipulations, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs written in other languages,...
, Perl
Perl
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...
, PDL
Perl Data Language
PDL is a set of array programming extensions to the Perl programming language.PDL is an extension to Perl v5, intended for scientific and other data intensive programming tasks...
, Python
Python (programming language)
Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Python claims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive...
, R
R (programming language)
R is a programming language and software environment for statistical computing and graphics. The R language is widely used among statisticians for developing statistical software, and R is widely used for statistical software development and data analysis....
, and Tcl
Tcl
Tcl is a scripting language created by John Ousterhout. Originally "born out of frustration", according to the author, with programmers devising their own languages intended to be embedded into applications, Tcl gained acceptance on its own...
. The FITS Support Office at NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
/GSFC
Goddard Space Flight Center
The Goddard Space Flight Center is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately northeast of Washington, D.C. in Greenbelt, Maryland, USA. GSFC,...
maintains a list of libraries and platforms that currently support FITS.
GIMP
GIMP is a free software raster graphics editor. It is primarily employed as an image retouching and editing tool and is freely available in versions tailored for most popular operating systems including Microsoft Windows, Apple Mac OS X, and Linux.In addition to detailed image retouching and...
, Photoshop, XnView
XnView
XnView is a cross-platform image viewer used for viewing, converting, organising and editing graphical & video files. It is free of charge for private, educational and non-profit organisations...
and IrfanView
IrfanView
IrfanView is a freeware/shareware image viewer for Microsoft Windows that can view, edit, and convert image files and play video/audio files. It is noted for its small size, speed, ease of use, and ability to handle a wide variety of graphic file formats, and has some image creation and painting...
can generally read simple FITS images, but frequently cannot interpret more complex tables and databases. Scientific teams frequently write their own code to interact with their FITS data, using the tools available in their language of choice. The FITS Liberator
FITS Liberator
The ESA/ESO/NASA Photoshop FITS Liberator is a free plugin for Adobe Photoshop, which makes it possible to process and edit astronomical science data in the FITS format to produce stunning images of the universe....
software is used by imaging scientists at the European Space Agency
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
, the European Southern Observatory
European Southern Observatory
The European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
and NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
. The SAOImage DS9 Astronomical Data Visualization Application is available for many OSs, and handles images and headers.
Many scientific computing environments make use of the coordinate system data in the FITS header to display, compare, rectify, or otherwise manipulate FITS images. Examples are the coordinate transform library included with PDL, the PLOT MAP library in the Solarsoft
Solarsoft
Solarsoft is a collaborative software development system created at Lockheed-Martin to support solar data analysis and spacecraft operation activities. It is widely recognized in the solar physics community as having revolutionized solar data analysis starting in the early 1990s...
solar-physics-related software tree, the Starlink Project
Starlink Project
The Starlink Project, referred to by users as Starlink and by developers as simply The Project, was a UK astronomical computing project which supplied general-purpose data reduction software. Until the late nineties, it also supplied computing hardware and system administration personnel to UK...
AST library in C, and the PyFITS package in Python.
Current status
The FITS standard version 3.0 was officially approved by the IAUIAU
IAU may refer to:*International Astronomical Union*International American University*International American University College of Medicine*International Association of Universities*International Association of Ultrarunners...
FITS Working Group in July 2008.
Release history
| Meaning | |
|---|---|
| Red | Old Standard/Draft; not supported |
| Yellow | Old Standard; still supported |
| Green | Current Standard |
| Blue | Future Draft |
| FITS Version | Release Date | Notes |
|---|---|---|
| 3.0 | July 2008 | - |
| 2.1b | December 2005 | Added support for 64-bit integer primary arrays and image extensions |
| NOST 100-2.0 | March 1999 | - |
| NOST 100-1.0 | June 1993 | - |
See also
- FITS LiberatorFITS LiberatorThe ESA/ESO/NASA Photoshop FITS Liberator is a free plugin for Adobe Photoshop, which makes it possible to process and edit astronomical science data in the FITS format to produce stunning images of the universe....
- Hierarchical Data FormatHierarchical Data FormatHierarchical Data Format is the name of a set of file formats and libraries designed to store and organize large amounts of numerical data...
(HDF) - Common Data FormatCommon Data FormatCommon Data Format is a library and toolkit that has been developed by NASA. The software is an interface for the storage and manipulation of multi-dimensional data sets.-See also:* CGNS * EAS3...
(CDF) - NetCDFNetCDFNetCDF is a set of software libraries and self-describing, machine-independent data formats that support the creation, access, and sharing of array-oriented scientific data. The project homepage is hosted by the Unidata program at the University Corporation for Atmospheric Research...
External links
- Goddard FITS Support Office
- FITS Birthday Announcement - Historical note from Don Wells on the events leading up to the 'birth' of the FITS format in 1979.
- FITS I/O Libraries, a list of software for reading and writing FITS files for various languages