Flexible Image Transport System (FITS) is an

open standard An open standard is a standard that is openly accessible and usable by anyone. It is also a prerequisite to use open license, non-discrimination and extensibility. Typically, anybody can participate in the development. There is no single definition ...

defining a digital

file format A file format is a standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free. Some file formats ...

useful for storage, transmission and processing of data: formatted as multi-dimensional arrays (for example a 2D image), or tables. FITS is the most commonly used digital

astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...

. The FITS standard was designed specifically for astronomical data, and includes provisions such as 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 (4.0) was standardized in 2016. 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

backward compatible Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially i ...

. Image metadata is stored in a human-readable

ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...

header. The information in this header is designed to calculate the byte offset of some information in the subsequent data unit to support direct access to the data cells. Each FITS file consists of one or more headers containing ASCII

card image Card image is a traditional term for a character string, usually 80 characters in length, that was, or could be, contained on a single punched card. IBM cards were 80 characters in length. UNIVAC cards were 90 characters in length. Card image files ...

s 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 A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...

lists, data cubes, or

structured data A data model is an abstract model that organizes elements of data and standardizes how they relate to one another and to the properties of real-world entities. For instance, a data model may specify that the data element representing a car be co ...

such as multi-table

database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases sp ...

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 An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

and

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

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 for example time or 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 In geometry, a coordinate system is a system that uses one or more numbers, or coordinates, to uniquely determine the position of the points or other geometric elements on a manifold such as Euclidean space. The order of the coordinates is sig ...

s that are overlaid on the image itself. Images contain an implicit

Cartesian coordinate system A Cartesian coordinate system (, ) in a plane is a coordinate system that specifies each point uniquely by a pair of numerical coordinates, which are the signed distances to the point from two fixed perpendicular oriented lines, measured in t ...

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 Astronomical coordinate systems are organized arrangements for specifying positions of satellites, planets, stars, galaxies, and other celestial objects relative to physical reference points available to a situated observer (e.g. the true horizo ...

. 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 (sometimes written as Healpix), an acronym for Hierarchical Equal Area isoLatitude Pixelisation of a 2-sphere, is an algorithm for pixelisation of the 2-sphere and the associated class of map projections. The pixelisation algorithm was de ...

spherical projection widely used in observing the

cosmic microwave background radiation In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...

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 database A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relatio ...

Using FITS files

FITS support is available in a variety of programming languages that are used for scientific work, including C,

C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...

, C#, Fortran,

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 ha ...

, IDL,

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...

Julia Julia is usually a feminine given name. It is a Latinate feminine form of the name Julio and Julius. (For further details on etymology, see the Wiktionary entry "Julius".) The given name ''Julia'' had been in use throughout Late Antiquity (e.g ...

LabVIEW Laboratory Virtual Instrument Engineering Workbench (LabVIEW) is a system-design platform and development environment for a visual programming language from National Instruments. The graphical language is named "G"; not to be confused with G-co ...

Mathematica Wolfram Mathematica is a software system with built-in libraries for several areas of technical computing that allow machine learning, statistics, symbolic computation, data manipulation, network analysis, time series analysis, NLP, optimizat ...

MATLAB MATLAB (an abbreviation of "MATrix LABoratory") is a proprietary multi-paradigm programming language and numeric computing environment developed by MathWorks. MATLAB allows matrix manipulations, plotting of functions and data, implementation ...

Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offici ...

Perl Data Language Perl Data Language (abbreviated PDL) is a set of free software array programming extensions to the Perl programming language. PDL extends the data structures built into Perl, to include large multidimensional arrays, and adds functionality to m ...

(PDL),

Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...

, R, and

Tcl TCL or Tcl or TCLs may refer to: Business * TCL Technology, a Chinese consumer electronics and appliance company **TCL Electronics, a subsidiary of TCL Technology * Texas Collegiate League, a collegiate baseball league * Trade Centre Limited ...

. The FITS Support Office at

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

GSFC The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...

maintains a list of libraries and platforms that currently support FITS. Image processing programs such as

ImageJ ImageJ is a Java-based image processing program developed at the National Institutes of Health and the Laboratory for Optical and Computational Instrumentation (LOCI, University of Wisconsin). Its first version, ImageJ 1.x, is developed in the pub ...

GIMP GIMP ( ; GNU Image Manipulation Program) is a free and open-source raster graphics editor used for image manipulation (retouching) and image editing, free-form drawing, transcoding between different image file formats, and more specialized task ...

Photoshop Adobe Photoshop is a raster graphics editor developed and published by Adobe Inc. for Windows and macOS. It was originally created in 1988 by Thomas and John Knoll. Since then, the software has become the industry standard not only in raster ...

Chasys Draw IES Chasys Draw IES (previously called Chasys Draw Artist) is a suite of applications including a layer-based raster graphics editor with adjustment layers, linked layers, timeline and frame-based animation, icon editing, image stacking and comp ...

XnView XnView is an image organizer and general-purpose file manager used for viewing, converting, organizing and editing raster images, as well as general purpose file management. It comes with built-in hex inspection, batch renaming and screen cap ...

and

IrfanView IrfanView () is an image viewer, editor, organiser and converter program for Microsoft Windows. It can also play video and audio files, and has some image creation and painting capabilities. IrfanView is free for non-commercial use; commercial u ...

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 The ESA/ESO/NASA FITS (Flexible Image Transport System) Liberator is a free software program for processing and editing astronomical science data in the FITS format to reproduce images of the universe. Version 3 and later are standalone programs; ...

software is used by imaging scientists at the

European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...

, the

European Southern Observatory The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental organization, intergovernmental research organisation made up of 16 mem ...

and

. 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 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 anal ...

solar-physics-related software tree, the

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 1990s, it also supplied comput ...

AST library in C, and the PyFITS package in Python, now merged into the

Astropy Astropy is a collection of software packages written in the Python programming language and designed for use in astronomy. The software is a single, free, core package for astronomical utilities due to the increasingly widespread usage of Python ...

library.

Current status

The FITS standard version 4.0 was officially approved by the

IAU The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...

FITS Working Group in July 2016.

Notes

References

External links

* , Goddard Support Office
FITS Birthday Announcement
- Historical note from Don Wells on the events leading up to the 'birth' of the FITS format in 1979.

a list of software for reading and writing FITS files for various languages
SAOImage DS9
{{DEFAULTSORT:Fits Astronomical imaging Graphics file formats High dynamic range file formats