| FITS | |
|---|---|
| Filename extension | .fits,.fit,.fts |
| Internet media type | image/fits application/fits[1] |
| Developed by | IAU FITS Working Group[2] |
| Initial release | 1981; 45 years ago (1981) |
| Latest release | 4.0 July 2016; 9 years ago (2016-07) |
| Type of format | image format,structured data |
| Website | fits |
Flexible Image Transport System (FITS) is anopen standard defining a digitalfile format used for storage, transmission and processing of data: formatted as multi-dimensional arrays (for example a 2D image), or tables.[3] FITS is the most commonly used digitalfile format inastronomy. The FITS standard was designed specifically for astronomical data, and includes provisions such as describingphotometric and spatial calibration information, together with image origin metadata.
The FITS format was first standardized in 1981;[4] 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 maximonce FITS, always FITS represents the requirement that developments to the format must bebackward compatible.
Image metadata is stored in a human-readableASCII 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 ASCIIcard images (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 asspectra,photon lists,data cubes, orstructured data such as multi-tabledatabases. A FITS file may contain several extensions, and each of these may contain a data object. For example, it is possible to storex-ray andinfrared exposures in the same file.
The earliest and still most commonly used type of FITS data is an image header/data block.[citation needed] 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 scientificcoordinate systems that are overlaid on the image itself. Images contain an implicitCartesian coordinate system that describes the location of each pixel in the image, but scientific uses usually require working in 'world' coordinates, for example thecelestial 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 differentspherical projections, including, for example, theHEALPix spherical projection widely used in observing thecosmic microwave background radiation.[5]
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 entirerelational databases.
FITS support is available in a variety of programming languages that are used for scientific work, includingC,[6]C++,C#,Fortran,[6]IGOR Pro,IDL,Java,Julia,[7]LabVIEW,Mathematica,MATLAB,Perl,Perl Data Language (PDL),Python,R, andTcl. The FITS Support Office atNASA/GSFC maintains a list of libraries and platforms that currently support FITS.[8]
Image processing programs such asImageJ,GIMP,Photoshop,PhotoLine,Chasys Draw IES,XnView andIrfanView 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. TheFITS Liberator software is used by imaging scientists at theEuropean Space Agency, theEuropean Southern Observatory andNASA.[9] The SAOImage DS9 Astronomical Data Visualization Application[10] is available for many OSs, and handles images and headers.[11]
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 theSolarsoft solar-physics-related software tree, theStarlink Project AST library in C, and the PyFITS package in Python, now merged into theAstropy library.[12]
The FITS standard version 4.0 was officially approved by theIAU FITS Working Group in July 2016.[13][14]
| FITS version | Support level | Release date | Notes |
|---|---|---|---|
| 4.0 | Current standard | July 2016[15] | Final 'language-edited' version formally approved on 13 August 2018[16] |
| 3.0 | Old standard; still supported | July 2008[15] | - |
| 2.1b | Old standard; still supported | December 2005[15] | Added support for 64-bit integer primary arrays and image extensions |
| NOST 100-2.0 | Old standard; still supported | March 1999[15] | - |
| NOST 100-1.0 | Old standard; still supported | June 1993[15] | - |
| Raster | |
|---|---|
| Raw | |
| Vector | |
| Compound | |
| Metadata |
|
