![]() ![]() ASCII Table Extension - rows and columns of data in ASCII character format.Image Extension - an N-dimensional array of pixels, as in a primary array.Three standard types of extensions have been included in the FITS Standard since the mid-1990s: A FITS file may have an empty primary array and comprise only extensions. FITS_3 documented support for 16 and 32-bit unsigned integers.Īny number of additional HDUs may follow the primary array these additional HDUs are called FITS extensions. Data types supported in the primary array in FITS_3 are: unsigned 8-bit bytes, 16, 32, and 64-bit signed integers, and 32 and 64-bit single or double precision floating point reals (using the ANSI/IEEE-754 standard, approved by IEEE in 1985). The primary array may be empty or contain an N-dimensional array of pixels, such as a 1-D spectrum, a 2-D image, or a 3-D data cube. A WCS convention for specifying time and relative dimensions in space is in preparation as of early 2013.Ī FITS file consists of one or more Header + Data Units (HDUs), where the first HDU is called the primary HDU, or primary array. The WCS conventions are implemented through an extensive set of reserved keywords and values to be used in headers associated with image arrays. ![]() ![]() WCS conventions also exist to define mappings for a spectral coordinate into a standard frame of reference, allowing spectral shifts due to the Doppler effect and/or cosmic expansion to be accounted for. Version 3 (published in 2012 and distinguished in this format resource as FITS_3) documented several features approved since the previous edition of the full specification: support for 64-bit integers (from an earlier maximum of 32 bits) in images and tables tables with variable-length arrays and adopted new World Coordinate Systems (WCS) conventions to map an element in a data array to standard physical coordinates on the sky. FITS includes many provisions for describing photometric and spatial calibration details, together with image origin metadata.įITS was designed with an eye towards long-term archival use, and the maxim "once FITS, forever FITS" (or "once FITS, always FITS") has guided the IAU to ensure that the format is backwards compatible as new features are added. A dimension of the n-cube may also represent time steps, or indeed be used to represent other data characteristics.įITS is also often used to store non-image data, such as spectra, photon lists, data cubes, or even structured data such as multi-table databases. Astronomy images are often rendered in false color in order to make infra-red and ultra-violet radiation visible. There is no assumption in astronomical analysis or in FITS of a defined colorspace (such as RGB). When FITS is used for straightforward image data, it is often (but not always) in one of two forms: two-dimensional (X, Y) with single values at each point, perhaps some measurement of intensity in a particular spectral band (comparable to grayscale) or three-dimensional (X, Y, color), with the third axis representing different points on a spectral axis, as measured by wavelength, frequency, or some other appropriate scale. For the same reason, in this resource, FITS is categorized primarily as a dataset format, with use for image data as secondary. The substantial use of FITS for data that even astronomers would not class as image data led to consideration to change the full name for the FITS format, but the proposal was rejected. Two-dimensional tables containing rows and columns of data can also be stored in a FITS file. These multi-dimensional arrays may be 1-D spectra, 2-D images or data cubes of three or more dimensions. FITS was designed to facilitate the unambiguous transmission of n-dimensional regularly spaced data arrays, an n-cube. From its beginning, FITS was seen as a transport format for more than a still image intended for printing or viewing in two dimensions. Astronomers view their images as data for analysis rather than simply as pictures to look at. The term "image" in the standard's name is loosely applied and FITS files often contain only non-image data. FITS is a fileįormat designed to store, transmit, and manipulate scientific images and associated data. In 2012, FITS is still in widespread use as a data interchange and archiving format by astronomers. Flexible Image Transport System (FITS), Version 3.0įlexible Image Transport System (FITS) was initially developed by astronomers in the USA and Europe in the late 1970s to serve the interchange of data between observatories and was brought under the auspices of the International Astronomical Union in 1982.
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