fitsinfo

Information about FITS file

Syntax

info = fitsinfo(filename)

Description

info = fitsinfo(filename) returns the structure, info, with fields that contain information about the contents of a Flexible Image Transport System (FITS) file. filename is a character vector or string scalar that specifies the name of the FITS file.

The info structure contains the following fields, listed in the order they appear in the structure. In addition, the info structure can also contain information about any number of optional file components, called extensions in FITS terminology. For more information, see FITS File Extensions.

Field Name	Description	Return Type
`Filename`	Name of the file	Character vector
`FileModDate`	File modification date	Character vector
`FileSize`	Size of the file in bytes	`double`
`Contents`	List of extensions in the file in the order that they occur	Cell array of character vectors
`PrimaryData`	Information about the primary data in the FITS file	Structure array

Primary Data

The PrimaryData field is a structure that describes the primary data in the file. The following table lists the fields in the order they appear in the structure.

Field Name	Description	Return Type
`DataType`	Precision of the data	Character vector
`Size`	Size of each dimension. The number of rows corresponds to the value of the `NAXIS2` keyword, while the number of columns corresponds to the value of the `NAXIS1` keyword. Any further dimensions correspond to `NAXIS3`, `NAXIS4`, and so on.	`double` array
`DataSize`	Size of the primary data in bytes	`double`
`MissingDataValue`	Value used to represent undefined data	`double`
`Intercept`	Value, used with `Slope`, to calculate actual pixel values from the array pixel values, using the equation: `actual_value = Slope*array_value + Intercept`	`double`
`Slope`	Value, used with `Intercept`, to calculate actual pixel values from the array pixel values, using the equation: `actual_value = Slope*array_value + Intercept`	`double`
`Offset`	Number of bytes from beginning of the file to the location of the first data value	`double`
`Keywords`	An `n`-by-3 cell array, where `n` is the number of keywords, containing keywords, values, and comments of the header in each column	Cell array of character vectors

FITS File Extensions

A FITS file can also include optional extensions. If the file contains any of these extensions, the info structure can contain these additional fields.

AsciiTable — Numeric information in tabular format, stored as ASCII characters
BinaryTable — Numeric information in tabular format, stored in binary representation
Image — A multidimensional array of pixels
Unknown — Nonstandard extension

`AsciiTable` Extension

The AsciiTable structure contains the following fields, listed in the order they appear in the structure.

Field Name	Description	Return Type
`Rows`	Number of rows in the table	`double`
`RowSize`	Number of characters in each row	`double`
`NFields`	Number of fields in each row	`double` array
`FieldFormat`	A 1-by-`NFields` cell containing formats in which each field is encoded. The formats are FORTRAN-77 format codes.	Cell array of character vectors
`FieldPrecision`	A 1-by-`NFields` cell containing precision of the data in each field	Cell array of character vectors
`FieldWidth`	A 1-by-`NFields` array containing the number of characters in each field	`double` array
`FieldPos`	A 1-by-`NFields` array of numbers representing the starting column for each field	`double` array
`DataSize`	Size of the data in the table in bytes	`double`
`MissingDataValue`	A 1-by-`NFields` array of numbers used to represent undefined data in each field	Cell array of character vectors
`Intercept`	A 1-by-`NFields` array of numbers used along with `Slope` to calculate actual data values from the array data values using the equation: `actual_value = Slope*array_value+Intercept`	`double` array
`Slope`	A 1-by-`NFields` array of numbers used with `Intercept` to calculate true data values from the array data values using the equation: `actual_value = Slope*array_value+Intercept`	`double` array
`Offset`	Number of bytes from beginning of the file to the location of the first data value in the table	`double`
`Keywords`	An `n`-by-3 cell array, where `n` is the number of keywords, containing all the keywords, values, and comments in the ASCII table header	Cell array of character vectors

`BinaryTable` Extension

The BinaryTable structure contains the following fields, listed in the order they appear in the structure.

Field Name	Description	Return Type
`Rows`	Number of rows in the table	`double`
`RowSize`	Number of bytes in each row	`double`
`NFields`	Number of fields in each row	`double`
`FieldFormat`	A 1-by-`NFields` cell array containing the data type of the data in each field. The data type is represented by a FITS binary table format code.	Cell array of character vectors
`FieldPrecision`	A 1-by-`NFields` cell containing precision of the data in each field	Cell array of character vectors
`FieldSize`	A 1-by-`NFields` array, where each element contains the number of values in the Nth field	`double` array
`DataSize`	Size of the data in the Binary Table, in bytes. Includes any data past the main table.	`double`
`MissingDataValue`	An 1-by-`NFields` array of numbers used to represent undefined data in each field	Cell array of `double`
`Intercept`	A 1-by-`NFields` array of numbers used along with Slope to calculate actual data values from the array data values using the equation: `actual_value = slope*array_value+Intercept`	`double` array
`Slope`	A 1-by-`NFields` array of numbers used with Intercept to calculate true data values from the array data values using the equation: `actual_value = Slope*array_value+Intercept`	`double` array
`Offset`	Number of bytes from beginning of the file to the location of the first data value	`double`
`ExtensionSize`	Size of any data past the main table, in bytes	`double`
`ExtensionOffset`	Number of bytes from the beginning of the file to any data past the main table	`double`
`Keywords`	An `n`-by-3 cell array, where `n` is the number of keywords, containing all the keywords, values, and comments in the Binary Table header	Cell array of character vectors

`Image` Extension

The Image structure contains the following fields, listed in the order they appear in the structure.

Field Name	Description	Return Type
`DataType`	Precision of the data	Character vector
`Size`	Size of each dimension. The number of rows corresponds to the value of the `NAXIS2` keyword, while the number of columns corresponds to the value of the `NAXIS1` keyword. Any further dimensions correspond to `NAXIS3`, `NAXIS4`, and so on.	`double` array
`DataSize`	Size of the data in the Image extension in bytes	`double`
`Offset`	Number of bytes from the beginning of the file to the first data value	`double`
`MissingDataValue`	Value used to represent undefined data	`double`
`Intercept`	Value, used with `Slope`, to calculate actual pixel values from the array pixel values, using the equation: `actual_value = Slope*array_value+Intercept`	`double`
`Slope`	Value, used with `Intercept`, to calculate actual pixel values from the array pixel values, using the equation: `actual_value = Slope*array_value + Intercept`	`double`
`Keywords`	An `n`-by-3 cell array, where `n` is the number of keywords, containing all the keywords, values, and comments in the Image header	Cell array of character vectors

`Unknown` Structure

The Unknown structure contains the following fields, listed in the order they appear in the structure.

Field Name	Description	Return Type
`DataType`	Precision of the data	Character vector
`Size`	Sizes of each dimension	`double` array
`DataSize`	Size of the data in nonstandard extensions, in bytes	`double`
`Offset`	Number of bytes from beginning of the file to the first data value	`double`
`MissingDataValue`	Representation of undefined data	`double`
`Intercept`	Value, used with `Slope`, to calculate actual data values from the array data values, using the equation: `actual_value = Slope*array_value+Intercept`	`double`
`Slope`	Value, used with `Intercept`, to calculate actual data values from the array data values, using the equation: `actual_value = Slope*array_value+Intercept`	`double`
`Keywords`	An `n`-by-3 cell array, where `n` is the number of keywords, containing all the keywords, values, and comments in the extension header	Cell array of character vectors

Examples

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Get Information About FITS File

Open Live Script

Use fitsinfo to obtain information about the FITS file tst0012.fits. The returned structure contains Filename, FileModDate, FileSize, Contents, and PrimaryData. In addition to its primary data, the file also contains an example of the extensions BinaryTable, Unknown, Image, and AsciiTable.

S = fitsinfo("tst0012.fits");

View the PrimaryData field.

S.PrimaryData

ans = struct with fields:
            DataType: 'single'
                Size: [109 102]
            DataSize: 44472
    MissingDataValue: []
           Intercept: 0
               Slope: 1
              Offset: 2880
            Keywords: {25×3 cell}

The PrimaryData field describes the data in the file. For example, the Size field indicates the data is a 109-by-102 matrix.

View the AsciiTable field.

S.AsciiTable

ans = struct with fields:
                Rows: 53
             RowSize: 59
             NFields: 8
         FieldFormat: {'A9'  'F6.2'  'I3'  'E10.4'  'D20.15'  'A5'  'A1'  'I4'}
      FieldPrecision: {'Char'  'Single'  'Integer'  'Single'  'Double'  'Char'  'Char'  'Integer'}
          FieldWidth: [9 6.2000 3 10.4000 20.1500 5 1 4]
            FieldPos: [1 11 18 22 33 54 54 55]
            DataSize: 3127
    MissingDataValue: {'*'  '---.--'  '  *'  []  '*'  '*'  '*'  ''}
           Intercept: [0 0 -70.2000 0 0 0 0 0]
               Slope: [1 1 2.1000 1 1 1 1 1]
              Offset: 103680
            Keywords: {65×3 cell}

The AsciiTable field describes the AsciiTable extension. For example, using the FieldWidth and FieldPos fields you can determine the length and location of each field within a row.

Extended Capabilities

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Thread-Based Environment
Run code in the background using MATLAB® `backgroundPool` or accelerate code with Parallel Computing Toolbox™ `ThreadPool`. (since R2026a)

The fitsinfo function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced before R2006a

expand all

R2026a: Use function in thread-based environments

You can use this function in thread-based environments.

fitsinfo

Syntax

Description

Primary Data

FITS File Extensions

`AsciiTable` Extension

`BinaryTable` Extension

`Image` Extension

`Unknown` Structure

Examples

Get Information About FITS File

Extended Capabilities

Thread-Based Environment
Run code in the background using MATLAB® `backgroundPool` or accelerate code with Parallel Computing Toolbox™ `ThreadPool`. (since R2026a)

Version History

R2026a: Use function in thread-based environments

See Also

Functions

Topics

External Websites

fitsinfo

Syntax

Description

Primary Data

FITS File Extensions

AsciiTable Extension

BinaryTable Extension

Image Extension

Unknown Structure

Examples

Get Information About FITS File

Extended Capabilities

Thread-Based Environment Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool. (since R2026a)

Version History

R2026a: Use function in thread-based environments

See Also

Functions

Topics

External Websites

`AsciiTable` Extension

`BinaryTable` Extension

`Image` Extension

`Unknown` Structure

Thread-Based Environment
Run code in the background using MATLAB® `backgroundPool` or accelerate code with Parallel Computing Toolbox™ `ThreadPool`. (since R2026a)