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Section 7

Standard Extensions

A standard extension is a conforming extension whose organization and content are

completely specified in this standard. The specifications for the 3 currently defined

standard extensions, namely,

1. 'IMAGE' extensions,

2. 'TABLE' ASCII table extensions, and

3. 'BINTABLE' binary table extensions

are given in the following sections. A list of other conforming extensions is given in

Appendix F

7.1

Image Extension

The FITS image extension is nearly identical in structure to the the primary HDU and

is used to store an array of data. Multiple image extensions can be used to store any

number of arrays in a single FITS file. The first keyword in an image extension shall

be XTENSION=u'IMAGEuuu

'.

7.1.1

Mandatory Keywords

The XTENSION keyword is required to be the first keyword of all image extensions. The

keyword records in the header of an image extension must use the keywords defined in

Table 7.1 in the order specified. No other keywords may intervene between the XTENSION

and GCOUNT keywords.

XTENSION Keyword

The value field shall contain the character string 'IMAGEuuu'.

FITS Standard