The Flexible Image Transport System (FITS) image extension provides a
convenient means of storing two or more related but not necessarily id
entical multidimensional arrays in a single file. It conforms to the g
uidelines and rules for generalized FITS extensions and is structured
in a manner identical to that of a primary header and data unit; there
by making it simple to interpret and compatible with existing FITS rea
ders. The structure of the image extension and its potential uses are
discussed.