The IMAGE format as used by some commands in earlier versions of Kappa is a simple HDS structure, comprising a floating-point data array, a character title, and the maximum and minimum data values. It is variant of the original Wright-Giddings IMAGE structure. There are others is use that contain more items. An example structure is shown schematically below using the Hdstrace (SUN/102) notation; see the NDF format.
The DATA_ARRAY may have up to seven dimensions. IMAGE structures are associated with parameters like INPIC and OUTPIC. The TITLE object of new IMAGE structures takes the value of the Parameter OTITLE. DATA_MIN and DATA_MAX are now ignored.
The IMAGE format is not too dissimilar from a primitive NDF with no extensions. Indeed if it did not have DATA_MAX and DATA_MIN it would be a bona fide NDF. Thus applications that handle the IMAGE format can follow the rules of SGP/38 and process it like an NDF. In effect this means that all extensions are propagated to output files, and a quality array is propagated where the processing does not invalidate its values. IMAGE applications also handle most simple NDFs correctly (those where the data array is an array of numbers at the second level of the hierarchical structure). This similarity in formats enables NDF and IMAGE applications to work in co-operation, and so the conversion within Kappa was undertaken piecemeal over several years. Note that the primitive variant is no longer the norm for NDFs, since for example, it does not support origin information.