However, the rich structure of an HDS file requires that Asterix create further FITS image extensions to store some (but not all) of the information that is normally included within an SDF file.
These extra image extension are normally,
VARIANCE - The errors associated with the data. Stored with the same dimensions and type as the data.
QUALITY - The various quality flags associated with the data. Stored as a byte array with the same dimension as the data.
GCB - (Grapics Control Block) - stores information on the various plot styles, titles, labels, scalling, contouring, &c. used when displaying the data. Stored as 1-D array of bytes.