IRAF Image Arrays

Image arrays (e.g. dev$pix) are the standard IRAF data files. They are composed of 3 separate files which are linked together by IRAF:

• *.imh file, stored in the current directory, contains only the header and a pointer to the associated .pix file.
• *.pix file, always stored in the image directory imdir (which the user specifies in the login.cl file), contains the data. These are large files, whose size depends on the size of the data array (e.g., over 1 Mbyte for a 512$\times$512 field).
• ..*.imh file, stored in the current directory. A link used by IRAF to protect the first two files.

By default, *.imh files are stored in the current directory. The associated pixel files are stored in the image directory (imdir) as they are often large. IRAF can only access a *.pix file via the *.imh file which points to it. The two are always treated together by IRAF e.g. if you write *.imh to tape in FITS format, the associated *.pix files are written as well. These files should only be manipulated from inside IRAF to correctly preserve the links, i.e. use imdelete and imcopy and NOT their unix equivalents.

Choices about printer, graphic device, editor, user's `myiraf' directory (identified as home by IRAF), and image directory (identified as imdir by IRAF), are contained in the login.cl file or loginuser.cl and can be edited as required.