Images and Tables are the two most useful concepts in GILDAS. Practically all data used by GILDAS are stored as Images (or Tables). An Image is a data file containing an array of up to 4 dimensions, and a small but comprehensive header to store the array dimensions, associated coordinates, etc...Tables are just 2-d Images with only the dimensions indicated in the header.
Images are used everywhere in GILDAS. The SIC command monitor directly manipulates Images through the DEFINE IMAGE command. The GREG program is able to display Images as contour plots with overlaid bitmaps. CLASS and CLIC, after working with their own data files, produce Images for further processing and display. And finally, all Tasks use Images for input and output.
Because of this importance of Images, we recommend the GILDAS users to read carefully the corresponding section in the SIC manual. Very efficient use of Images is possible within SIC, but it is also possible to do things a 1000 times more slowly. The ability of SIC to perform mathematics on Images can solve many problems, and avoid many ``on-purpose'' programs.
Images can even be initialized easily from external files of many different formats using the ACCEPT command of SIC, which allows the user to read in a totally flexible way data files to set the content of SIC variables.
Conversion from FITS format to Images is possible using several tools (because of the inherent complexities of the FITS format). Simple FITS files can even be automatically translated into Images.