A Guide To Linux Printing - page 5
Often the raw output of an application is not suitable to be printed. The print spooler can pass the file through a user defined filter which will convert the data to a format that is easier to print. The most common uses of a filter is to convert Postscript input to output that is specific to your printer. A program named Ghostscript is usually used to do the actual conversion. A filter is a shell script that executes a series of commands sending the output back to the print spooler. Several pieces of software are available that contain pre-built filters. Most Linux distributions come with a GUI front end that configures printers. The front end will automatically build an appropriate filter for your printer based on the options you select. In Red Hat Linux the program "printtool" does this task. Users who want more advanced printer filters including the ability to print JPEG or GIF files directly from the command line should look at Magiccap.. Magiccap is a comprehensive filter package that uses Ghostscript and netpbm(image conversion software) to print a variety of graphic formats.