18.8 Network PostScript RIP

This section discusses the use of CUPS filters on the server ” configuration where clients make use of a PostScript driver with CUPS-PPDs.

PPDs can control all print device options. They are usually provided by the manufacturer, if you own a PostScript printer, that is. PPD files (PostScript Printer Descriptions) are always a component of PostScript printer drivers on MS Windows or Apple Mac OS systems. They are ASCII files containing user -selectable print options, mapped to appropriate PostScript, PCL or PJL commands for the target printer. Printer driver GUI dialogs translate these options " on-the-fly " into buttons and drop-down lists for the user to select.

CUPS can load, without any conversions, the PPD file from any Windows (NT is recommended) PostScript driver and handle the options. There is a Web browser interface to the print options (select http://localhost:631/printers/ and click on one Configure Printer button to see it), or a command line interface (see man lpoptions or see if you have lphelp on your system). There are also some different GUI frontends on Linux/UNIX, which can present PPD options to users. PPD options are normally meant to be evaluated by the PostScript RIP on the real PostScript printer.

18.8.1 PPDs for Non-PS Printers on UNIX

CUPS does not limit itself to " real " PostScript printers in its usage of PPDs. The CUPS developers have extended the scope of the PPD concept to also describe available device and driver options for non-PostScript printers through CUPS-PPDs.

This is logical, as CUPS includes a fully featured PostScript interpreter (RIP). This RIP is based on Ghostscript. It can process all received PostScript (and additionally many other file formats) from clients. All CUPS-PPDs geared to non-PostScript printers contain an additional line, starting with the keyword *cupsFilter . This line tells the CUPS print system which printer-specific filter to use for the interpretation of the supplied PostScript. Thus CUPS lets all its printers appear as PostScript devices to its clients, because it can act as a PostScript RIP for those printers, processing the received PostScript code into a proper raster print format.

18.8.2 PPDs for Non-PS Printers on Windows

CUPS-PPDs can also be used on Windows-Clients, on top of a " core " PostScript driver (now recommended is the "CUPS PostScript Driver for WindowsNT/200x/XP"; you can also use the Adobe one, with limitations). This feature enables CUPS to do a few tricks no other spooler can do:

• Act as a networked PostScript RIP (Raster Image Processor), handling printfiles from all client platforms in a uniform way.

• Act as a central accounting and billing server, since all files are passed through the pstops filter and are, therefore, logged in the CUPS page_log file. Note: this cannot happen with " raw " print jobs, which always remain unfiltered per definition.

• Enable clients to consolidate on a single PostScript driver, even for many different target printers.

Using CUPS PPDs on Windows clients enables these to control all print job settings just as a UNIX client can do.