pstoraster is at the core of the CUPS filtering system. It is responsible for the first stage of the rasterization process. Its input is of MIME type application/vnd.cups-postscript; its output is application/vnd.cups-raster. This output format is not yet meant to be printable. Its aim is to serve as a general-purpose input format for more specialized raster drivers that are able to generate device-specific printer data. This is shown in the PostScript to Intermediate Raster Format diagram.

Figure21.6.PostScript to Intermediate Raster Format.

CUPS raster is a generic raster format with powerful features. It is able to include per-page information, color profiles, and more, to be used by the downstream raster drivers. Its MIME type is registered with IANA and its specification is, of course, completely open. It is designed to make it quite easy and inexpensive for manufacturers to develop Linux and UNIX raster drivers for their printer models should they choose to do so. CUPS always takes care of the first stage of rasterization so these vendors do not need to care about Ghostscript complications (in fact, there are currently more than one vendor financing the development of CUPS raster drivers). This is illustrated in the CUPS-Raster Production Using Ghostscript illustration.

Figure21.7.CUPS-Raster Production Using Ghostscript.

CUPS versions before version 1.1.15 shipped a binary (or source code) standalone filter, named pstoraster . pstoraster , which was derived from GNU Ghostscript 5.50 and could be installed instead of and in addition to any GNU or AFPL Ghostscript package without conflicting.

Since version 1.1.15, this feature has changed. The functions for this filter have been integrated back into Ghostscript (now based on GNU Ghostscript version 7.05). The pstoraster filter is now a simple shell script calling gs with the -sDEVICE=cups parameter. If your Ghostscript fails when this command is executed: gs -h |grep cups , you might not be able to print, update your Ghostscript.