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As previously stated, PostScript is the central file format to any UNIX-based
printing system. From PostScript, CUPS generates raster data to feed
non-PostScript printers.
But what happens if you send one of the supported non-PS formats to print? Then CUPS runs
“prefilters” on these input formats to generate PostScript first. There are prefilters to create
PostScript from ASCII text, PDF, DVI, or HP-GL. The outcome of these filters is always of MIME type
application/postscript
(meaning that any device-specific print options are not yet
embedded into the PostScript by CUPS and that the next filter to be called is pstops). Another prefilter is
running on all supported image formats, the
imagetops
filter. Its outcome is always of
MIME type
application/vnd.cups-postscript
(not application/postscript), meaning it has
the print options already embedded into the file. This is shown in
Prefiltering in
CUPS to Form PostScript.
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