A print filter can be as simple or as complex as needed. The Oracle Solaris OS provides print filters in the /usr/lib/lp/postscript directory that cover most situations where the destination printer requires the data to be in PostScript format. If you need filters for nonPostScript printers, you have to create the filters and add them to the systems that need filters.
A set of print filter descriptor files are provided in the /etc/lp/fd directory. These descriptor files describe the characteristics of the filter (for example, fast or slow filter). These description files point to the filter program (for example, to /usr/lib/lp/postscript/postdaisy).