px2ps converts a number of graphics formatted files to Encapsulated Postscript format. The advantage of using this utility is that is preserves colour (other packages may not be able to handle colour).
Some of the format the package handles are .tiff, .ras, .rgb and .targa.
The package can also send the output directly to a specific command (i.e. the printer), centre the image, scale the image and rotate the image as well as other features.
For example
px2ps tiger.rgb | lpr -Pcolourwould send an EPS version of tiger.ps to printer colour.
Issuing the command itself will display its usage.