Sometimes in the printing of art, you want to control the screen frequency/lines
per inch(LPI) of fill areas on the output device, especially if your art is
being reproduced on a printing press. If the fill area is 50% black, the dots of
the screen cover 50% of the paper.  The LPI specifies the spacing of the dots. 
The lower the LPI, the larger the dots.  Their are various types of printing
processes, three of which I am familiar are Offset, Letterpress and
Flexographic.  Controlling the LPI of the area fills is important in matching
the capabilities of the reproduction equipment.  If you order your printing
plates from commercial plate maker, you tell them the LPI to use on your plate.
 Some vector art programs, like CorelDraw, allow setting the LPI, under
postscript settings, for individual objects on the same page or the default LPI
and overrides the default of the output device.  This is useful for graphic
effect or matching the capabilities of the reproduction equipment.  If your
produce your own plates via laser printer on polyester plates, you need to be
able to control at least the default LPI for screening fill areas.  This
function is not available in the output drivers of any typical laser printers
that I have encountered.  I use CorelDraw because it has LPI control for
postscript output devices.  I have not seen this control for other than
postscript devices, probably due to the heavy use of postscript in the printing
industry.

I am proposing, that if any developer understands how this can be done, that
this feature be added to DRAW for individual objects and the print dialog box
for the default setting for at least postscript devices.  I think this would
expand the usefulness of OpenOffice.org for the printing industry and various
graphic effects by the artist.