Using pswrite Device, setscreen operator seems to get lost. After processing
a PS or PDF file containing setscreen / halftone dictionary all of this
information e.g. Frequency, Angle SpotFunction is lost.
When the output (separated file) is sent to an imagesetter, all colors are
rasterized with the same angle.

The same problem occurs with the pdfwrite device.

Here is the test snippet:
%%%%%
<< /PageSize [100 100]>> setpagedevice
 
/DeviceGray setcolorspace
 
65 25 { exch pop abs neg } setscreen
 
.5 setgray
4 setlinewidth
0 0 moveto
100 100 lineto
stroke
 
showpage