🚀 go-pugleaf

As there is an obvious trade off between spatial resolution and
intensity resolution in halftones, I've found that you can often do
better than the default screen frequency if you know how many grey
levels are in your image. (The default screen parameters imply ~32 grey
levels at 300 dpi.) We have been experimenting with bits of postscript
code for our images that picks a setscreen frequency based on the
current device dpi, the size and scaling of the image, and the number
of grey levels in the image. 

With the default spot function there is a lower bound on the spot
frequency below which the size of the dots becomes annoying to the
eye. Adobe Photoshop seems to overcome this by including resolution
dependent spot functions with their images! Anyone playing with Level
1 setscreen should look at some Photoshop output...

--trevor