A couple of people seem to think you mean posterization, but since you said “halftone color separation” I assume you mean for process color. Your best bet is probably to send your files to a service bureau. I used to work a place that did large format screen printing and we sent out our separations, even though our presses were far larger than the bureau’s image setter, and we still had to enlarge the separations to get the films to burn the screens (which means we hade large mural enlargers and procsseors, but we still end out the separations). Color separation tends to be a rather specialized field. However, there is some capability to output separations in Photoshop, especially with Postscript printers. Or you cold experiment with the “pixilate / color halftone” filter (if it is still there, I haven’t been buying updates so I’m using an old version 4.0 lol ) Or one can split the CMYK channels into separate files and change the mode to bitmap using the various screening options, whic