AM screening (halftoning) often suffers from periodic patterns in single separation. Since these disturbing patterns become stronger as the printer's resolution decreases, they pose a real challenge to laser printers & inkjets as they compete against offset presses.We present a formula for predicting the frequencies and amplitudes of these disturbing patterns, based only on the geometric structure of the screen. An automatic filter, based on this formula, was constructed. This filter passes only 4% of the potential screens, without the need to construct the screen matrices, and without print, thus reduces testing time drastically. At the next stage, the method was generalized to handle interference between the screen and machine frequencies.This filter became a vital tool in screening development for HP-Indigo machines. It served us well in the construction of all of our latest high ruling screens. Currently, this tool is also used to generate an AM screen for the commercial inkjet developed by HP-Vancouver, and the results are promising.A patent application was submitted, concerning both the filter and the fine geometries which it passes (international application PCT/IL00/00079, publication number WO0158140, filed on 06/02/2000).