1. A method for generating an array of binary signals suitable for application to a display device to generate a halftone image in response to an array of signals characterizing a gray scale image and initial binary signals, said display device for generating spots at selected ones of regularly spaced positions on a display surface, said method comprising the steps of: (a) filtering said signals characterizing a gray scale image using a first eye-model filter reflecting characteristics of human vision to derive first signals representative of an estimate of the gray scale image as perceived by a human eye; (b) performing a sequence of steps one or more times, the sequence of steps operating on input signals and generating output signals, said initial binary signals for use as said input signals on a first pass through said sequence of steps, said output signals for use as said input signals on a subsequent pass, if any, through said sequence, said sequence comprising (i) filtering a plurality of said input signals using a two-dimensional filter reflecting characteristics representative of said display device to produce second signals representing an estimate of an output of said display device, wherein said filtering comprises forming a non-linear function of said input signals that generates said second signals, said function representing interaction of one or more displayed spots; (ii) filtering said second signals using a second eye-model filter to produce third signals; (iii) forming an error signal representative of a difference between said first and third signals; (iv) selectively modifying one or more of said input signals responsive to said error signal to produce said output signals; and (c) selecting as binary signals to be applied to said display device a plurality of binary signals comprising said output signals which plurality realizes a preselected error criterion.