Control process for a matrix display means displaying grey levels

Claim 1

A control process of an optical characteristic of a material for obtaining a display of 2 n different levels, said material having a plurality of zones distributed in a matrix-like manner and interposed between a first group of m rows and a second group of p columns of parallel electrodes, the rows and the columns being crossed, a zone MiNj of said material being defined by the rgion of the material covered by row Mi and column Nj, i and j being integers such that 1≦i≦m and 1≦j≦p, wherein for controlling the zone MiNj of the material the process includes: applying a first series of signals on row Mi for a half-cycle duration; applying a second series of signals on column Nk for said half-cycle; dividing said half-cycle into n different time fractions of different durations; giving to said first series of signals applied on row Mi, in each of said time fractions, an amplitude of a given first polarity for a duration equal to 1/m of the duration of said time fraction and a null amplitude for the remaining portion of said time fraction; giving to said second series of signals applied on column Nj a continuous amplitude for the entirety of a time fraction, said amplitude having a given second polarity, said second polarity being the same as or opposite to said first polarity; allowing change of said second polarity only when passing from one time fraction to the next; selecting said second series of signals from among a series of 2 n signals corresponding to the 2 n possible combinations of n successive time fractions having a given polarity; and reversing said first and second polarities after each half-cycle.