Abstract: The invention relates to a process for compensating for effects related to variations in the velocities of electrically charged ink drops (40) in a jet (4) output from a print head of a printer, the drops being electrically charged by charge electrodes (30), consisting of: measuring the velocity of the jet on the downstream side of a drop charge zone, and calculating a variation in this measured velocity, for each drop, determining a voltage correction value to be applied to the charge electrodes, as a function of said measured velocity variation.

Abstract: The invention relates to a preparation process for printing of light patterns on a dark background, on a surface (S) moving along a direction, using a set of jets in a print head, comprising the following for each jet in this set of jets:—an estimate of the disturbance on the print quality of this jet, resulting from the lack of printing by each of a plurality of other jets in said head,—determination of a correction to the jet as a function of the previous estimate, to compensate said disturbance.