Method and apparatus for controlling gradation in ink jet printer

Abstract

A method for controlling gradation in an ink jet printer is provided which includes the steps of (a) reading input picture data in first memory means (b) determining the position of a pixel under consideration from the input picture data read out from the first memory means and for calculating an error .di-elect cons.=X-X', where X is input picture data of the pixel under consideration and X' is a level of plural stages to be actually printed, (c) distributing the error .di-elect cons. to surrounding pixels around the pixel under consideration, (d) replacing the input picture data of the surrounding pixels, to which the error has been distributed, based on the distributed error, (e) performing the steps (a) to (d) for all input picture data by way of dithering, (f) storing the dithered pixel data resulting from the step (e) in second memory means, (g) generating, from the dithered pixel data read out from the second memory means, output picture data controlling the ink dot diameter of each pixel, (h) D/A converting the output picture data and (i) impressing an output voltage resulting from D/A conversion across an electrostriction oscillator of the printing head for variably controlling the diameter of liquid droplets of the liquid ink discharged from the printing head.