Dither method and apparatus

Abstract

A method of creating a three dimensional halftone dither matrix, in which the matrix is divided into a predetermined number of levels with each level comprising a two dimensional matrix of activation indicators having positional values including x and y positional components. The method includes the steps of firstly creating a series of three dimensional curves, from a two dimensional array of dither values, the two dimensional array being of the same dimensions as the two dimensional matrix and including level value entries, each of the level value entries having a corresponding three dimensional curve, the three dimensional curve starting at a starting level corresponding to the dither matrix value and at a position corresponding to the x and y positional components of the level value entry, the three dimensional curve terminating at the highest level of the three dimensional halftone dither matrix and taking one x and y positional value on each level between the starting level and the highest level. Secondly, the method forms an objective function having at least two components, a first component being a measure of the evenness of the distribution of the positional values of the curves for a particular level, and the second component being a measure of the deviation of the curve from a straight vertical line. Thirdly, the method optimizes the objective function so that the positional values at any of the levels of the series of curves have a high degree of evenness of distribution and the curves have a low degree of deviation from a straight vertical line. Lastly, the method forms the three dimensional halftone dither matrix wherein the activation indicators are active in positions corresponding to the paths of each of the curves.