Tone Correction of Digital Half Tone Obtained by Ordered Dither Method

Abstract

The ordered dither method has been widely used for conversion from continuous tone image to digital half tone. In this method, however, the threshold to obtain the bi-level image is determined by the dither matrix without the consideration of the density distribution of an original picture. It is considered as one of causes which make the tone reproduction of digital half tone poor.
Based on the concept “ON probability” calculated by comparing density of each pixel in the original picture with the dither matrix, a new method is proposed to determine the threshold of dither matrix for conversion to bi-level image.
The method is successfully applied to tone correction of digital half tone by using an ink-jet printer.