<title>Symmetric error compensation for digital halftoning and applications</title>

Abstract

Two approaches to describe the error diffusion (ED) technique are presented, based on the image regions formed during the ED process: processed pixel area and unprocessed pixel area. According to the first approach, the ED method consists of thresholding the gray value of the current pixel to decide the binary output and then the error produced by selection of the binary output is diffused forward the unprocessed pixels. According to the second approach, the ED selects the value of the output pixel to minimize the error produced between the continuous input image and the equivalent gary level corresponding to binary output. This paper presents an ED method that unifies the two approaches. The neighbors of the current pixel to be processed are classified into two classes that are distinctly processed: on one hand the processed neighbors are used to minimize the error between the input and the equivalent gary level output and on the other hand the unprocessed pixels absorb the error produced due to the selection of the binary output. Since all neighbors of the current pixel are involved in computation, this ED approach is called symmetric error compensation (SEC). The SEC method can progress in arbitrary direction through the image area. This advantage enables the derivation of a new hybrid method between the SEC and the pulse density modulation method.