BINARIZING IMAGE PROCESSING METHOD FOR MULTI-GRADATION DATA AND IMAGE PROCESSING UNIT ADOPTING THE METHOD

摘要

PROBLEM TO BE SOLVED: To smooth gradation and to enhance image quality by suppressing tailing and delayed starting of a highlight part of a gradation image and production of stripes to a transition part from the highlight part to a middle tone part which are caused by binarizing multi-gradation data by the error spread method. SOLUTION: An error distribution coefficient of a highlight part to be distributed in the main scanning direction is selected higher than the total sum of the coefficient in the subscanning direction, and the error distribution coefficient for a part from the end of the highlight part to a middle tone part is selected to be a median of the error distribution coefficient of the highlight part and the middle tone part. Moreover, the error distribution coefficient of the middle tone part is selected for the error distribution coefficient of the part after the middle tone part. Relating to this processing unit, an error distribution coefficient acquisition circuit 3 applies an error distribution coefficient to gradation data classified into three stages by a gradation share circuit based on gradation of received data 1 so as to conduct error distribution processing for the data and provides an output of binarized data.