THRESHOLD PROCESSING METHOD OF DOCUMENT IMAGE

摘要

PURPOSE: To apply a threshold processing to a document image multiplexedly. CONSTITUTION: Both local and global information sets are taken into consideration to decide the number of thresholds included in an image of a gray scale. The image of the gray scale is made up of a plurality of picture elements. Each picture element has one density value. A local area of picture elements having a similar density is identified and edited into a global expression of the image. The density range is identified in a global expression in which the density of picture elements is almost constant. The density is identified in each range representing most constant points in the expression range. The number of thresholds is selected to be equal to the number of the ranges of expression.