JPS6457877A - Area identification method for picture processor - Google Patents

Abstract

PURPOSE:To realize sure area identification with simple hardware by providing a frequency characteristic to a scanning window and providing a level difference detection function. CONSTITUTION:A 3X3 scanning window is set around a noted picture element P5 and the surrounding picture elements P1-P4 and P6-P9 except the noted picture element P5 are split into four blocks by picture elements connected in the main and sub scanning directions. Each picture element is weighted in each block and the average value or total sum of the weighted picture element data is obtained in each block, then the density in each block has a specific frequency characteristic. Thus, in selecting the frequency characteristic as a low pass filter characteristic, the dot print component in the original picture is eliminated. As to the picture data whose dot print component is eliminated, a difference between block pairs clipping the noted picture element in between is obtained. Since the difference corresponds to the degree of the density change, a binary picture area and a halftone picture area can be identified by comparing the difference with a preset threshold value.