ARRANGEMENT AND METHOD OF PREPROCESSING BINARY PICTURE DATA PRIOR TO RUN-LENGTH ENCODING

An improved technique for pre-processing a picture image data signal wherein a black/white image data and a halftone image data coexists, is disclosed. The pre-processing is implemented before run-length encoding. Each of line image data signals is divided into n data blocks (n is a positive integer). A reset signal is produced in synchronism with each of the data blocks when divided. Following this, a selector is supplied with a first line image data signals directly applied and also receives the first line image data via a convolution circuit to said selector. The number of transition points in each of the data blocks is counted with respect to the first line image data signal which is directly applied to said selector. Similarly, the number of transition points in each of the blocks is carried out with the first line image data signal which is applied to said selector via said convolution circuit. The comparison results of n blocks of the first line image data are stored and then applied to the selector which chooses one of the data blocks of a second line image data signal applied thereto according to the comparison results. The second line image data signal is preceded by said first line image data signal.