Method and apparatus for detecting run length of two successive pixels and subjecting run length to universal coding

A halftone image data compression apparatus for processing a halftone image, comprising:

• first means for detecting a continuous state of pattern data of two successive pixels on a line of a halftone image for N adjacent lines of the halftone image, where N is an integer;
• second means, coupled to said first means, for detecting run lengths of the continuous state detected in said first means along a direction of the lines;
• and
• third means, coupled to said first and second means, for subjecting to a universal coding time-sequential data which is in predetermined processing units, each of the predetermined processing units being made up of one of the run lengths which is detected by said second means and corresponding pattern data which are received from said first means while the continuous state is detected for said one run length.