A halftone image data compression apparatus includes a first part (21-23) 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, a second part (24) coupled to the first part for detecting a run length of the continuous state detected in the first part along a direction of the lines, and a third part (25) coupled to the first and second parts for subjecting to a universal coding a time-sequential data which is in predetermined processing units. Each predetermined processing unit is made up of one run length which is detected by the second part and corresponding pattern data which are received from the first part while the continuous state is detected for the one run length.
Method and apparatus for compressing halftone image data