Abstract: The present invention offers a system which operates with reference to a dictionary for registering a registered data string as correlated to a registration number and for performing a data compressing process by replacing a combination consisting of two or more character strings with a registration number mentioned above. The system according to the present invention performs the compilation and updating of the dictionary at the Step A1 and A2, respectively, and judges at the Step A3 whether or not the dictionary has become the optimum dictionary. The system performs the updating of the dictionary in such a case by an incremental decomposition method, or an augmentative decomposition method, or the like.

Abstract: Bit map data stored in an image memory is read every one column by N lines or M columns by one line and is stored in a shift register of M bits by N bits. The data in the shift register is differentiated in the direction of the column direction by edge detectors and extracted as data representing only a contour portion. This contour data is classified into forms of discontinuous points with respect to the horizontal direction and the vertical direction by classifying circuits. As for the classified data, the size of a dot to be printed and a printing position are converted by a determining circuit to a pulse width and a timing at which the dot is to be generated, and the classified data is converted to a pulse width by a pulse-width modulating circuit and is outputted to a laser beam modulating device. As a result, a dot smaller than a normal dot is added in a vacant portion, or a part of a normal dot is shaved, thereby printing a smooth pattern.