PURPOSE: To improve half tone expression performance and to attain quick processing by matching tone grade expression performance between input and output each other in a digital half tone forming system expressing half tone by dot configuration.

CONSTITUTION: The information of an original is inputted to a photoelectric conversion part 104 and converted into corresponding electric signals, which are compressed and converted into 8-bit digital signals 111W113. Respective upper 4- bit signals 114W116 out of these signals 111W113 are supplid to a color conversion table 120 and respective lower 4-bit signals 117W119 to a color conversion table 121. These complementarily color-converted 4-bit data are supplied to signal composing circuits 128W130, the picture patterns of the basic density patterns are read out by positional information 131 from respective counters 155, 156 and a required pattern is stored. Thus the basic density patterns in the output side can be distributed two-dimensionally and uniformly by the information in the input side and the positional information to be recorded.