PURPOSE: To obtain a processing method which is well suited to a picture display device of pattern system, by comparing the data on the picture element to be displayed with the data on each of three picture elements on a line which are displayed immediately before or after the line and applying the half-dot processing to the first or second half of the data to be displayed in response to the result of the above-mentioned comparison of the data.

CONSTITUTION: The 1st inverter 4 and the 1st and 2nd D flip-flops 5 and 6 are used to extract simultaneously data D3, D4 and D5 equivalent to each picture element out of the front and back lines within the preceding 2nd shift register 3. While the 2nd inverter 7 and the 3rd and 4th D flip-flops 8 and 9 are used to extract simultaneously data D1, D0 and D2 out of the data on a display line within the preceding 1st shift register 1. Then it is decided whether the half-dot processing is applied to the second 1/2 picture element component of the picture element data D0 on the display line by the 1st AND gate 10 as well as above-mentioned inverters and flip-flops. At the same time, the 2nd AND gate 11 and those inverters and flip-flops decide whether the half-dot processing is applied to the first 1/2 picture element component of the data D0.