PURPOSE: To realize improvement of picture quality by keeping continuity of contours of a picture without almost causing a defect when a picture is threshold processed.
CONSTITUTION: An image area discrimination section 12 discriminates contours of a picture at a noted picture element based on multi-value picture data 15a being the noted picture element, multi-value picture data 15b being a picture element of a preceding line and multi-value picture data 3a being a picture element of a succeeding line. A state probability discrimination section 13 discriminates in which of main scanning or subscanning directions the consecution is in existence depending on each state of binary data 6a of a preceding picture element, binary data 17a of a picture element of a preceding line and multi-value picture data 5a of a succeeding picture element when a noted picture element is located at a contour part according to the result of discrimination 12a. A threshold level selection section 11 selects a desired threshold level among 1st-3rd threshold levels according to the result of discrimination 13a.
ASADA AKIHIRO
IMAZAWA KOJI
TANAKA SEIJI
