To obtain a satisfactory binary image where graphics are distinctly extracted even in the case of an image having a small gradation difference of variable density or an image of which the density of the background (ground) is changed.
When the density of one notice pixel is equal to or lower than a certain level, namely, a black level which has enough probability to sufficiently constitute graphics or the notice pixel is closer to the black level than peripheral pixels by a certain density difference or more as the result of comparison between the density of the notice pixel and an average density of pixels in its peripheral area, it is judged that there is much probability that the notice pixel is a pixel constituting graphics, and its density is prevented. When there is the certain density difference or less between the density of the notice pixel and the average density of pixel in its peripheral area or the notice pixel is closer to a white level, it is judged that there is much probability that the notice pixel constitute a ground, and processing is performed which multiplies its density by a certain rate so as to approximate it to the white level and preserves the density, and binarization processing is performed which judged the notice pixel to be black in the case of the density higher than a threshold and judged it to be white in the case of the density lower than the threshold.
HIRATA YOSHINOBU
MATSUZOE TATSU
NAKAMURA HIDEKI
