Bi-level halftone processing circuit and image processing apparatus using the same

摘要

An upper limit value and a lower limit value are used to modify the correction value computed in a correction value computing circuit in such a way that the correction value ranges between the upper and lower limit values. The threshold value computed from the upper and lower limit values is compared with the modified value to compute a binary value. The upper and lower limit values are selected to become those which the correction value may take. The correction value is obtainable in conformity with the density value resulting from converting the density value of an object pixel of an original image in terms of an exponential function or the approximate function of it.