Binarization using a local average, and using error diffusion

摘要

There is provided an image processing apparatus such as facsimile apparatus or digital copying machine for digitizing image data into two values or multi-values. The apparatus comprises: an input device to input data of a target pixel to be digitized; a calculating circuit to obtain an average density value of a predetermined region; a digitizing circuit such as a binarizing circuit for digitizing or binarizing the target pixel data on the basis of the average density value obtained by the calculating circuit; and a correction circuit to correct a difference which occurs upon digitization by the digitizing circuit. The calculating circuit calculates the average density value m1 of the pre-determined region when the target pixel data was binarized to 1 and the average density value m2 of the predetermined region when the target pixel data was binarized to 0 by using a predetermined weighting mask. The digitizing circuit binarizes the target pixel data by using (m1+m2)/2 as a threshold value. When the difference between the target pixel data and the average density value is within a predetermined value, the difference is corrected, so that an image of excellent gradation can be reproduced. When it is equal to or larger than the predetermined value, the difference is not corrected, so that the resolution of a character portion such as an edge portion can be improved.