PURPOSE: To make the various kinds of gradation processing possible by converting the number of the gradations of inputted image data, binarizing that number later and instructing the number of gradations.

CONSTITUTION: For the image signal of an original from a sensor 1, shading correction is performed through an AMP 2 and an A/D converter 3 by a shading correction circuit 4, and the RGB position deviation of the sensor 1 is corrected by a color slurring correction circuit 5. Next, a black character area is detected from image data by a black character detection circuit 6, a black character signal is outputted, and the image is enlarged or reduced by a power varying circuit 7. Then, corresponding to a control signal from a control signal generation circuit 9, a logarithm conversion circuit 10 converts an RGB space into a CMY space based on a conversion table from a CPU 21. A minimum value extraction circuit 11 extracts the minimum value of CMY image data, a masking UCR circuit 12 performs masking and UCR processing and outputs CMYK image data, and a spatial filter obtains smoothing data. A gamma conversion circuit 15 converts the image data into designated density by performing γconversion, and a binaizing circuit 16 outputs binarized image data.