PURPOSE: To define one of color parts in the two colors of comparatively close hue as a mask area and to exclude the other color part from the mask area by preparing a mask corresponding to the value of a first coefficient at each picture element in a color image.

CONSTITUTION: The image data of the color image are read by a reading scanner 36 and stored in an original image memory 22. The image stored in the original image memory 22 is displayed on a color CRT 38 and on that color image, a user respectively designates an object color to be clipped and a color out of the object. A matrix arithmetic part 50 performs processing to respectively calculate the color vectors of the object color and the color out of the object and to calculate a matrix. A multigradation mask arithmetic part 52 reads the picture element values of respective picture elements in the color image from the original image memory 22 and calculates their coefficients. Next, the coefficient of the first color vector is extracted from the provided coefficients and stored in a multi-gradation mask memory 28. The first coefficient shows the strength of the first color vector in the colors of respective picture elements.