1. An image processing method of extracting a target object from a target image and carrying out a specified image processing by causing a computer of an image processor for processing color images from a color image taking device to execute a program stored on a computer-readable memory medium, said target image being a color image which is a combination of color data corresponding to a plural n-number of different hues, said method comprising: a first step of obtaining a reference image by an image-taking means in the absence of said target object in the field of vision of said image-taking means; a second step of considering those of said color data corresponding to specified less than n of said different hues and extracting difference both in magnitude and in direction in the degree of intensity of said considered color data relative to said combination of color data corresponding to n different hues between each pixel of said target image containing said target object and a corresponding pixel on said reference image; and a third step of extracting those of said pixels of said target image for which the difference extracted in said second step is greater than a specified threshold value and is in a specified direction and recognizing an image area formed by the extracted pixels as said target object.