1. An image processing method for removing a noise component contained in an original image, comprising: extracting a noise component contained in an original image in a work color space; creating a noise-free image in the work color space based upon the extracted noise component and a ratio between a differential of gradation characteristics in an output color space and a differential of gradation characteristics in the work color space; converting the noise-free image in the work color space to an image in the output color space.