An image processing method includes dividing a desired image into a normal region formed with partial images and a joint region formed by overlapping the partial images, first converting image data in an RGB color space corresponding to the normal region into normal region CMYK data in a CMYK color space using a normal region LUT, second converting the image data in the RGB color space corresponding to the joint region into joint region CMYK data in the CMYK color space using a joint region LUT derived based on attribute information of the printing medium and environmental information of an environment in which the printing apparatus is to perform printing, and generating printing data based on the normal region CMYK data and the joint region CMYK data.