An image processing method includes determining whether image data acquired by reading a document with a reading unit is color or monochrome, saving color image data determined to be color and monochrome image data generated by monochrome conversion of the color image data, in association with each other as a learning sample, deciding a color conversion parameter to be used when image data read by the reading unit and determined to be monochrome image data is converted into a color image, using the saved learning sample, and converting the image data read by the reading unit and determined to be the monochrome image data into color image data, using the decided color conversion parameter.