1. An image processing apparatus carrying out tone correction on input image data including a plurality of color components, comprising: a frequency distribution calculating part calculating a frequency distribution of tone values for at least one of the plurality of color components; a determining part determining, based on the frequency distribution calculated by said frequency distribution calculating part, whether or not tone transformation has been carried out; a tone correcting part carrying out tone correction processing on the input image data; and a switching part switching, according to a determination result of said determining part, as to whether the input image data or image data having undergone the tone correction processing is output.