1. An image processing apparatus comprising: a generating unit that generates a plurality of histograms of images with respect to each color based on an input image; a calculating unit that calculates a plurality of first image densities of the images from the histograms; a receiving unit that receives a content of image quality adjustment performed on the input image; and a changing unit that changes one of the histograms based on the content of the image quality adjustment, the one of the histogram corresponding to one of the images on which the image quality adjustment is performed, wherein the calculating unit calculates a second image density corresponding to the one the images based on the one of the histogram changed by the changing unit.