1. An image processing apparatus which changes a dynamic range of an image, comprising: histogram generation means for generating at least one of a density value histogram and a differential histogram of the image; LUT generation means for generating an LUT used for changing the dynamic range of the image on the basis of a histogram value in each pixel value interval of the histogram generated by said histogram generation means; and changing means for changing the dynamic range of the image on the basis of the LUT generated by said LUT generation means.