1. An image processing apparatus, comprising: a multi-resolution decomposition part configured to repeatedly decompose a first image in which pixels thereof are arrayed in two-dimensional or three dimensional directions into high-frequency components and low-frequency components until the number of pixels becomes a predetermined number in each of the directions, and generate a second image based on the low-frequency components in a result of the last decomposition; an adjustment part configured to adjust the brightness of the second image; and a restoration part configured to restore image having the same number of pixels as that of the first image in each of the directions using the brightness adjusted second image.