An image processing apparatus includes a selecting unit selecting a reference image from input images, a calculating unit calculating brightness ratios of the remaining input images as gains, a calculating unit calculating first weights for the remaining input images and calculating a second weight based on a brightness of image data as a synthesized image of the input image with the first weights, a generating unit generating a high-contrast image by performing weighting synthesis on the input images using the first weights and the second weight, a preparing unit preparing a tone conversion curve based on a brightness distribution of the high-contrast image and a brightness distribution as conversion target, and a generating unit performing the tone conversion on the high-contrast image based on the tone conversion curve, and generating the output image having the narrow tonal range.