1. An image processing apparatus comprising: a filtering process unit that performs an image filtering process that includes a plurality of times of filtering processes with respect to original image data to acquire processed image data, wherein in each of the plurality of times of filtering processes, the filtering process unit applies a filter to processing target data to acquire filter application process data, applies a gain to the filter application process data to acquire gain application process data, and acquires filtering process data from the gain application process data, and wherein in each of the plurality of times of filtering processes, the gain applied to the filter application process data is acquired based on a target frequency characteristic of the image filtering process specified based on an individual optical characteristic of an optical system used when the original image data is acquired.