1. An image processing method comprising: acquiring an input image produced by image capturing using an optical system; acquiring a first noise amount contained in the input image; performing a resolution enhancement process on the input image; performing frequency decomposition of the input image into multiple decomposed images that are mutually different frequency band components; calculating, on a basis of the first noise amount and a frequency characteristic of the resolution enhancement process, a second noise amount contained in each of areas of each of the multiple decomposed images; performing a noise reduction process on each area of each decomposed image on a basis of the second noise amount calculated for that area; and combining the multiple decomposed images each subjected to the noise reduction process together.