1. An image processing apparatus comprising: a detection unit that detects a subject region based on image data; an obtaining unit that obtains a value indicating a difference between light and dark parts of the subject region; a generation unit that generates a non-linear conversion characteristic by interpolating a plurality of non-linear conversion characteristics using the value indicating the difference between light and dark parts; and a correction unit that applies the non-linear conversion characteristic that was generated by the generation unit to the image data.