1. An image composition apparatus comprising: an information acquisition unit that acquires numerical values relating to brightness of pixel regions with a particular color in data of any image among data of a plurality of images that are sequentially captured with an exposure duration being varied; and a synthesis unit that performs pixel addition of the data of the plurality of images by changing a degree of addition of the data of the plurality of images, based on the numerical values acquired by the information acquisition unit, and generates data of a composite image whose dynamic range is widened.