1. An image processing apparatus comprising: an image acquisition unit configured to acquire a plurality of partial images obtained by shooting each of a plurality of shooting ranges which a shooting region of an object are divided into; a feature amount acquisition unit configured to acquire a feature amount of at least one of the partial images; a characteristic acquisition unit configured to acquire a gradation conversion processing characteristic based on the feature amount and the shooting region; and a conversion unit configured to convert, based on the processing characteristic, a gradation of an image of the shooting region of the object obtained by joining the partial images.