1. An image processing apparatus comprising: an image acquisition unit configured to acquire a projection pattern including a plurality of symbols, projected by a projection unit, and an image including a subject onto which the projection pattern is projected by the projection unit; a first calculation unit configured to associate a first area in the projection pattern with a second area in the image; a second calculation unit configured to calculate a position of a symbol corresponding to a symbol in the first area, within the second area in the image, based on a calculation result obtained by the first calculation unit; and a measurement unit configured to measure a three-dimensional shape of the subject based on the position of the symbol calculated by the second calculation unit.