Provided is a computation method for obtaining information suitable for positional deviation correction and lens blur correction for a case where a part of or an entire projection image projected by each of a plurality of projectors is displayed in a superimposed manner. For this purpose, a light intensity distribution indicating a degree of lens blur of a base projector and peak coordinates of the light intensity distribution are calculated using a captured image obtained by capturing a test pattern projected by the base projector in an arrangement state in which a plurality of projectors is arranged such that a part of or an entire projection image projected by each of the plurality of projectors is displayed in a superimposed manner. Further, a light intensity distribution centered on the peak coordinates on the base projector side and corresponding to a degree of lens blur of a referencing projector is calculated using a captured image obtained by capturing the test pattern projected by the referencing projector in the same arrangement state. As a result, information indicating the degree of lens blur of the base projector and information corresponding to positional deviation and the degree of lens blur of the referencing projector are obtained.