1. A method of calculating an image for calculating an image to be imaged by a projection optical system, comprising: acquiring a Stokes vector showing a characteristic of an illumination light; dividing the Stokes vector into a polarized light component vector and a non-polarized light component vector; dividing the polarized light component vector into a first coherent component vector and a first non-coherent component vector; dividing the non-polarized light component vector into a second coherent component vector and a second non-coherent component vector; and performing imaging calculation at least for the first coherent component vector and the second coherent component vector, respectively.