To provide a technique of obtaining information for discriminating two substances included in a radiation image of a subject without performing imaging by changing radiation energy, a radiation imaging system includes a detector including a plurality of pixels which obtain pixel values corresponding to incident radiation transmitted through a subject, and an information processing unit configured to perform a process of estimating information on thicknesses and densities of substances included in the subject by performing a calculation using pixel values of an arbitrary one of the plurality of pixels and an average value of energy of radiation quanta of the arbitrary pixel calculated in accordance with the pixel values of the arbitrary pixel.
