Image processing apparatus, image processing method, and non-transitory computer-readable storage medium

An image processing method of an image processing apparatus that generates an image of a first material and an image of a second material contained in an object, the image processing method comprising

• a processing step of performing energy subtraction processing using information concerning a plurality of attenuation rates corresponding to a plurality of radiation energies that are different from each other and are obtained by performing imaging in which an object is irradiated with radiation,
• wherein in the processing step,
• a linear attenuation coefficient of the first material at an energy of the radiation is estimated, (a) using at least one of information concerning an effective atomic number and information concerning a surface density that are obtained by the energy subtraction processing, or (b) using at least one of information concerning a thickness of a third material and information concerning a thickness of a fourth material that are contained in the first material obtained by the energy subtraction processing, and (c) using a linear attenuation coefficient of the third material, a density of the third material, a linear attenuation coefficient of the fourth material, and a density of the fourth material, and
• an image of the first material and an image of the second material is generated using the linear attenuation coefficient and the information concerning the plurality of attenuation rates.