A method for compensating scattering includes acquiring the projective length of non-subject entities and acquiring the projective length of an object of radiography wherein the object of radiography is radiographed with a beam thickness set to the same value as a detector thickness and the object of radiography is radiographed with the beam thickness set to a value larger than the detector thickness. An amount of scattering is calculated based on the difference between the object data from the first scan and the object data from the second scan and stored in association with the sum of projective lengths. A subject is radiographed to produce data and the projective length of the subject is calculated along with the projective length of the non-subject entities having affected the data. The amount of scattering associated with the sum of the projective length and the projective length is then determined.