An energy difference picture processing method comprises the steps of using a semiconductor radiation detector; providing two discriminating levels; dividing X-rays, which have passed through objects, into two kind energy zones; counting X-ray photons to obtain an X-ray picture; assembling, with corresponding coefficients, S(H), S(L), {S(H)}.sup.x and {S(L)}.sup.y, which are exponential functions of the S(H) and S(L), respectively, where S(H) is a logarithmically converted version of a picture of counts in a higher energy band and S(L) is a logarithmically converted version of a picture of counts in a lower energy band; and performing addition, subtraction, multiplication and/or division on these terms to provide a picture in which a particular one of the materials constituting the objects is selectively extracted or removed.