Energy difference image processing method

An energy subtraction picture processing method comprising the steps of:

• (a) employing a semiconductor radiation detector to detect X-rays which have penetrated an object and to provide output signals representing the detected X-rays;
• (b) providing a pair of discriminating levels for dividing said output signals from said detector representing the detected X-rays into a high level energy band and a low level energy band;
• (c) obtaining logarithmically converted data S(L) of the X-ray picture formed by a counted value of x-ray photons in said low level energy band, said logarithmically converted data being defined as S(L)=-ln(I(L)/I.sub.0 (L)) where I.sub.0 (L) indicates incident counts of low energy X-rays and I(L) indicates one of (i) counts of low energy X-rays which have penetrated the object and (ii) low energy X-rays which have penetrated the object;
• (d) obtaining logarithmically converted data S(H) of the X-ray picture formed by a counted value of x-ray photons in said high level energy band, said logarithmically converted data being defined as S(H)=-ln(I(H)/I.sub.0 (H)) where I.sub.0 (H) indicates incident counts of high energy X-rays and I(H) indicates one of (i) counts of high energy X-rays which have penetrated the object and (ii) high energy X-rays which have penetrated the object;
• (e) obtaining an exponential function {S(L)}.sup.y of S(L), said exponential function being defined as {S(L)}.sup.y ={-ln(I(L)/I.sub.0 (L))}.sup.y ;
• (f) obtaining an exponential function of S(H), said exponential function being defined as {S(H)).sup.x ={-ln(I(H)/I.sub.0 (H)}.sup.x, where x and y are selected from the group comprising zero, negative numbers and non-integer positive numbers with x and y not being simultaneously selected to be zero;
• (g) multiplying S(H), S(L) and {S(H)}.sup.x, {S(L)}.sup.y, respectively, by predetermined constant coefficients a.sub.1, a.sub.2, a.sub.3 and a.sub.4, where a.sub.1 is selected from the group of integral numbers, and a.sub.2, a.sub.3 and a.sub.4 are selected from the group of non-integral numbers;
• and
• (h) performing addition of S(H), S(L), {S(H)}.sup.x, and {S(L)}.sup.y multiplied by the predetermined coefficients a.sub.1, a.sub.2, a.sub.3 and a.sub.4, respectively, in step (g), so as to provide a picture from which a particular one of the materials constituting the object is selectively extracted or removed.