Mustererkennungsgerät

An apparatus for determining the probability that the shadow of a tumor designated on a radiation image of an object is the shadow of a malignant tumor on the basis of an image signal representing the radiation image includes a spectrum calculating means, a characteristic value calculating means, and a judging means. The spectrum calculating means obtains the spectrum distribution of the image signal D(r, theta ) whose coordinates are expressed in polar form with the origin taken as the approximate center of the shadow. From the spectrum distribution the characteristic value calculating means obtains a characteristic value, which the judging means uses to determine the probability that the shadow of a tumor is the shadow of a malignant tumor.