The degradation due to the quantum mottles of X-ray images causes lnany difficulties in medical diagnosis. In this paper, by especially introducing the general type image processing rnethod of X-ray images on the basis of the actual physical formation process, a ne、 v restoration method for the noisy image is proposed.A/1Qre specifically,as a noise removalrnethod for the quantum mottles,a digital filter of a stochastic type considering the specific statistical propertiё s reflecting the

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... ity of variance of quantum mottles is newly derived on the basis of Bayes'theorenl suitable for the recursive image processing. Finally in order to confirrn the effectiveness of the proposed method, it is applied to one of the actual rnedical images. INTRODUCT10N In the field of actual rnedical diagnosis using an X-ray,the fairly、 veak X-ray intensity is usually used in order to reduce the X-ray exposure to a human body.Accordingly,the radiographic screen一 filrn system has been employed for improving the sensitivity of film. In this case, however, the quantum mOttleも increase in a、 veak X-ray photograph owing to the proper spatial fluctuation of X一 ray quanta produced by an X-ray tube. Furthermore, there happens a specific situation that the variance of the quantum mottles depends on the amount ofirradiation by the X-ray.′ 「 he above degradation of X一 ray image rnakes very often a lot of difficulty in the medical diagnosis. Up to no、 v, many restoration methods of the degraded irnage have been investigated by many researchers〔 1-9〕 ,Almost all of them)howeve,were confined only to the methods due to the leastsquares error criterion for processing gray levelso Especially in the lnedical field,the purpose of the image processing is not to propose an artificially effective methodology,but to detect its true mediむ alimage as exactly as possible.Therefore,it is not principally reasonable to use directly the above artificial restora-*l Faculty of Engineering,Kinki University:〔 Higashihiroshilna city,729-17 Japan〕 *2 sch。 。 l of Dentistry,Hiroshirna University