<正>Objective: To study the effective computerized image processing of underexposed and overexposed X-rays of bones and joints. Methods: Ninety-nine conventional X-ray images （82 were overexposed and 17 were underexposed）

scanned by an UMAX Astra 4000U Scanner

were converted into digital images on the basis of their analog images. A computerized imaging processing program consisting of five functional modules such as Contrast Stretch

Fast Flourier Transform （FFT）

Image Smoothing Modules

Inverse Fast Flourier Transform （IFFT） and Nonlinear Transform performed image contrast stretch and smoothing. Three senior doctors from hospital image sections made their evaluation of all the processed images. Results:Of 82 overexposed films

71 met the clinical requirements after image processing

and 11 were unable to be applied to clinical diagnosis

accounting for 87% and 13% respectively. Of the other 17 underexposed X-ray images

11 met the clinical requirements while 6 were not

making a percentage of 64 and 35.