A METHOD FOR IMPROVING THE QUALITY OF IMAGES USED IN DIGITAL RADIOGRAPHIC TESTING

摘要

Owing to recent developments in digital imaging technology, digital radiographic testing (RT) using computed radiography (CR) has begun to replace film RT in the inspection of piping at nuclear power plants. Digital RT enables inspection records to be preserved almost permanently without degradation and improves the efficiency of inspection by supporting inspectors using various image processing techniques. Defects can be quickly and reliably detected by applying image processing techniques such as image expansion and contrast adjustment. In addition, fluctuations in measured defect size are minimized due to quantitative evaluation using the image data. In the present paper, a method for improving the image quality of digital RT images, which is generally inferior to that of film (analog) images, is proposed in order to improve the practicality of digital RT. In this method, denoising via wavelet shrinkage and deblurring using the point spread function (PSF) estimated from image data are applied in order to accentuate the detection target in a noisy image and to improve the resolution. The enhancement of image quality is evaluated experimentally using digital RT images of a specimen with a small hole and duplex wire image quality indicator (IQI). As a result, the proposed method is confirmed to improve the quality of images with respect to noise and visibility. In particular, the visibility of the duplex wire IQI is 1.7 times.