The aplication of low-pass filtering to pretreatment in thermal wave NDT

The contrast is low, and the noise is strong in infrared images, which go against defects judgment and recognition. In order to resolve those, limitations of common methods were analyzed. Then, on this basic, grayscale value adjustment method and low pass filter method was proposed to be introduced. Image enhancement steps were designed and thermal image was processed in grayscale value adjustment method and low pass filter method in turn. In process of image enhancing, the index selection was studied in gray value adjustment method. And the effect was ideal, when it was 3. After that, the infrared image was treated in ideal low-pass filter, Butterworth low-pass filter and index low-pass filter. Contrasted effects of these methods, smooth effect would be the best in using index low-pass filter. After image processing, comparing the original image and processed image, it could be found that enhancing effect was good, which verify the validity of this method. And an effective way was designed for heat waves image enhancement.