While removing noise, the loss of useful information is inevitable, especially the edge information of linear images. To maximize the image and minimize the loss of useful information according to the edge features of the testing image, a window with appropriate size and shape was selected to perform median filtering and other operations. It is innovatively proposed to apply a Hough transform to the filtering window shape selection of the wheel crack CT image, aiming at the image of the single direction contour. The Hough transform was used to detect the direction of the contour, and the corresponding shape window was used to filter the crack. This method was compared with the traditional method, and the image with better visual effect can be obtained after pre-processing by Hough transform. In this paper, to improve the filtering effect for images with multi-direction edge contours, an oblique filter is designed according to the pixel gradient. The data shows that the peak signal-to-noise ratio (PSNR) of the image after proposed filtering is improved by 4-6 compared with the traditional median filter. The structure similarity (SSIM) is increased by approximately 1%-2%. Three-dimensional images are obtained using the stack of CT images of buckwheat slices. The filtering result of the proposed method is favorable by the contrast of before and after.