Automatic Surface Inspection for Directional Textures Using Discrete Cosine Transform

A new global image restoration scheme using discrete cosine transform (DCT) is proposed in this paper. This DCT-based image restoration scheme can be used for inspecting the defects in directional texture surfaces automatically. The input spatial domain image is first transformed into DCT domain. The dominating directions of the textures in the input image will be compacted to orthogonal straight lines, respectively, throughout the direct current (DC) component in the spectrum. The linear primitives associated with high-energy frequency components in the DCT domain are eliminated by reducing them to zero and then transformed back to the spatial domain. This procedure will have all directional textures be blurred and will preserve only local defects if they are initially embedded in the input image. Experiments on a variety of product surfaces with directional texture such as straight, slant, orthogonal, and slant orthogonal linear primitives are given to demonstrate the effectiveness and robustness of the proposed method.