We have proposed a novel algorithm for detecting scan alluk on the surface of a TFT-LCD device that is generated by non-uniform exposure during fabrication. The scan alluk is known to have similar intensity values on paths that are determined by the shape of lens for light exposure. Based on the observation, the proposed algorithm inspects the uniformity on the paths using 1D projection image of 2D LCD image and 2D backprojection image of the 1D image. We have shown the usefullness of the proposed method by theoretical analysis and experimental results.