Automatic Defect Inspection of Patterned TFT-LCD Panels Using 1-D Fourier Reconstruction and Wavelet Decomposition DU-MING TSAI*, CHUNG-YU HUNG

Large-sized flat-panel displays have become increasingly important for use in PC monitors and TVs. In this paper we have considered the problem of automatic visual inspection of micro-defects including pinholes, scratches and particles in patterned Thin Film Transistor-Liquid Crystal Display (TFT-LCD) panel surfaces. For large-sized TFT-LCD panel inspection, high resolution line scan is demanded. We propose a global 1-D Fourier-based image reconstruction scheme that directly works on the 1-D line images, instead of the traditional 2-D area images. The proposed method fully utilizes the inherent geometric structure of a TFT-LCD panel. It first eliminates the frequency components that represent the periodic pattern of a TFT-LCD line image in the 1-D Fourier spectrum, and then back-transforms the 1-D Fourier-domain image to the 1-D spatial domain image using the inverse Fourier transform. The Fourier reconstruction process can effectively remove the patterned background and distinctly preserve local anomalies in the resulting 1-D image. Wavelet decomposition is further applied to remove uneven illumination in the filtered image so that defects can be easily segmented with simple statistical control limits. Experimental results on a number of micro-defects embedded in TFT-LCD panels show that the proposed method can reliably detect various ill-defined defects without designing and measuring the quantitative features of individual defect types