Automated quality inspection of surface defects on touch panels

Capacitive touch panels (CTPs) with advantages of water-proof, stain-proof, scratch-proof, and fast response are widely used in various electronic products built in touch technology functions. It is a difficult inspection task when defects imbedded on surfaces of CTPs with structural textures. This research proposes a Fourier transform-based approach to inspect surface defects of CTPs. When a CTP image with four directional and periodic lines of texture is transformed to Fourier domain, four principal bands with high-energy frequency components crisscross at the center of Fourier spectrum. A multi-crisscross filter is designed to filter out the frequency components of the principal band regions. The filtered image is then transformed back to spatial domain. Finally, the restored image is segmented by a simple threshold method and defects are located. Experimental results show the proposed method achieves a high defect detection rate and a low false alarm rate on defect inspection of touch panels.