Detection of foreign material included in LCD panels

A method of detecting foreign materials in the visual inspection of an LCD with its protective film in place, without being affected by scratches or dust on the surface of the protective film, is described. In this method, which is based on the light-section method, a fan-beam laser light is scanned over the surface of the LCD to obtain a set of light-section time-series images. Those images are composed into a horizontal cross-section image for the specified depth and internal foreign materials are detected from that image. By using commercially available 1300 by 1030 pixel high-resolution CCD cameras, fibers as small as 50 μm in diameter can be detected. Furthermore, by selectively reading a specified region of the camera image, the 600 frame/s image reading speed that is required for in-line inspection can be attained