Real-time defect detection in video images

In this paper we present a method for the real-time detection of defects in pel iodic structures. Video images play an important role in automated manufacturing and quality, control. The video image of the object to be inspected is displayed on a liquid crystal display (LCD), which modulates a coherent read-out beam. The modulated coherent beam is Fourier trans formed with the help of a lens and is filtered from all periodic components by a nonlinear optical element. As nonlinear optical elements photorefractive crystals and optically addressed liquid crystals cart be applied. After a second Fourier transform only defects remain visible in a resulting image. In this paper we discuss the procedure and present examples in order to demonstrate the ability of filtering technical objects like the grid of a solar concentrator cell.