A method to detect mura, which is defined as irregular lightness variation on uniformly manufactured surface, is necessary to keep quality of the display devices. The mura is understood as defects without clear contour or contrast which gives viewers unpleasant sensation, whose level of liquid crystal display panels is standardized at Semiconductor Equipment and Materials International. We propose a method to detect mura of the display devices' components that have lower intensity than the final device with some background pattern.