INSPECTING METHOD FOR SURFACE DEFECT

PURPOSE:To detect even a common defect with high accuracy by intercepting reflected light from the surface of a sample by means of a color sensor which senses every wavelength area, and detecting a surface defect of the sample based on an output signal of each wavelength area. CONSTITUTION:Reflected light which is reflected by a coating steel plate (S) travelling in the direction of an arrow and permeates into a color CCD camera 32 is converted into an electric signal in each light-inspecting element of R,G,B, and every electric signal corresponding to the R,G,B respectively is parallely processed. A differential between a raw signal which is an output of the R element and a R standard signal is processed, and a signal width, color level, and a gradation of the changes of the signal occurring when intercepted by the coating face can be extracted so that a binary coding processing can be performed surely. This processing is applied to each color signal of the G and B. Thus, since the detection of a surface defect can be performed based on color information of the R,G,B, such a subtle surface defect as a pattern, discoloration or the like that are difficult to be detected when its base is monochrome can be detected with high accuracy.