| 摘要 |
PURPOSE:To remove the influence of disturbing light, to reduce the quantity of light emission of a light source, and to reduce the power consumption and heating value by subtracting the signal of only the disturbing light from the photoelectric conversion signal of an image where a grating image and the disturbing light overlap with each other. CONSTITUTION:The light from the light source 1 is given a uniform intensity distribution by a diffusion plate 2 to illuminate a grating 3. Transmitted light from the grating 3 is passed through a lens 4 and a sample surface 8 to form an image on a CCD 5, thereby obtaining a real image of the grating 3. In this case, when a measurement switch is pressed, an internal CPU unit 12 opens a shutter 15 to measure the composite value of the signal component of the grating image and the noise component of the disturbing light, and then closes the shutter 15 to measure only the noise component of the disturbing light, which is subtracted from the composite value to obtain the signal component of the grating image. Then peak points corresponding to light parts or bottom points corresponding to shade parts are extracted and further pitches Pi are extracted; and standard deviation delta is computed from the pitch data by using an equation and displayed as the flatness of a material surface 8 to be measured 8 on a display device 10.
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