Picture processing method in optical measuring apparatus

A picture processing method in an optical measuring apparatus which comprises a projector for radiating a slit light on a workpiece, and an image sensing device for picturing an optical cross-sectional image drawn by said slit light radiated on the workpiece, an optical axis of said slit light and an optical axis of said image sensing device being disposed in such a positional relationship as to cross each other at an oblique angle,

• said method comprising the steps of:
• setting predetermined windows in respective portions positioned on both Y-axis sides of the optical cross-sectional image relative to a maximum portion of said optical cross-sectional image, said maximum portion being located in an X-axis direction which is defined to be such a coordinate axis on a screen of said image sensing device as to correspond to an optical axis of said slit light, said Y-axis being defined to be perpendicular to said X-axis;
• and
• measuring a position of center of gravity of each of said optical cross-sectional image in each of said predetermined windows;
• wherein a position of a tip, in the X-axis direction, of said maximum portion of said optical cross-sectional image is measured;
• two pieces of windows which are elongated in the Y-axis direction are set at a position which is a predetermined distance backwardly away from said tip in the X-axis direction;
• a position of center of gravity of said optical cross-sectional image in each of said two pieces of windows is measured;
• a reference point which has a correlation with both of said positions of centers of gravity is obtained;
• said predetermined windows are respectively set in a predetermined positional relationship relative to said reference point;
• an amount of displacement, on said screen, of said optical cross-sectional image in the X-axis direction is measured;
• a rate of magnification of said optical cross-sectional image in the Y-axis direction is calculated from said amount of displacement;
• and
• at least the positional relationship in the Y-axis direction relative to said reference point and the size in the Y-axis direction of said predetermined windows are changed depending on said rate of magnification.