| 摘要 |
PURPOSE: To detect the edge position of an object to be measured with high accuracy, regardless of the shape of the object and the existence of a disturbance such as a noise. CONSTITUTION: A signal from a photoelectric converter 3 is first converted into a digital signal Di having a picture element address. A differentiating circuit 5 outputs a differentiated valueΔDi, and a local change rate operation circuit 6 outputs a local change rateΔDiN, respectively upon receipt of the signal Di. Also, a comparator 9 outputs a gate control signal, only when the value ofΔDiN is equal to or above a threshold, and a gate circuit 8 outputs only the value ofΔDi among the inputted values ofΔDi, upon receipt of the gate control signal as well, thereby, limiting the area ofΔDi data. A maximum differentiated value detection circuit 10 outputs a maximum differentiated valueΔDimax among the limited data and the adjacent differentiated values thereof. In addition, a gravity position operation circuit 11 calculates the gravity position PG for the values. The PG so obtained shows an edge position.
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