| 摘要 |
PURPOSE:To obtain an economical apparatus having simplified structure which results in less misdetection by extracting combination of two positions from the detected positions, calculating the center of them and by determining the true center based on the distribution of such center. CONSTITUTION:A sampling circuit 7 receives a picture signal of interference fringes, a memory 9 stores in correspondence the picture signals output from an A/D converter 8 and a level sampling position detecting circuit 10 obtains the sampling positions having a level, extracts all combinations for selecting two positions and obtains the center position CPnm of sampling position of respective combinations. A center appearing frequency distribution generating circuit 12 searches distribution of appearing frequency of CPnm output from the center calculating circuit 11. A center detection circuit 13 determines the center where the appearing frequency becomes maximum as the true center of the alignment target based on the distribution of appearing frequency being generated. |
