POSITION DETECTOR

PURPOSE:To delete the false subjects out of a binary picture and to ensure the detection of positions with high stability and high accuracy, by correcting the threshold value according to the check result of propriety of the binary coded threshold value. CONSTITUTION:A binarization circuit 2 binary-codes the picture signals obtained from a photoelectric scanner 1 according to the threshold value set by a threshold value deciding part 4 and supplies them to an error deciding part 3. A minor noise eliminating circuit 5 of the part 3 deletes a micropattern out of the binary pictures. A circular mask scan circuit 6 detects an area coincident with a prescribed circular mask and a major noise eliminating/coordinate detecting circuit 7 deletes a pattern of a fixed size and detects the center coordinate value and the number of detected coordinates. A checking part 8 for number of coordinates, a mutual distance checking part 9 and an area checking part 10 decide the propriety of the threshold value by means of the number of coordinates sent from the circuit 7 and the area information on a desired pattern obtained from an area counting circuit 11. If the decided threshold value is not proper, an error signal is sent to the part 4. Then a control part 12 delivers the data on the coordinate value of a desired pattern and the number of coordinates to the outside.