| 摘要 |
PURPOSE:To suppress the variance of a threshold to detect defects accurately, by obtaining data, which follows up a texture level, from the image pickup signal of a face to be examined of a sheet material or the like by an up/down counter and inhibiting the counting during the blank period and the defect detection period. CONSTITUTION:An image pickup element 5 consisting of a CCD sensor or the like is controlled by a driving circuit 12 to scan optically the surface of an object to be examined repeatedly. A video signal VS which is outputted from the element 5 and is amplified by an amplifier 6 is compared with a threshold signal SH, which is obtained from an amplifier 15, in level by a defect discriminating comparator 16, and a binary discrimination output OUT is outputted. The output of an up/down counter 11 is given to a D/A converter 14, and the counter 11 is counted up for VS>b and is counted down for VS<b in accorddance with an output signal (c) of a comparator 7 by the output signal (b) of the converter 14, and the operation of the counter 11 is inhibited in the blank time between scannings of the element 5 and in the time when a defect is detected by the comparator 16. The signal (b) is amplified in the amplifier 15 to obtain the signal SH. |
