SIGNAL PROCESSING METHOD FOR CRACK DETECTION ON SURFACE OF HEAT STEEL STOCK

PURPOSE:To increase the detection factor of cracks and at the same time reduce the factor of misdetection, by discriminating the harmful cracks from the correlation between the height and width of a signal that is calculated from the video signal of a heat steel stock. CONSTITUTION:A radiation image of a read-out slab 3 is caught by a CCD camera 6, and a video signal VS1 is sent to a bright part immobile binary coding circuit 18 of a crack detecting circuit 17 via an A/D converter 14 and a memory 15. While the output signal of the converter 14 is branched to be sent to a reference pattern detector 16. Then a reference pattern signal NS is sent to the circuit 18. A deviation signal is obtained at the circuit 18 from a delayed video signal VS and the signal NS and compared with the reference level H0, and a data signal that decides the cracks from width W and height H of the deviation signal is supplied to a relation deciding circuit 30 for the discrimination for the relations among cracks. As a result, the detection factor is increased with reduction of the misdetection factor for the cracks of the heat steel stock.