FLAW INSPECTION METHOD FOR STEEL PLATE

PURPOSE:To allow the detection of slight and serious flaws and determination of the longitudinal pitch of flaw by connecting a serious flaw detecting circuit having a texture treating function in parallel with a slight flaw detecting circuit and a pitch determining circuit. CONSTITUTION:Surface of a steel plate 2 is scanned with a laser light in the lateral direction and a reflected light is received 3 and sent to a slight flaw detecting circuit A. Signals outputted after gray level conversion are processed by one filter selected by performing differentiation in X, Y and XY directions. The number of pixels in an outputted signal higher than a threshold value is then calculated and a signal representative of slight flaw is outputted when the number of pixels exceeds a predetermined value. On the other hand, a pitch determining circuit analyzes the longitudinal pitch of flaw and detects slight flaw and continuous flaw. A serious flaw detecting circuit B erases a texture signal and following signals on the screen of an image monitor and outputs a signal representative of serious flaw when the number of amplified signals higher than a threshold value exceeds a predetermined value. This method prevents the overdetection of slight flaw and missing of serious flaw at the time of preventing overdetection.