The QNDE using image processing of the magnetic camera

A scan type magnetic camera was proposed to satisfy the following demands: to obtain high speed quantitative magnetic flux leakage (MFL) distribution with homogeneous lift-off by using 2-dimensionally arrayed high sensitivity magnetic sensors; to concentrate the MFL; and to ignore the residual magnetization and magnetic hysteresis by using a magnetic fluid lens. The magnetic field distribution (MFD) image obtained by using the scan type magnetic camera is inclined to the scanning direction (x-direction) because of the poles of the magnetizer. Also, the image shows a homogeneous trend relative to the x-direction, but there are small waves in the distribution in the sensor arraying direction (y-direction). The crack information in the MFD image can be extracted using image processing. The first and second derivatives of both x and y are used in this processing. These are "1st derivative of x, partial derivative B/partial derivative x", "1st derivative of y, partial derivative B/partial derivative y", "2nd derivative of x, partial derivative B-2/partial derivative x(2)", "2nd derivative of y, partial derivative B-2/partial derivative y(2)", and "2nd derivative of x and y, partial derivative B-2/partial derivative x partial derivative y." The partial derivative B/partial derivative x distribution shows the existence of the crack. Also, the crack volume can be evaluated quantitatively, regardless of the crack direction, by using partial derivative B/partial derivative x and a cross type magnetic coil.