您可以找到图像的x导数，然后是y导数.

You can find x derivative of image, then y derivative.

Sobel(Img,gxx,CV_32FC1,1,0); //  x derivative
Sobel(Img,gyy,CV_32FC1,0,1); //  y derivative

在那之后找到阶段 http://docs.opencv.org/modules/core/doc/Operations_on_arrays.html#phase

phase(gxx,gyy,angles,inDegrees);