How to find the intensity Gradient in Canny Edge detector

I am implementing the cvCan开发者_如何学JAVAny in OpenCV. after using cvCanny to an image, i want to find the intensity gradient of the edges so that i can reject weaker edges by applying the threshold. how can i find the intensity gradient?

For each white pixel of the Canny image check the corresponding gradient intensity in the Sobel edge images (the gradient magnitude = sqrt(dx*dx + dy*dy)).