cv::Canny

imgproc.hpp

@param image 8-bit input image.

@param edges output edge map; single channels 8-bit image, which has the same size as image .

@param threshold1 first threshold for the hysteresis procedure.

@param threshold2 second threshold for the hysteresis procedure.

@param apertureSize aperture size for the Sobel operator.

@param L2gradient a flag, indicating whether a more accurate \f$L_2\f$ norm

\f$=\sqrt{(dI/dx)^2 + (dI/dy)^2}\f$ should be used to calculate the image gradient magnitude (

L2gradient=true ), or whether the default \f$L_1\f$ norm \f$=|dI/dx|+|dI/dy|\f$ is enough (

L2gradient=false ).cv::

 */

CV_EXPORTS_W void Canny( InputArray image, OutputArray edges,

                         double threshold1, double threshold2,

                         int apertureSize = 3, bool L2gradient = false );

example

cv::Canny(src, edge, 40, 100, 3);

http://docs.opencv.org/3.2.0/da/d5c/tutorial_canny_detector.html