Canny Edge Detection

void Canny(InputArray image, OutputArray edges, double threshold1, double threshold2, int apertureSize=3, bool L2gradient=false )
Parameters:

• image – single-channel 8-bit input image.
• edges – output edge map; it has the same size and type as image .
• threshold1 – first threshold for the hysteresis procedure.
• threshold2 – second threshold for the hysteresis procedure.
• apertureSize – aperture size for the Sobel() operator.
• L2gradient – a flag, indicating whether a more accurate norm should be used to calculate the image gradient magnitude ( L2gradient=true ), or whether the default norm is enough ( L2gradient=false ).

 A good example for Canny Edge Detection is provided in OpenCV Documentation..

Functions:

Canny, cvtColor, imshow, imread, namedWindow, waitKey.

Example:

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#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "iostream"

using namespace cv;
using namespace std;

int main( )
{
    Mat src1;
    src1 = imread("lena.jpg", CV_LOAD_IMAGE_COLOR);
    namedWindow( "Original image", CV_WINDOW_AUTOSIZE );
    imshow( "Original image", src1 );

    Mat gray, edge, draw;
    cvtColor(src1, gray, CV_BGR2GRAY);

    Canny( gray, edge, 50, 150, 3);

    edge.convertTo(draw, CV_8U);
    namedWindow("image", CV_WINDOW_AUTOSIZE);
    imshow("image", draw);

    waitKey(0);                                       
    return 0;
} 

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Result: