Sobel Edge Detection

void Sobel(InputArray src, OutputArray dst, int ddepth, int dx, int dy, int ksize=3, double scale=1, double delta=0, int borderType=BORDER_DEFAULT )

Parameters:

• src – input image.
• dst – output image of the same size and the same number of channels as src .
• ddepth –

  output image depth; the following combinations of src.depth() and ddepth are supported:

  • src.depth() = CV_8U, ddepth = -1/CV_16S/CV_32F/CV_64F
  • src.depth() = CV_16U/CV_16S, ddepth = -1/CV_32F/CV_64F
  • src.depth() = CV_32F, ddepth = -1/CV_32F/CV_64F
  • src.depth() = CV_64F, ddepth = -1/CV_64F

  when ddepth=-1, the destination image will have the same depth as the source; in the case of 8-bit input images it will result in truncated derivatives.
  
• xorder – order of the derivative x.
• yorder – order of the derivative y.
• ksize – size of the extended Sobel kernel; it must be 1, 3, 5, or 7.
• scale – optional scale factor for the computed derivative values; by default, no scaling is applied (see getDerivKernels() for details).
• delta – optional delta value that is added to the results prior to storing them in dst.
• borderType – pixel extrapolation method (see borderInterpolate() for details).

Functions:

Sobel, Vec3b, convertTo, imshow, imread, namedWindow, waitKey.

 

This is a code from OpenCV documentation. I have made some changes to it.

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 grey;
    cvtColor(src1, grey, CV_BGR2GRAY);

    Mat sobelx;
    Sobel(grey, sobelx, CV_32F, 1, 0);

    double minVal, maxVal;
    minMaxLoc(sobelx, &minVal, &maxVal); //find minimum and maximum intensities
    cout << "minVal : " << minVal << endl << "maxVal : " << maxVal << endl;

    Mat draw;
    sobelx.convertTo(draw, CV_8U, 255.0/(maxVal - minVal), -minVal * 255.0/(maxVal - minVal));

    namedWindow("image", CV_WINDOW_AUTOSIZE);
    imshow("image", draw);

    waitKey(0);                                        
    return 0;
} 

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Result: