OpenCV: How to use cvSobel? - opencv

Question

I'm trying to find the gradient direction from the edges using OpenCv 2.4.5, but I'm having problem with cvSobel() and below is the error message and my code. I read somewhere that it might be due to the conversion between floating point(??) but I have no idea on how to fix it. Any Help??
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2\opencv.hpp>
#include <opencv2\calib3d\calib3d.hpp>
#include <iostream>
#include <stdlib.h>
#include "stdio.h"
using namespace cv;
using namespace std;
int main()
{
Mat im = imread("test1.jpg");
if (im.empty()) {
cout << "Cannot load image!" << endl;
}
Mat *dx, *dy;
dx = new Mat( Mat::zeros(im.rows, im.cols, 1));
dy = new Mat( Mat::zeros(im.rows, im.cols, 1));
imshow("Image", im);
// Convert Image to gray scale
Mat im_gray;
cvtColor(im, im_gray, CV_RGB2GRAY);
imshow("Gray", im_gray);
//trying to find the direction, but gives errors here
cvSobel(&im_gray, dx, 1,0,3);
waitKey(0);
return 0;
}

Answer 1

You are mixing the C++ and C api. cv::Mat is from the C++ api and CvArr* is from the C api.
here you are using The C api cvSobel on C++ classes.
//trying to find the direction, but gives errors here
cvSobel(&im_gray, dx, 1,0,3);
What happens if you do
cv::Sobel( im_gray, dx, im_gray.depth(), 1, 0, 3);
EDIT
and declare
Mat dx;
Mat dy;
I think this might solve your problem, I'm actually quite surprised your code compiles.