Question

I am using OpenCV 2.2 on MS Visual C++ 2010 on Windows 7. 32 bit application.

I am trying to make the following matrix. [-1 0 1].

I try

cv::Mat Kernel = cv::Mat::zeros(1, 3, CV_8S );

Kernel.data[0] = -1;

Kernel.data[2] = 1;

I get [255 0 1].

I get the same result regardless of what I replace CV_8S with.

Can anyone see what I am doing wrong?

Thanks,
Peter

Answer 1

the data member of cv::Mat is in fact uchar* and not char* regardless of the actual matrix type (i.e. CV_8U), I guess you print the values by iterating over kernel.data without casting data from uchar* to char* (or checking them with watch without doing the same) and that why you cant see negative number.

Additionally, you have a nicer syntax to achieve the same

cv::Mat kernel = (cv::Mat_<char>(1,3) << -1, 0, -1);