Laplacian of Gaussian in openCV, how to find zero crossings?

Question

There is Laplacian function in openCV which directly calculate the double derivative. But this doesn't mean I will get the edges right? Because in the output there are many negative values. I go through this link and realized that after that also I had to find zero-crossings. I don't get how to find zero crossings. Can somebody help me ?

Answer 1

A zero crossing will occur when

• a value equals 0, or
• two adjacent values have opposite signs

If you have something like

Laplacian(src, dst, CV_16S);

You just need to scan dst looking for those two cases