I have this confusion related to Laplacian filter. It states that it uses second derivative and finds the point of zero crossing(where the second derivative is zero) for which the first derivative has the high peak. I have seen them using kernels like
0 1 0 1 -4 1 0 1 0
I am not sure how this kernel finds the point of zero crossing. I mean definitely this kernel is equivalent to the second derivative.
Suppose I have points something like this
0 255 255 0 255 255 0 255 255
Definitely, it has an edge at the middle. But if I convolve the kernel with this image for example. I won't get zero result. So how come its called zero crossing