Question

I was implementing a simple laplacian filter for an image processing project i was working on. I read that the mask for a 3×3 filter is:

+0 -1 +0
-1 +5 -1
+0 -1 +0

but i was wondering about the 5×5 mask.. is it:

+0 +0 +1 +0 +0
+0 +0 +1 +0 +0
+1 +1 +9 +1 +1    << like a plus (+) sign
+0 +0 +1 +0 +0
+0 +0 +1 +0 +0

OR:

+0 +0 +1 +0 +0
+0 +1 +1 +1 +0
+1 +1 13 +1 +1    << like a circle
+0 +1 +1 +1 +0
+0 +0 +1 +0 +0

thanks for your help

Answer 1

Using Mathematica, I obtained the following for the Laplacian and the Laplacian of Gaussian kernels (the latter will be less sensitive to noise). Depending on your application, it may be safe to multiply these masks by an arbitrary positive number. Note that the sum of the coefficients is 0.