2.4.4 Laplacian Filters

Laplacian filters are like a spatial 2nd derivative, and are sometimes also used for edge detection. Three common forms (after Adjust Auto Levels) are:

Original		0 1 0 1 -4 1 0 1 0
1 1 1 1 -8 1 1 1 1		-1 2 -1 2 -4 2 -1 2 -1

Larger kernels are possible.

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