Reads a portable pixmap as input. Does a Laplacian relief filter, and
writes a portable pixmap as output.
The Laplacian relief filter is described in "Beyond Photography" by
Holzmann, equation 3.19. It's a sort of edge-detection.
pgmbentley(1), pgmoil(1), ppm(5)
Copyright (C) 1990 by Wilson Bent (email@example.com)
11 January 1991 ppmrelief(1)
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