[Fx,Fy] = VL_GRAD(F) returns the finite differencies gradient of the image F. The function uses central differencies and for all but the boundaries pixels, for which it uses forward/backward differencies as appropriate.

VL_GRAD(F,'forward') uses only forward differencies (except on the lower and right boundaries, where backward difference is used). Similarly, VL_GRAD(F,'backward') uses only backward differencies.

See also: GRADIENT(), VL_HELP().