Diolma,

A bump map can be used as a displacement map, and for simple things, like a rock wall or a tiled roof, this normally works, but for something like an organic creature or a human, the two have seperate functions. For example, for Vincent, the bump map does the tiny skin details, like pores, small scars, beard stubble, wrinkles, etc, and the displacement map does the actual deformation of the mesh for muscle groups, face shape, etc.

Also, a bump map is a greyscale image, with no limits to the parameters, white raises the bump, black depresses it.

A displacement map is very particular, the areas where you want no displacement must be exactly 50% grey. If you do this wrong, it can slpit the seams on a mesh, which bump mapping cannot do.

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