MR Displace

Don’t use a displace modifier, but use this material in mental ray connection slot:

Select a bitmap. Set the extrusion strength.

In renderer, turn up max displace to be equal or above your highest extrusion strength:

In common, make sure displace is not turned off:

Apply to a plane.

The results will NOT show in a viewport.

If you use a PROCEDURAL map to displace, use Explicit map channel

... and, an XYZ to UVW UVW map ...

... if you want to properly align specularity, diffuse slots, etc.

Image shown is 500 strength.