A displacement map does not alter the poly count of the object.

In a displacement map every pixel becomes a micro poly; displacing only the micrpoly.
You can make a displacemnt map as big as you want to obtain an infinite number of micro poly's.

Poser is NOT limited to 4096x4096 maps.
And that is 16 million micro poly's to work with..... on top of the polys already in the object to give the basic shape.

This example from the above figure shows:
Displacement mapping and smoothing and the results:

Lower feft is the origional obj file...

Clic to enlarge.

There is NO subdevision here; The initial object stays at 6300 Poly's.
And as you can see from the example he uses a 1024x1024 displacement map giving him something more 1 million micro poly's.

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