Normalized and anti-aliased Z pass? In Blender Cycles a Z pass can be automatically normalized with a Normalize node.
A Mist pass is anti-aliased and have smooth shading.

How to get automatically normalized and anti-aliased depth map?

I tried the method with Ray Length input, normalizing works fine but I got an unsatisfied result with compositing — the thin gray background that I have to add to normalize the image:



The Mist pass can't be automatically normalized properly, because all the space behind the object is equal 1.



Or should I do it in the other proper way?

Thanks!
Ok, I finally solve it.
The normalized mist pass node group with and without alpha mask: