A Square Spiral?

[gwpriester]

Is there a limit to the depth and how many layers still being discernible?

The depth image is 8 bit and can contain 256 levels. In this example, the shape on the left has 6 steps, the center is 126 steps and the rectangle on the right is 256 steps.

I added an overlay of white dashes. These divide the 6 steps on the left. You should be able to see very small changes on the six shapes on the left.