Signed Distance Field Generation

Hi, what's my best option for producing a higher quality version of the distance node's output? I need something that oversamples the boundary between black and white.

I'm trying to create a signed distance field texture in substance designer from a threshold black and white mask generated from noise. Using the distance node and some blending, I can get something that is pretty close to what I need, but the issue is that the distance node doesn't have the capability to oversample along the boundary between black and white, and thus, it produces pixel artifacts. To illustrate the problem, here are three images.

Black and white mask:

Signed distance field remapped from [-1,1] to [0,1]

SDF visualized by normal

In the last image you can clearly see the problem with this approach. The boundary between black and white doesn't contain enough information, and so the distance node produces streaking artifacts. Simply increasing the resolution alleviates the problem somewhat, but it never truly goes away, and working in an unneccessarily high resolution is impractical.