Pore distribution

Hi, I need to do the pore distribution of this SEM image:


I search on internet how to do, I do the image threshold and it return the following image:

The next step is set the scale, in this case 0.33 pixel/micron, then analyze particles and show the results:
Cattura1
After this in the results page I do results-distribution (parameter area) and show me this graph:

But I want a grph like this:

What should I do? It’s possible to do the distribution of pore radius?
Thanks.