Image processing, highlighting hidden details

[nablator]

For comparison, two settings of DSTRETCH on the bottom right corner of f75r:

   

   

I doubt there is any "structure", maybe only old dirt and a more recent abrasion?

If there is an ink transfer from the opposite page there, it's hard to make out.

   

Local contrast enhanced:

   

It's not as good as my spray plaster wall for induced pareidolia.