Fiji image processing: curvature in photomicrograph

Dear Sir or Madam,
Dear colleagues,

I am investigating the curvature of fibre bundles in a specimen produced out of carbon fibre reinforced plastic. The curved fibre bundle itself lies in a curved specimen (a segment of a tube cut under 45° to its rotational axis). I attached a typical photomicrograph and an edited picture that shows what I am interested in. The aim of my work is to receive either the (more or less) exact curvature of the fibre bundle. Or at least a possibility to “insert” points whose (pixel-exact) coordinates I can export and later on set up a polynominal function through these points.

Do you have any suggestions on how to get the curvature of the fibre bundles?

I am looking forward to hearing from you and thank you for all constructive suggestions.
Best regards,
Felix