C++/GIMP/OpenCV

[Ofnuts]

• Filters > Enhance > Unsharp mask is a "classic" Gimp 2.8 plugin.
  
• `Filters enhance > Sharpen (unsharp mask) is the new GEGL-based version
  

They have the same parameters so which one are we talking about?

The GEGL one uses GEGL-isms and is probably not easy to convert to C++. The "classic" version uses convolution kernels so once you know how to convert the inputs to the adequate kernels you should be in business.

A completely different option is to try with sharpening options in OpenCV and see which one gives equivalent results (there is an unsharpMask operation in OpenCV).