Extracting Lines from Scanned/Photographed Drawings
Under the Filters menu, at the bottom, is "Extracting Lines..." It pops up a level-correction-style dialog, except it works rather well even on pencil art.
A little explanation guide:
But that doesn't just work on line art—it also works remarkably well on pencil art, which is difficult to get right on level correction alone:
So yes—it is entirely possible to extract lines from scanned and photographed line art without resorting to level fiddling in Photoshop/GIMP/Pixelator or paying $200+ for Clip Studio Pro EX or Corel Painter. Just download MediBang Paint Pro for free.