Smooth line-only pen drawing in Inkscape

Using pen and paper I drew a castle (monochrome, only lines, no fillings, no gradients, no pen pressure differences), then scanned it and vectorized it with Trace Bitmap in Inkscape:

enter image description here

I want to reduce the number of nodes to make the drawing look smoother and easier to edit. Here is a detail showing how not-smooth my hand-drawing is:
enter image description here

I thought Path>Simplify would work but unfortunately it simplifies too much and creates black areas that feel unnatural for a pen-drawn line drawing:

enter image description here

Is there another feature I could use, which would make the lines smoother? Ideally the tool would understand what a pen-drawn line is, and use that knowledge to maintain consistent line widths.

I use Inkscape but I can also use any other free tool available on Linux.

Answer

You could use the centerline trace extension available from here: https://github.com/fablabnbg/inkscape-centerline-trace to trace your scanned image in Inkscape.

Or you could set the simplifying threshold in the settings: Edit > Preferences > Behavior : Simplification threshold.

Inkscape centerline trace

Applied to the question’s line drawing:

enter image description here

The transformation takes about 10 seconds. As you can see, the tool understands the concept of pen lines, and does not create the kind of dark areas that Simplify generates. It makes the drawing easy to modify manually. Be sure to adjust the Median filter until you obtain a good result.

Attribution
Source : Link , Question Author : Nicolas Raoul , Answer Author : Nicolas Raoul

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