Turn Image into a Pencil Drawing - GIMP Tutorial

This basically a summary from a YouTube video that I thought was 
interesting, especially if your version of GIMP is too old to be able
to use the G'Mic-Qt plugin.

Video: https://www.youtube.com/watch?v=eLgsSN2MsMo

1. Duplicate the image layer until there are three identical layers.
2. Select the first (top) layer and turn the saturation all the way down
3. Select the first (top) layer and change the layer mode to Saturation.
4. Select the second (middle) layer and change the layer mode to Dodge.
5. Select the second (middle) layer and invert the colors
6. Select the second (middle) layer and use Gausian Blur with the 
   horizontal and vertical values set to 15 if using a medium-sized 
   image and higher if the image is large; use smaller if you have a 
   smaller image.
7. Select the third (bottom) layer and adjust the color level via
   Colors --> Levels... and adjust the Input Levels by sliding the
   first (left) triangle to the right and do the same for the last
   (right) triangle until the image looks good. Then, adjust the middle
   triangle for further editing.