I recently saw a commercial where people were rendered like cartoons. I thought it would be a fun idea for an internet avatar. Here’s what I did to try cel-shading in GIMP:
- Pull up your picture and open the Layers window (Ctrl-L).
- Right-click in the layer window and duplicate your layer so that you have 2 copies.
- First, we work on the drawing layer on top. Run Colors->Threshold on the top layer to turn it black and white.
- Filters->Edge-Detect->Edge… Check Black and run it to generate the drawing lines.
- Colors->Invert to make the drawing lines black.
- Layer->Transparency->Color to Alpha to get rid of the white in the drawing layer.
- Now for the coloring. Click on the untouched lower layer. Colors->Posterize level 7. This limits it to seven colors.
- Optional: Use stroked paths to fill in missing drawing lines. Use Color Picker and Bucket Fill to fill in colored areas that don’t look like painting. Cut out the background with the foreground select tool. Invert the selection and delete the background. Ctrl-Z (undo) is your friend.
- If you cut out the background, you can export to a transparent .png or .gif when you’re done.