The Outlines that you can draw with Synfig are formed by a rounded brush. The brush is defined by a radius that you can modify by its brush editor widget. This tutorial explains how to make brushed outlines that would improve sustantially your artwork.
What do I need to use brushes?
A brush image
Well, for the moment Synfig hasn't any brush image included so you'll need to do them by your self or grab from the free resources (insert link here to those resources).
Here are some examples of brushes (insert some brushes images here)
Brushes images are just any kind of image file that allow transparency (PNG, TIFF, GIF). More resolution your image has more big your brush size can be without pixelation. Huge file sizes would take more time to render. The balance between both options is your desition.
A recent Release
Brushes are not a primary feature of Synfig. They are obtained from the combintation of the following features:
- Duplicate Layer what implies SVN revision >= 1358
- Link to Bline (what uses the following conver types):
Strictly the Link to Bline feature is not needed but it would help on make several conversion types and linking.
The idea of brushes is to use the Duplicate layer feature with the Link to Bline (automatic or manual) feature given by the conversion types.
When you link a vertex to a bline (or a tangent or a width) it converts your parameter to the following sub-parameters.
bline "BLine" bool "Loop" real "Amount"