From Photo to Line Drawing....Without Leaving RawTherapee .

The jpg of the girl in the fur outfit has a moderate resolution: 804 by 629 pixels. While working with high resolution Raw files will generate interesting images, if you are after a line drawing medium resolution jpgs works best. That way you can view your image at 100 percent. You will be creating what would be called artifacts in a normal workflow and it is easy to go a bit too far with the sliders.

Step one

Start by upping the exposure compensation. For a realistic line drawing keep detail in at least one of the color channel in areas such as the girl's face. In other areas that will be paper white in the line drawing such as the girl's skirt you can push all channel to 100 percent,

Step two

Tone map the jpg to create edges without turning shadows into blotchy artifacts in area such as the girl's face.

Step three

If you like your original colors  this and the next step are optional. Using the three color temperature sliders produces a wide range of color shifts ranging from a total color cast to a blue tinting of the edges created in step two.

Step four

Again this step is optional.  The channel mixer switches the colors towards green.

Now another big reason for using roughly 800 pixel resolution jpgs, The bottom sliders in the contrast-by-detail tool creates hard edges. With higher resolution images the effect is nowhere as strong.

My original final image.

A water color perhaps rather than a line drawing but still an attractive image. Because of the interactions between the tools pushing beyond this didn't work out. But after I slept on the problem when I woke up I realize that if I did a second pass stating with my painterly jpg I wouldn't be fighting any interactions.

Repeating step one and two--more exposure, more tone mapping, and then setting the saturation down to -100 created this  line drawing.

Edit

Variations on a theme.

Toss in the black and white tool channel mixer and you have a ton of manipulations to play with. Here are two examples

These images were created with RawTherapee build 4.2.77. It is open source and forever free and can be downloaded at  http://rawtherapee.com/downloads