This system implements the technique presented in Orientable Textures for Image-Based Pen-and-Ink Illustration
Since we were making a difference image anyway, we decided to start with something simple, a stippling effect. The following pairs of images were generated using a similar system to the line drawing system, except points are added to the difference image and final image instead of lines.
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This image was created without combing the vector field at all. If the vector field were combed to follow the curves in the painting, the final pen and ink image would look much more natural. We've discovered that combing the vector field is the most tedious, time-consuming part. Our pen and ink image of the Mona Lisa is best viewed from far.
The image at bottom was created by beginning with the image below and combing the vector field to orient the pen strokes.
