Vectorizing line drawings with near-constant line width

Many line drawing images are composed of lines with near-constant width. Such line width information has seldom been used in the vectorization process. In this work, we show that by enforcing the near-constant line width constraint, we are able to produce visually more pleasing vectorization results. To this end, we develop a tracing-based approach, allowing dynamic validation of the line width constraint. The key here is to derive correct tracing directions, which are determined based on an automatically estimated orientation field, shape smoothness and the near-constant line width assumption. We have examined our algorithm on a variety of line drawing images with different shape and topology complexity. We show that our solution outperforms the state-of-the-art vectorization software systems including WinTopo and Adobe Illustrator, especially at regions where multiple lines meet and thus are difficult to locally distinguish from each other.