This is an implementation of "Vectorization of Line Drawings via PolyVector Fields" by Mikhail Bessmeltsev and Justin Solomon, Massachusetts Institute of Technology, 2018. Actual coding done by Mikhail Bessmeltsev, http://www-labs.iro.umontreal.ca/~bmpix/.

USAGE: ./polyvector(.exe) filename

OUTPUT: Creates a filename.svg in the same folder.

Docker usage

1. Run docker make run
2. To launch the GUI, polyvector_thing $filename
3. To launch the CLI, polyvector_thing_cli $filename
4. The data must be placed in the sample_inputs folder, or another one must be connected

Requirements

(Other versions might also work, but these are the ones I used)

• QT 5.7 (for the version with GUI)
• OpenCV 2.4
• Boost 1.65.1
• Eigen 3.3.1

Citation

When using the code in your research work, please cite the following paper:

@article{Bessm2019,
author = {Bessmeltsev, Mikhail and Solomon, Justin},
title = {Vectorization of Line Drawings via Polyvector Fields},
journal = {ACM Trans. Graph.},
issue_date = {February 2019},
volume = {38},
number = {1},
month = jan,
year = {2019},
pages = {9:1--9:12},
articleno = {9},
numpages = {12},
publisher = {ACM},
address = {New York, NY, USA},
keywords = {Vectorization, frame field, line drawing, polyvector field},
} 

Building

1. Create folder 'build' in the same folder as this README.
2. In cmd (windows) or sh/bash (linux/mac):

build GUI app

   > cd build  
   > cmake .. -D WITH_GUI=1 -D WITH_QT=1  
   > make

build CLI qtapp

   > cd build  
   > cmake .. -D WITH_QT=1  
   > make  

build CLI app

   > cd build  
   > cmake ..
   > make  

(If you are on Windows, the last instruction will depend on the compiler you're using, e.g. 'nmake' for Visual Studio). If you want fast optimized code, replace "cmake .." by "cmake .. -D CMAKE_BUILD_TYPE=Release".

Building docker with all requirements

make build

After this simple command you will build a container that satisfies all env and is able to run the application:

polyvector_thing $filename # GUI APP
polyvector_thing_cli $filename # CLI APP
polyvector_thing_cli_qt $filename # CLI QT APP

Parameters

1. All the tunable parameters are in Params.h
2. In a couple of places in the code there are seemingly random constants like 10 - those are implementation-dependent constants and have nothing to do with algorithm parameters. Proper engineering would fix those, but before that happens - please do not change.

Notes

1. This is not the optimized version we tested for performance. The optimized version is available upon request.
2. There are a few minor changes from the paper description:
   • Section 5.2 has been reimplemented since the submission for robustness. This might have introduced minor (~2 pixel)-differences to some of the results, mostly making them better.
   • Instead of outputting a raw non-smooth vectorization with many segments, which takes a while to output, we use Douglas-Peucker algorithm and then Laplacian smoothing on the result. Douglas-Peucker does not change anything significant in the result, except for the density of the control points. Laplacian smoothing was not used for the paper results, instead we used, as we noted, Adobe Illustrator's 'Simplify' feature. Those two steps were added to immediately output a decent .svg if Illustrator is not available.

Known Issues

1. Output might contain 'nan's. Your importer/viewer should ignore those points.

Comparisons

The whole algorithm depends on the background/foreground separation, which is done via a simple intensity threshold. If you see that some lines are missing in the vectorization, that's just it. Increase the contrast of your image in some bitmap editor (Photoshop?) and rerun. Alternatively, you can adjust the threshold in the code (BACKGROUND_FOREGROUND_THRESHOLD in Params.h). So if you're comparing to our paper, please try a few contrast settings.