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Joint Stroke Tracing and Correspondence for 2D Animation - TOG & SIGGRAPH 2024

[Paper] | [Project Page]

This code is used for producing stroke tracing and correspondence results, which can be imported into an inbetweening product named CACANi for making 2D animations.

Outline

Dependencies

Quick Start

Model Preparation

Download the models here, and place them in this file structure:

models/
    quickdraw-perceptual.pth
    point_matching_model/
        sketch_correspondence_50000.pkl
        transform_module/
            sketch_transform_30000.pkl
    stroke_tracing_model/
        sketch_tracing_30000.pkl

Create Reference Vector Frames with Krita

Our method takes as inputs consecutive raster keyframes and a single vector drawing from the starting keyframe, and then generates vector images for the remaining keyframes with one-to-one stroke correspondence. So we have to create the vector image for the reference frame here.

Note: We provide several examples for testing in directory sample_inputs/. If you use them, you can skip step-1 and step-2 below and execute step-3 directly.

  1. Our method takes squared images as input, so please preprocess the images first using tools/image_squaring.py:
python3 tools/image_squaring.py --file path/to/the/image.png
  1. Follow tutorial here to make vector frames as a reference in svg format with Krita.
  2. Place the svg files in sample_inputs/*/svg/. Then, convert them into npz format using tools/svg_to_npz.py:
cd tools/
python3 svg_to_npz.py --database ../sample_inputs/rough/ --reference 23-0.png

Execute the Main Code

Perform joint stroke tracing and correspondence using sketch_tracing_inference.py. We provide several examples for testing in directory sample_inputs/.

python3 sketch_tracing_inference.py --dataset_base sample_inputs --data_type rough --img_seq 23-0.png 23-1.png 23-2.png
  • --data_type: specify the image type with clean or rough.
  • --img_seq: specify the animation frames here. The first one should be the reference frame.
  • The results are placed in outputs/inference/*. Inside this folder:
    • raster/ stores rendered line drawings of the target vector frames.
    • rgb/ stores visualization (with target images underneath) of the vector stroke correspondence to the reference frame.
    • rgb-wo-bg/ stores visualization without target images underneath.
    • parameter/ stores vector stroke parameters.

Create Inbetweening and Animation with CACANi

  1. Convert the output npz file (vector stroke parameters) into svg format using tools/npz_to_svg.py:
cd tools/
python3 npz_to_svg.py --database_input ../sample_inputs/ --database_output ../outputs/inference/ --data_type rough --file_names 23-1.png 23-2.png
  • The results are placed in outputs/inference/*/svg. There are two kinds of results:
    • chain/: the svg files store stroke chains, defining each path as a chain.
    • separate/: the svg files store separated strokes, defining each path as a single stroke. Note that the automatic inbetweening in CACANi relies on this format.
  1. Follow tutorial here to generate inbetweening and 2D animation with CACANi.

More Tools

  • tools/vis_difference.py: visualize difference between the reference image and the target one. The results are placed in sample_inputs/*/raster_diff/
cd tools/
python3 vis_difference.py --database_input ../sample_inputs --data_type rough --reference_image 23-0.png --target_image 23-1.png

Vector Stroke Correspondence Dataset

We collect a dataset for training with 10k+ pairs of raster frames and their vector drawings with stroke correspondence. Please download it here. We provide a reference code dataset_utils/tuberlin_dataset_util.py showing how to use the data.


Citation

If you use the code and models please cite:

@article{mo2024joint,
  title={Joint Stroke Tracing and Correspondence for 2D Animation},
  author={Mo, Haoran and Gao, Chengying and Wang, Ruomei},
  journal={ACM Transactions on Graphics},
  year={2024},
  publisher={ACM New York, NY}
}