Skeleton-Driven Inbetweening of Bitmap Character Drawings
KIRILL BRODT and MIKHAIL BESSMELTSEV, Université de Montréal, Canada
SIGGRAPH ASIA 2024

One of the primary reasons for the high cost of traditional animation is the
inbetweening process, where artists manually draw each intermediate frame
necessary for smooth motion. Making this process more efficient has been at the
core of computer graphics research for years, yet the industry has adopted very
few solutions. Most existing solutions either require vector input or resort to
tight inbetweening; often, they attempt to fully automate the process. In
industry, however, keyframes are often spaced far apart, drawn in raster
format, and contain occlusions. Moreover, inbetweening is fundamentally an
artistic process, so the artist should maintain high-level control over it.
We address these issues by proposing a novel inbetweening system for bitmap
character drawings, supporting both tight and far inbetweening.
In our setup, the artist can control motion by animating a skeleton between the
keyframe poses. Our system then performs skeleton-based deformation of the
bitmap drawings into the same pose and employs discrete optimization and deep
learning to blend the deformed images. Besides the skeleton and the two drawn
bitmap keyframes, we require very little annotation.
However, deforming drawings with occlusions is complex, as it requires a
piecewise smooth deformation field. To address this, we observe that this
deformation field is smooth when the drawing is lifted into 3D. Our system
therefore optimizes topology of a 2.5D partially layered template that we use
to lift the drawing into 3D and get the final piecewise-smooth deformaton,
effectively resolving occlusions.
We validate our system through a series of animations, qualitative and
quantitative comparisons, and user studies, demonstrating that our approach
consistently outperforms the state of the art and our results are consistent
with the viewers' perception.
cartoon inbetweening, 2D animation, mesh deformation
- [acm paper]
- [github code]
- [paper.pdf]
- [paper.zip]
- [supplementary.zip]
- [code.zip]
- [models.zip]
- [images.zip]
- [occlusion_masks.zip]
- [presentation.pptx]
@article{brodt2024inbetweening, author = {Kirill Brodt and Mikhail Bessmeltsev}, title = {Skeleton-Driven Inbetweening of Bitmap Character Drawings}, journal = {ACM Transactions on Graphics}, year = {2024}, month = {12}, volume = {43}, number = {6}, doi = {10.1145/3687955}, }
curl -L http://www-labs.iro.umontreal.ca/~bmpix/inbetweening/bibtex.bib