Inbetweening with occlusions for non-linear rough 2D animation

Abstract

Representing 3D motion and depth through 2D animated drawings is a notoriously difficult task, requiring time and expertise when done by hand. Artists must pay particular attention to occlusions and how they evolve through time, a tedious process. Computer-assisted inbetweening methods such as cut-out animation tools allow for such occlusions to be handled beforehand using a 2D rig, at the expense of flexibility and artistic expression.

In this work, we extend the more flexible 2D animation framework of Even et al., (2023) to handle occlusions. We do so by retaining three key properties of their system that are crucial to speed-up the animation process: input rough drawings, real-time preview, and non-linear animation editing. Our contribution is two-fold: a fast method to compute 2D masks from rough drawings with a semi-automatic dynamic layout system for occlusions between drawing parts; and a method to both automatically and manually control the dynamic visibility of strokes for self-occlusions. Such controls are not available in any traditional 2D animation software especially with rough drawings. Our system helps artists produce convincing 3D-like 2D animations, including head turns, foreshortening effects, out-of-plane rotations, overlapping volumes and even transparency.