BetweenIT: An Interactive Tool for Tight Inbetweening

TLDR

Generating inbetween frames that interpolate key frames is a major, time‑consuming component of 2D feature animation, especially for tight inbetweens. The study aims to cut inbetweening costs by providing an interactive environment that automates the process while allowing artists to guide or override it, focusing on high‑precision, expensive portions. We developed user‑guided semi‑automatic techniques, including a novel stroke‑interpolation method using logarithmic spiral vertex trajectories combined with curvature‑based deformation and twisting warps, to reduce artist gestures.

Abstract

Abstract The generation of inbetween frames that interpolate a given set of key frames is a major component in the production of a 2D feature animation. Our objective is to considerably reduce the cost of the inbetweening phase by offering an intuitive and effective interactive environment that automates inbetweening when possible while allowing the artist to guide, complement, or override the results. Tight inbetweens, which interpolate similar key frames, are particularly time‐consuming and tedious to draw. Therefore, we focus on automating these high‐precision and expensive portions of the process. We have designed a set of user‐guided semi‐automatic techniques that fit well with current practice and minimize the number of required artist‐gestures. We present a novel technique for stroke interpolation from only two keys which combines a stroke motion constructed from logarithmic spiral vertex trajectories with a stroke deformation based on curvature averaging and twisting warps. We discuss our system in the context of a feature animation production environment and evaluate our approach with real production data.