BetweenIT: An Interactive Tool for Tight Inbetweening

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.

Topology-driven vectorization of clean line drawings

“…The expressiveness, efficiency, and tactile control afforded by real pencil and paper are yet to be matched by digital drawing tools, and therefore 2D animations are often still hand-drawn on paper and then scanned. The content in the resulting raster images cannot be easily edited or used with higher level algorithms that require a stroke-based vector representation, such as computer-assisted inbetweening [Whited et al 2010]. A similar problem exists even when digital drawing tools are used, since artists often build up lines with many short strokes, leading to an unorganized collection of tiny unconnected segments that are not amenable to further high-level processing.…”

“…As is, our system can be used in tandem with inbetweening techniques, such as [Whited et al 2010]. However, the vectorization quality could be improved by considering the information contained in subsequent frames, improving the decision making (Algorithm 1) and recovering from errors in the topology.…”

Vector graphics complexes

“…Therefore, as illustrated in Figure 5, two or more open edges can be connected to each others by sharing a common vertex, and manipulating this vertex would affect all incident edges. So far, this representation is identical to stroke graphs [Whited et al 2010], except that we do not order the incident edges counter-clockwise around a vertex. In addition, we define the notion of closed edge, which is an edge with no boundary vertex, as illustrated in Figure 4 (right).…”

“…Our vector graphics complex can also be seen as an extension of stroke graphs [Whited et al 2010;Noris et al 2013], that represent the topology of a drawing by nodes (our vertices) and edges. This topological information is used to establish automatic stroke correspondences between two keyframes of a traditional 2D animation, and provide topology-aware interpolation of the strokes.…”

Spatial augmented reality for physical drawing

“…Nowadays, the animation studios still have either hand-drawn animations or use computer-generated animations. The research focus on computer animation to improve interpolation between key-frames [Whited et al, 2010] and simulate plausible deformations [Sýkora et al, 2009]. In this work, we propose some ideas and a proof-of-concept implementation of tools to assist traditional animation.…”