Spatio-temporal analysis for parameterizing animated lines

Abstract

Figure 1: Our algorithm builds a temporally consistent parameterization for lines extracted from an animated 3D scene. AbstractWe describe a method to parameterize lines generated from animated 3D models in the context of animated line drawings. Cartoons and mechanical illustrations are popular subjects of nonphotorealistic drawings and are often generated from 3D models. Adding texture to the lines, for instance to depict brush strokes or dashed lines, enables greater expressiveness, e.g. to distinguish between visible and hidden lines. However, dynamic visibility events and the evolving shape of the lines raise issues that have been only partially explored so far. In this paper, we assume that the entire 3D animation is known ahead of time, as is typically the case for feature animations and off-line rendering. At the core of our method is a geometric formulation of the problem as a parameterization of the space-time surface swept by a 2D line during the animation. First, we build this surface by extracting lines in each frame. We demonstrate our approach with silhouette lines. Then, we locate visibility events that would create discontinuities and propagate them through time. They decompose the surface into charts with a disc topology. We parameterize each chart via a least-squares approach that reflects the specific requirements of line drawing. This step results in a texture atlas of the space-time surface which defines the parameterization for each line. We show that by adjusting a few weights in the least-squares energy, the artist can obtain an artifact-free animated motion in a variety of typical non-photorealistic styles such as painterly strokes and technical line drawing.

Vector graphics animation with time-varying topology

“…However, the 3D-to-2D conversion is typically a per-frame process and therefore does not output a time-continuous 2D animation. To address this issue, [Karsch and Hart 2011] tracks the snaxels' 3D positions in the original mesh to generate correspondences across 2D frames, [Buchholz et al 2011] computes a parameterization of the spacetime surface swept by the silhouette lines, and [Bénard et al 2012] uses an image-space relaxation method to deform, split and merge active strokes at frame i to match the feature lines of frame i + 1. Unfortunately, unlike ours, all these methods require to create a 3D animation beforehand.…”

“…Unfortunately, unlike ours, all these methods require to create a 3D animation beforehand. In addition, their output representation either does not support vectorized coloring [Buchholz et al 2011;Bénard et al 2012], or breaks the animation into contour sequences that do not change in topology [Karsch and Hart 2011]. In this paper, we present a novel representation that could be used as output of these existing methods to address their limitations.…”

Stylized strokes for coherent line drawings

“…The method in Ref. [8] needs to know the viewpoint sequence in advance, and reconstructs a parameterized space-time surface by sweeping lines during the animation. This allows the determination of changes in line topology, but at the expense of high computational cost.…”

“…Several researchers have addressed the problem of temporal continuity for stylized line drawing animations [5][6][7][8][9]. They pay particular attention to tracing the lines in order to obtain coherent parameterization for stylization.…”

Customizable Strokes for Localized Stylization of View-Dependent Lines Extracted from 3D Models

“…Recently, some researches have focused on how to propagate the parameters of the lines in order to maintain the coherence of stylized strokes as the viewpoint changes or the 3D model is animated [11], [12], [13], [14], [15].…”