SMEAR: Stylized Motion Exaggeration with ARt-direction

Fig. 1.We present a method for the stylization of 3D motion using smear frames.From left to right on the three central frames, we show elongated in-betweens, motion lines and multiple in-betweens.All three stylization effects are based on automatically-computed motion offsets, shown color-coded in inset figures.These effects also depend on vertex velocity in this case, to limit the stylization to fast moving parts only.Smear frames are routinely used by artists for the expressive depiction of motion in animations.In this paper, we present an automatic, yet artdirectable method for the generation of smear frames in 3D, with a focus on elongated in-betweens where an object is stretched along its trajectory.It takes as input a key-framed animation of a 3D mesh, and outputs a deformed version of this mesh for each frame of the animation, while providing for artistic refinement at the end of the animation process and prior to rendering.Our approach works in two steps.We first compute spatially and temporally coherent motion offsets that describe to which extent parts of the input mesh should be leading in front or trailing behind.We then describe a framework to stylize these motion offsets in order to produce elongated in-betweens at interactive rates, which we extend to the other two common smear frame effects: multiple in-betweens and motion lines.Novice users may rely on preset stylization functions for fast and easy prototyping, while more complex custom-made stylization functions may be designed by experienced artists through our geometry node implementation in Blender.