Freeform Image

Thomas Schiwietz, Joachim Georgii, Rüdiger Westermann
Computer Graphics and Visualization Group, Technische Universität München, Germany

Background

In this paper we present a technique for image deformation in which the user is given flexible control over what kind of deformation to perform. Freeform image extends available image deformation techniques in that it provides a palette of intuitive tools including interactive object segmentation, stiffness editing and force-based controls to achieve both a natural look and realistic animations of deforming parts. The model underlying our approach is physics-based and it is amenable to a variety of different kinds of image manipulations ranging from as-rigid-as-possible to fully elastic deformations. We have developed a multigrid solver for quadrangular finite elements, which achieves real-time performance for high resolution pixel grids. On recent CPUs this solver can handle about 16K co-rotated finite elements at roughly 60 ms.

Modified material laws: Images (b) and (c) show the difference between Hooke’s law and the rigid law if the castle is stretched vertically. Images (d) and (e) demonstrate the effects of reducing the amount of shearing (d) and rotation (e) while the castle is dragged to the right.