SmoothSketch

Abstract

We introduce SmoothSketch---a system for inferring plausible 3D free-form shapes from visible-contour sketches. In our system, a user's sketch need not be a simple closed curve as in Igarashi's Teddy [1999], but may have cusps and T-junctions, i.e., endpoints of hidden parts of the contour. We follow a process suggested by Williams [1994] for inferring a smooth solid shape from its visible contours: completion of hidden contours, topological shape reconstruction, and smoothly embedding the shape via relaxation. Our main contribution is a practical method to go from a contour drawing to a fairly smooth surface with that drawing as its visible contour. In doing so, we make several technical contributions: • extending Williams' and Mumford's work [Mumford 1994] on figural completion of hidden contours containing T-junctions to contours containing cusps as well, • characterizing a class of visible-contour drawings for which inflation can be proved possible, • finding a topological embedding of the combinatorial surface that Williams creates from the figural completion, and • creating a fairly smooth solid shape by smoothing the topological embedding using a mass-spring system.We handle many kinds of drawings (including objects with holes), and the generated shapes are plausible interpretations of the sketches. The method can be incorporated into any sketch-based free-form modeling interface like Teddy.

Structuring and layering contour drawings of organic shapes

“…Comparison with previous work: The closest work we can compare with is SmoothSketch [Karpenko and Hughes 2006]. While they look for a plausible completion of the hidden contour hinted by cusps, we instead use the facing contour to smoothly wrap a curve around the hypothetical 3D shape as shown in Figure 16.…”

“…Note that this definition is slightly different from the one found in the literature, since our term is in between the concepts of suggestive contours [DeCarlo et al 2003] and of cusps [Karpenko and Hughes 2006], to better match what we observed in typical line drawings. Decorative elements: These include all curves in D that are not visible contours of the depicted shape, but can instead represent ornamental details, 1D elements such as hair, or strokes used to represent bas-relief carvings.…”

“…This new goal brings us to prior work in the area of sketch-based modeling, where a number of methods relied on the analysis of complex sketches to infer a 3D shape or a 2.5D high relief from a single sketch, e.g., [Cordier and Seo 2007;Karpenko and Hughes 2006;Xu et al 2014;Yeh et al 2017]. Most methods in the area built on a priori knowledge (or contextual information) in order to resolve ambiguities -such as requiring exact symmetric shapes [Cordier et al 2011], being restricted to garments [Turquin et al 2007] or to side views of animals [Entem et al 2014] or requesting 3D information such as a 3D skeleton from the user [Bessmeltsev et al 2015].…”

“…smooth 3D solids) depicting all visible silhouettes including cusps was tackled by Karpenko's pioneering work [Karpenko and Hughes 2006] in the context of 3D modeling from a sketch. To this end, drawn lines were represented as networks of oriented curves, enabling the authors to identify holes and to propose a reconstruction method for hidden silhouettes indicated by T-junctions.…”

“…As in Smoothsketch [Karpenko and Hughes 2006], our algorithm is designed to handle contour-drawings of smooth, closed shapes, which we refer to as organic shapes. However, to be able to handle a larger category of drawings, we also allow them to include specific categories of decorative curves such as those often used in cartoon drawing.…”