Abstract:

To them, I said, the truth would be literally nothing but the shadows of the images. - Plato, The Republic

Shadow art is a unique form of sculptural art where the 2D shadows cast by a 3D sculpture are essential for the artistic effect. We introduce computational tools for the creation of shadow art and propose a design process where the user can directly specify the desired shadows by providing a set of binary images and corresponding projection information. Since multiple shadow images often contradict each other, we present a geometric optimization that computes a 3D shadow volume whose shadows best approximate the provided input images. Our analysis shows that this optimization is essential for obtaining physically realizable 3D sculptures. The resulting shadow volume can then be modified with a set of interactive editing tools that automatically respect the often intricate shadow constraints. We demonstrate the potential of our system with a number of complex 3D shadow art sculptures that go beyond what is seen in contemporary art pieces.

Results:

(Top) Three currency symbols combined in a sculpture built from Lego. Inconsistencies are marked in light gray in the bitmap images. The relative scaling is not preserved due to the elongation of Lego bricks in one direction. The black pedestal has been added for stability.

(Left) The brush, ray, and erosion tools provide versatile editing functionality for modifying the 3D sculpture hull without altering the desired shadow images provided by the user.

(Right) Example-based shadow art. Well-known graphics models are used to create a constructive shadow art sculpture that casts three shadows at 45 degree angle depicting the Siggraph logo.

(Left) A shadow art tribute to Andy Warhol. A seemingly random voxel soup embedded into a glass cube creates three distinct shadow images.

(Top) A 3D printout of the example shown in Figure 5. Some features are lost due to restrictions of the 3D printer.

(Left) Sketch-based model creation exploits our geometric optimization to warp the input drawings towards a consistent state.

(Top) A sculpture casts three shadow poses of an animated cartoon character at 60 degree angle. Substantial initial inconsistencies (shown as gray pixels) have been removed by the optimization. The red line indicates a topological surgery performed by the user on the deformation mesh to specify the shape semantics. Bottom row shows the sculpture from different viewpoints without the transparent casing.

@article{mp_sa_siga_09,
AUTHOR = "N. J. Mitra and M. Pauly",
TITLE = "Shadow Art",
JOURNAL = "{ACM} Transactions on Graphics",
VOLUME = "28",
NUMBER = "5",
note = "to appear",
YEAR = "2009",
}