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Manufacturing Layered Attenuators for Multiple Prescribed Shadow Images

I. Baran, P. Keller, D. Bradley, S. Coros, W. Jarosz, D. Nowrouzezahrai, M. Gross

Proceedings of Eurographics (Cagliari, Italy, May 13-18, 2012), Computer Graphics Forum, vol. 31, no. 2, pp. 603-610

Abstract

We present a practical and inexpensive method for creating physical objects that cast different color shadow im- ages when illuminated by prescribed lighting configurations. The input to our system is a number of lighting con- figurations and corresponding desired shadow images. Our approach computes attenuation masks, which are then printed on transparent materials and stacked to form a single multi-layer attenuator. When illuminated with the input lighting configurations, this multi-layer attenuator casts the prescribed color shadow images. Alternatively, our method can compute layers so that their permutations produce different prescribed shadow images under fixed lighting. Each multi-layer attenuator is quick and inexpensive to produce, can generate multiple full-color shadows, and can be designed to respond to different types of natural or synthetic lighting setups. We illustrate the effectiveness of our multi-layer attenuators in simulation and in reality, with the sun as a light source.

Overview

In this work we describe how to construct layered attenuators, whose shadows form different images depending on the lighting configuration (Figure 1). Layered attenuators are seemingly random patterns printed on transparencies and stacked together, which, when properly illuminated, cast different color images as shadows.

Figure 1: A single manufactured multi-layer attenuator, consisting of three transparencies separated by acrylic, casts different shadows depending on the angle of the sun. The shadows match the target Van Gogh paintings, shown as insets.

Layered attenuators can make appealing art pieces. They can be incorporated into personalized memorabilia, such as keyrings, because of their low manufacturing cost and sim- plicity. An intriguing application is using a layered attenuator in place of a stained glass window to produce different images depending on the day or the time of day. Or if only a fraction of layer permutations lead to images, finding them may be an amusing puzzle.

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