Soft shadow art

Abstract

Shadow art is a form of sculptural art in which the configuration of lights and sculptures cast 2D shadows for artistic effect. Previous computational methods for the creation of shadow art assumes a single point light that casts a bitonal shadow with sharp boundary. The goal of our study is to generate grayscale shadows using an area light (or an array of point lights) and multiple layers of occluder cells. The area light source casts soft shadows consisting of penumbra and umbra. The penumbra is the region in which only a portion of the light source is obscured by the occluders and the umbra is the region where the light sources are completely blocked by the occluders. The key challenge is to find the arrangement of the occluders such that each pixel in the shadow region gathers light from the partially occluded light source to yield a desired tone level. The problem can be formulated as combinatorial optimization with many binary variables. We present a stochastic algorithm that converges quickly to the target shadow image. Our algorithm generalizes easily to deal with arbitrary lighting and geometry setups. We demonstrate the potential of our system with a number of tonal images and the fabrication of artistic ornaments that cast grayscale shadows. © 2017 ACM.