Various techniques are used to determine reflectance properties of physical objects. Such reflectance properties can be used to provide photorealistic 2 dimensional (2D) and 3 dimensional (3D) renderings of the objects and for a variety of other purposes. For example, the reflectance properties of an object can specify the color of a portion of an object for different lighting conditions in which light strikes the surfaces of the object from different directions and for various viewing angles. Existing techniques used to determine reflectance properties of physical objects generally involve taking pictures of an object from different, known camera and light directions and using the information in the captured images to compute the reflectance properties of the object. These captured reflectance properties can be modeled as a bi-directional reflectance distribution function (BRDF). A BRDF provides a way to lookup or otherwise determine what the color of each pixel of a 2D or 3D representation of the object is for given light and camera directions.
Existing devices used to capture images of physical objects to determine reflectance properties of the objects have several limitations and are especially ill-suited for capturing the reflectance properties of objects that include spatially-varying materials. A spatially-varying material is a material that changes appearance depending on the viewer's viewing direction and the direction that light strikes the material. For example, the apparent color of gold leaf material changes depending on the angle from which the viewer looks at it and from where the light is coming. Looking at a surface of gold leaf, the surface will appear to have different colors in different places on the surface due to this characteristic. Some existing devices used to capture images of an object to determine reflectance properties use a dome structure with approximately 20 lights in different positions on the inside of the dome along with a camera to capture images of the object given light from each of the lights. The limited number of lights and limited range of movement of these devices significantly reduces the resolution and accuracy of the reflectance properties that the devices can capture. The number of lights is limited based on the significant expense of positioning lights on a dome structure as well as the complexity of controlling the lights individually in such a structure. Generally, existing devices and techniques do not provide a sufficiently precise and cost effective way to capture reflectance properties of physical objects, especially those that include spatially-varying materials with rapidly changing angular dependence on view angle or lighting.