Authors
Wan-Chun Ma, Tim Hawkins, Pieter Peers, Charles-Felix Chabert, Malte Weiss, Paul Debevec
University of Southern California Institute for Creative Technologies
Portals
Summary
In this work we present a new reflectance acquisition technique that uses a small set of lighting conditions, but is able to acquire independent estimates of diffuse and specular reflectance behavior across the entire object surface. The technique uses four spherical gradient illumination patterns which effectively compute the centroid and total energy of each pixel’s reflectance function, i.e. the amount of light reflected toward the camera as the object is lit from each direction on the sphere. We further show that the gradient patterns can be polarized, using either linear or circular polarization, in a way that the diffuse and specular components can be characterized independently. We show that the centroids of the diffuse and specular reflectance each yield an estimate of the pixel’s surface normal, and we refer to these estimates as the diffuse normals and specular normals for the object.
Abstract
We estimate surface normal maps of an object from either its diffuse or specular reflectance using four spherical gradient illumination patterns. In contrast to traditional photometric stereo, the spherical patterns allow normals to be estimated simultaneously from any number of viewpoints. We present two polarized lighting techniques that allow the diffuse and specular normal maps of an object to be measured independently. For scattering materials, we show that the specular normal maps yield the best record of detailed surface shape while the diffuse normals deviate from the true surface normal due to subsurface scattering, and that this effect is dependent on wavelength. We show several applications of this acquisition technique. First, we capture normal maps of a facial performance simultaneously from several viewing positions using time-multiplexed illumination. Second, we show that highresolution normal maps based on the specular component can be used with structured light 3D scanning to quickly acquire high-resolution facial surface geometry using off-the-shelf digital still cameras. Finally, we present a realtime shading model that uses independently estimated normal maps for the specular and diffuse color channels to reproduce some of the perceptually important effects of subsurface scattering.
Contribution
- The use of a set of view-independent spherical gradient illumination patterns to recover photometric normal maps of objects based on either diffuse or specular reflectance
- The use of linear or circular polarization patterns to separate specular and diffuse reflection under spherical illumination. This enables independent estimation of diffuse normal maps per color channel and a specular normal map, in addition to specular intensity and diffuse albedo
- Rendering with independently recovered diffuse and specular normal maps, allowing detailed surface reflection and an approximation of translucent diffuse reflectance to be rendered with a local shading model
- A novel scanning system that uses these techniques in conjunction with structured light to recover high resolution surface geometry and aligned diffuse albedo and specular intensity maps
Related Works
Reflectance Scanning Techniques; Photometric Stereo and Extensions; Polarization-Based Analysis of Reflected Light