A Practical Approach to 3D Scanning in the Presence of Interreflections, Subsurface Scattering and Defocus

Global or indirect illumination effects such as interreflections and subsurface scattering severely degrade the performance of structured light-based 3D scanning. In this paper, we analyze the errors in structured light, caused by both long-range (interreflections) and short-range (subsurface scattering) indirect illumination. The errors depend on the frequency of the projected patterns, and the nature of indirect illumination. In particular, we show that long-range effects cause decoding errors for low-frequency patterns, whereas short-range effects affect high-frequency patterns. Based on this analysis, we present a practical 3D scanning system which works in the presence of a broad range of indirect illumination. First, we design binary structured light patterns that are resilient to individual indirect illumination effects using simple logical operations and tools from combinatorial mathematics. Scenes exhibiting multiple phenomena are handled by combining results from a small ensemble of such patterns. This combination also allows detecting any residual errors that are corrected by acquiring a few additional images. Our methods can be readily incorporated into existing scanning systems without significant overhead in terms of capture time or hardware. We show results for several scenes with complex shape and material properties

Novel Depth Cues from Uncalibrated Near-field Lighting

We present the first method to compute depth cues from images taken solely under uncalibrated near point lighting. A stationary scene is illuminated by a point source that is moved approximately along a line or in a plane. We observe the brightness profile at each pixel and demonstrate how to obtain three novel cues: plane-scene intersections, depth ordering and mirror symmetries. These cues are defined with respect to the line/plane in which the light source moves, and not the camera viewpoint. Plane-Scene Intersections are detected by finding those scene points that are closest to the light source path at some time instance. Depth Ordering for scenes with homogeneous BRDFs is obtained by sorting pixels according to their shortest distances from a plane containing the light source. Mirror Symmetry pairs for scenes with homogeneou

Structured Light in Scattering Media

Virtually all structured light methods assume that the scene and the sources are immersed in pure air and that light is neither scattered nor absorbed. Recently, however, structured lighting has found growing application in underwater and aerial imaging, where scattering effects cannot be ignored. In this paper, we present a comprehensive analysis of two representative methods - light stripe range scanning and photometric stereo - in the presence of scattering. For both methods, we derive physical models for the appearances of a surface immersed in a scattering medium. Based on these models, we present results on (a) the condition for object detectability in light striping and (b) the number of sources required for photometric stereo. In both cases, we demonstrate that while traditional methods fail when scattering is significant, our methods accurately recover the scene (depths, normals, albedos) as well as the properties of the medium. These results are in turn used to restore the appearances of scenes as if they were captured in clear air. Although we have focused on light striping and photometric stereo, our approach can also be extended to other methods such as grid coding, gated and active polarization imaging