Polarization and Phase-shifting for 3D Scanning of Translucent Objects

Tongbo Chen, Hendrik P. A. Lensch, Christian Fuchs, Hans-Peter Seidel

MPI Informatik

Oral Presentation at CVPR 2007.

Abstract

Translucent objects pose a difcult problem for traditional structured light 3D scanning techniques. Subsurface scattering corrupts the range estimation in two ways: by drastically reducing the signal-to-noise ratio and by shifting the intensity peak beneath the surface to a point which does not coincide with the point of incidence. In this paper we analyze and compare two descattering methods in order to obtain reliable 3D coordinates for translucent objects. By using polarization-difference imaging, subsurface scattering can be ltered out because multiple scattering randomizes the polarization direction of light while the surface reectance partially keeps the polarization direction of the illumination. The descattered reectance can be used for reliable 3D reconstruction using traditional optical 3D scanning techniques, such as structured light. Phase-shifting is another effective descattering technique if the frequency of the projected pattern is sufciently high. We demonstrate the performance of these two techniques and the combination of them on scanning real-world translucent objects.


(a)	(b)	(c)

Rays to consider in 3D scanning. (a) 3D geometry can be estimated reliably only from the direct reflection at the surface. (b) The subsurface scattering in translucent objects can shift the observed peak intensity away from the point of incidence. (c) Opaque structures beneath the surface pollute the range estimate.

Our setup for polarization-difference imaging (PDI). The projector is equipped with a linear polarization filter at fixed orientation. The camera captures two image sequences with parallel and with perpendicular orientation of the polarization filters.

(a)

(b)

(c)

Combining phase-shifting and polarization our method faithfully captures the 3D geometry (b) of very translucent objects such as this alabaster Venus figurine (a) (height 19cm). For comparison, the 3D geometry obtained from a Minolta Vi-910 suffers from distortions due to subsurface scattering.

Publication:

Tongbo Chen, Hendrik P. A. Lensch, Christian Fuchs and Hans-Peter Seidel.
Polarization and Phase-shifting for 3D Scanning of Translucent Objects. In Proceedings of IEEE Conference on Computer Vision and Pattern Recognition (CVPR 2007) , Minneapolis, USA, June 2007 (oral presentation).