Consistent Stereo-Assisted Absolute Phase Unwrapping Methods for Structured Light Systems

Abstract

Phase shifted sinusoidal patterns have proven to be effective in structured light systems, which typically consist of a camera and projector. They offer low decoding complexity, require as few as three projection frames per reconstruction, and are well suited for capturing dynamic scenes. In these systems, depth is reconstructed by determining the phase projected onto each pixel in the camera and establishing correspondences between camera and projector pixels. Typically, multiple periods are projected within the set of sinusoidal patterns, thus requiring phase unwrapping on the phase image before correspondences can be established. A second camera can be added to the structured light system to help with phase unwrapping. In this work, we present two consistent phase unwrapping methods for two-camera stereo structured light systems. The first method enforces viewpoint consistency by phase unwrapping in the projector domain. Loopy belief propagation is run over the graph of projector pixels to select pixel correspondences between the left and right camera that align in 3-D space and are spatially smooth in each 2-D image. The second method enforces temporal consistency by unwrapping across space and time. We combine a quality guided phase unwrapping approach with absolute phase estimates from the stereo cameras to solve for the absolute phase of connected regions. We present results for both methods to show their effectiveness on real world scenes.