2014 Reports

Phasor Imaging: A Generalization of Correlation-Based Time-of-Flight Imaging

Gupta, Mohit; Nayar, Shree K.; Hullin, Matthias B.; Martin, Jaime

In correlation-based time-of-flight (C-ToF) imaging systems, light sources
with temporally varying intensities illuminate the scene. Due to global illumination,
the temporally varying radiance received at the sensor is a combination
of light received along multiple paths. Recovering scene properties
(e.g., scene depths) from the received radiance requires separating these
contributions, which is challenging due to the complexity of global illumination
and the additional temporal dimension of the radiance.
We propose phasor imaging, a framework for performing fast inverse
light transport analysis using C-ToF sensors. Phasor imaging is based on
the idea that by representing light transport quantities as phasors and light
transport events as phasor transformations, light transport analysis can be
simplified in the temporal frequency domain. We study the effect of temporal
illumination frequencies on light transport, and show that for a broad
range of scenes, global radiance (multi-path interference) vanishes for frequencies
higher than a scene-dependent threshold. We use this observation
for developing two novel scene recovery techniques. First, we presentMicro
ToF imaging, a ToF based shape recovery technique that is robust to errors
due to global illumination. Second, we present a technique for separating
the direct and global components of radiance. Both techniques require capturing
as few as 3 − 4 images and minimal computations. We demonstrate
the validity of the presented techniques via simulations and experiments
performed with our hardware prototype.