Figure 2: Stages of 3D structure and reflectivity reconstruction algorithm.

(a) Raw time-tagged photon-detection data are captured using the SPAD camera set-up. Averaged over the scene, the number of detected signal photons per pixel was ∼1, as was the average number of background-light detections plus dark counts. (b) Step 1: raw time-tagged photon detections are used to accurately estimate the scene’s reflectivity by solving a regularized optimization problem. (c) Step 2: to estimate 3D structure, extraneous (background light plus dark count) photon detections are first censored, based on the longitudinal sparsity constraint of natural scenes, by solving a sparse deconvolution problem. (d) Step 3: the uncensored (presumed to be signal) photon detections are used for 3D structure reconstruction by solving a regularized optimization problem.