Passive Inter-Photon Imaging

Abstract

Digital camera pixels measure image intensities by converting incident light energy into an analog electrical current, and then digitizing it into a fixed-width binary representation. This direct measurement method, while conceptually simple, suffers from limited dynamic range and poor performance under extreme illumination -electronic noise dominates under low illumination, and pixel full-well capacity results in saturation under bright illumination. We propose a novel intensity cue based on measuring interphoton timing, defined as the time delay between detection of successive photons. Based on the statistics of interphoton times measured by a time-resolved single-photon sensor, we develop theory and algorithms for a scene brightness estimator which works over extreme dynamic range; we experimentally demonstrate imaging scenes with a dynamic range of over ten million to one. The proposed techniques, aided by the emergence of single-photon sensors such as single-photon avalanche diodes (SPADs) with picosecond timing resolution, will have implications for a wide range of imaging applications: robotics, consumer photography, astronomy, microscopy and biomedical imaging.

Comparison of super-resolution and noise reduction for passive single-photon imaging

“…27 Our method takes this idea to the extreme limit where the burst is composed of single-photon frames. 21,26…”

“…In recent papers, [19][20][21][22] the method of photon flux measurement was introduced using the timing capability of single photon-counting avalanche diodes to estimate the photon flux as the rate at which photons arrive at the detector. Equation ( 1) states the photon flux estimate, φ, over m sampled frames which is given as the reciprocal of the mean photon arrival time (t) within the m sampled frames.…”

“…These timestamps are not correlated with any active light source and are instead recorded with respect to the SPAD camera's frame start times. Although these passively acquired photon timestamps do not provide information about the 3D scene structure, by exploiting the Poisson timing statistics, it was recently shown [19][20][21][22] that these passive timestamps provide scene intensity information.…”

“…Furthermore, the timing ability of SPAD sensors was used to determine the physical intensity by estimation of the photon flux from the photon impingement rate. [19][20][21][22] In this approach, the time between photon events is determined from the mean event time. It was shown that with photon flux measurements SPAD sensors are able to perform sensing with high dynamic range.…”

Single-Photon Structured Light

“…Single-Photon imaging. Only recently have the capabilities of SPADs, operating without any temporal synchronization, been explored, with applications in high-dynamic range imaging [28,29] and burst photography [41]. Our method operates the SPAD array similar to Ma et al [41], using a sequence of binary frames.…”