Passive Inter-Photon Imaging

TL;DR

This paper introduces a novel imaging method using inter-photon timing with single-photon sensors to achieve high dynamic range imaging, overcoming limitations of traditional cameras under extreme lighting conditions.

Contribution

It develops theory and algorithms for scene brightness estimation based on inter-photon timing, enabling imaging over a dynamic range exceeding ten million to one.

Findings

Achieved imaging with over ten million to one dynamic range.

Demonstrated effective scene brightness estimation using inter-photon timing.

Showcased potential applications across various fields like astronomy and biomedical 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 inter-photon timing, defined as the time delay between detection of successive photons. Based on the statistics of inter-photon 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.