  Quanta Image Sensor (QIS) is a single-photon detector designed for extremely
low light imaging conditions. Majority of the existing QIS prototypes are
monochrome based on single-photon avalanche diodes (SPAD). Passive color
imaging has not been demonstrated with single-photon detectors due to the
intrinsic difficulty of shrinking the pixel size and increasing the spatial
resolution while maintaining acceptable intra-pixel cross-talk. In this paper,
we present image reconstruction of the first color QIS with a resolution of
$1024 \times 1024$ pixels, supporting both single-bit and multi-bit photon
counting capability. Our color image reconstruction is enabled by a customized
joint demosaicing-denoising algorithm, leveraging truncated Poisson statistics
and variance stabilizing transforms. Experimental results of the new sensor and
algorithm demonstrate superior color imaging performance for very low-light
conditions with a mean exposure of as low as a few photons per pixel in both
real and simulated images.
