  Ghost imaging (GI) is an imaging technique that uses the correlation between
two light beams to reconstruct the image of an object. Conventional GI
algorithms require large memory space to store the measured data and perform
complicated offline calculations, limiting practical applications of GI. Here
we develop an instant ghost imaging (IGI) technique with a differential
algorithm and an implemented high-speed on-chip IGI hardware system. This
algorithm uses the signal between consecutive temporal measurements to reduce
the memory requirements without degradation of image quality compared with
conventional GI algorithms. The on-chip IGI system can immediately reconstruct
the image once the measurement finishes; there is no need to rely on
post-processing or offline reconstruction. This system can be developed into a
realtime imaging system. These features make IGI a faster, cheaper, and more
compact alternative to a conventional GI system and make it viable for
practical applications of GI.
