  We establish a quantum theory of computational ghost imaging and propose
quantum projection imaging where object information can be reconstructed by
quantum statistical correlation between a certain photon number of bucket
signal and DMD random patterns. The reconstructed image can be negative or
positive depending on the chosen photon number. In particular, the vacuum state
(zero-number) projection produces a negative image with better visibility and
contrast-to-noise ratio. The experimental results of quantum projection imaging
agree well with theoretical simulations and show that, under the same
measurement condition, vacuum projection imaging is superior to conventional
and fast first-photon ghost imaging in low-light illumination.
