  Losses should be accounted for in a complete description of quantum imaging
systems, and yet they are often treated as undesirable and largely neglected.
In conventional quantum imaging, images are built up by coincidence detection
of spatially entangled photon pairs (biphotons) transmitted through an object.
However, as real objects are non-unitary (absorptive), part of the transmitted
state contains only a single photon, which is overlooked in traditional
coincidence measurements. The single photon part has a drastically different
spatial distribution than the two-photon part. It contains information both
about the object, and, remarkably, the spatial entanglement properties of the
incident biphotons. We image the one- and two-photon parts of the transmitted
state using an electron multiplying CCD array both as a traditional camera and
as a massively parallel coincidence counting apparatus, and demonstrate
agreement with theoretical predictions. This work may prove useful for photon
number imaging and lead to techniques for entanglement characterization that do
not require coincidence measurements.
