high spatial-resolution photocurrents [@Valencia2005; @Ferri2005]. Later, the theories of SPDC and pseudothermal ghost imaging were united in a Gaussian-state treatment that showed, in both cases, that ghost-image formation by photocurrent correlation arises from classical coherence propagation, but the nonclassical SPDC source offers much higher image contrast and a modest spatial-resolution advantage in near-field operation [@Erkmen2008Unified; @Erkmen2009SNR; @Erkmen2010AOP].

Recently, a computational ghost-imaging method was introduced, in which the need for a reference beam is removed [@Shapiro2008Comp; @Bromberg2009]. Conventional ghost imaging relies on the intensity cross-correlation between the signal beam on the target and the reference beam on the high spatial-resolution detector. In SPDC and pseudothermal ghost imaging, these beam patterns are random. If, however, a spatial light modulator is used to impart a sequence of known spatial patterns to a laser beam prior to propagation to the target, then diffraction theory can be used to calculate noiseless versions of the associated reference-beam intensity patterns. These computed reference-beam results can be employed, for cross-correlation ghost-image formation, as if they came from photodetection of a physical reference beam. More importantly, computational ghost imaging opens the door for more advanced computational image reconstruction techniques, notably compressive sensing [@Katz2009].

All of the preceding discussion has 