In pseudo-thermal ghost imaging using a laser beam passing through a rotating ground glass plate, the temporal coherence is important since the intensities in both scanning and bucket detectors have to be measured within the coherence time of the beam. However, in computational ghost imaging this requirement is obviously not enforced (since the scanning detector intensity is calculated using the phase added by the spatial light modulator). I wanted to know what is the basic difference between these two approaches? Why is it that the phase fluctuations of laser (giving rise to finite coherence time) are important in conventional pseudo-thermal ghost imaging but is not important in computational ghost imaging. Any help would be wonderful. Thanks.