Later experiments indicated that the correlations between the light beam that hits the camera and the beam that hits the object may be explained by purely classical physics. If quantum correlations are present, the signal-to-noise ratio of the reconstructed image can be improved. In 2009 'pseudothermal ghost imaging' and 'ghost diffraction ' were demonstrated by implementing the 'computational ghost-imaging' scheme, which relaxed the need to evoke quantum correlations arguments for the pseudothermal source case.