Use of an intensity threshold to improve the visibility of ghost images produced by incoherent light

In thermal light ghost imaging, the transparent mask, located in the object arm of the optical setup, is numerically reconstructed by correlating the speckle patterns acquired by the video camera with the output of a bucket detector placed behind the mask. We show that the visibility of images can be significantly improved by discarding every speckle pattern whose bucket output falls below a certain threshold. We also demonstrate that the efficiency of the conventional method strongly decreases when the speckle statistics deviate from the negative exponential, whereas the threshold method is more robust against changes in the statistical distribution of the speckle intensity. We also provide reasonable statistical explanations for these results.