Correspondence imaging based on correlation coefficients

In the context of correspondence ghost imaging, we utilize the correlation coefficients to separate the reference detector speckle patterns into positive and negative correlated parts. A positive image and a negative image of the object are obtained by averaging over corresponding speckle patterns. The visibility and contrast-to-noise ratio of the positive image are discussed, and it is found that the latter will reach a maximum by averaging over a little less than half of the total number of reference speckle patterns.