Inherent relation between visibility and resolution in thermal light ghost imaging

Ghost imaging with thermal light inevitably has a noise background, which greatly decreases the visibility of the reconstructed image. In this paper we formulate a fundamental equation that the integration of the distribution of any ghost image equals a constant in relation to the coherence of the thermal light source. With this equation we strictly demonstrate that the average visibility of ghost imaging is inversely proportional to its image resolution. In the same time, this inherently inverse relation is verified by our numerical simulation and experimental results.