The theory that light can transmit information in a unique way has been proved by the experiment and theory of correlated imaging. In this paper, the principles of correlated imaging were discussed in semi-classical interpretations. In the view of pseudo-thermal light field, photoelectric detection and correlated computation, the imaging process was analyzed. Field of view, spatial resolution and contrast of the system were given. On this basis, the traditional linear correlation algorithm was improved to make the ghost image a mean square convergence unbiased estimation of the object transmission function. The corresponding computational ghost imaging experiment measurement indicates that under the same number, especially less than the Nyquist frequency, the PSNR is significantly improved and background noise is effectively suppressed compared with the traditional algorithm.