In study of ultraweak luminescence (wuch as bioluminescence) the weakness of luminescence or the lack of samples (photons) and the influence of system dark noise causes low SNR in photon images acquired by image intensifier. It is proposed that a photon image correlation integral method based on statistics and a photon image processing method based on correlation processing. The method accumulates photon image to get enhanced SNR grey scale image. A computer simulation method is developed to illustrate the process. This method also illustrates the SNR relation between photon image and traditional grey scale image and provides an effective way for detecting ultraweak bioluminescence.