  We study the influence rules of the speckle size of light source on ghost
imaging, and propose a new type of speckle patterns to improve the quality of
ghost imaging. The results show that the image quality will first increase and
then decrease with the increase of the speckle size, and there is an optimal
speckle size for a specific object. Moreover, by using the random distribution
of speckle positions, a new type of displacement speckle patterns is designed,
and the imaging quality is better than that of the random speckle patterns.
These results are of great significances for finding the best speckle patterns
suitable for detecting targets, which further promotes the practical
applications of ghost imaging.
