Effect of brightness on speckle contrast and human speckle perception in laser projection systems

Speckle noise is a serious problem for laser projectors because it deteriorates the image quality. The brightness of the image is one of the important parameters to determining the speckle perception. In this paper, the effect of brightness on speckle contrast is investigated using matte and silver screens for cinema. The brightness was changed by using ND filters or changing the on-and-off duty cycle of a DMD device in a digital cinema projector. It is shown that the brightness does not affect the speckle contrast measured by a CCD camera. Then, the effect of the brightness on human speckle perception is investigated. It is shown that the brightness of the image significantly affects human speckle perception. Speckle patterns created by the image with higher brightness are more noticeable than those with lower brightness when the speckle contrast measured by a camera is the same.