Abstract: The modern communication theory is used in the analysis of imaging systems. The object information density model is built for analogue and digital image respectively. The utility of sub pixel technology is evaluated with the increment of object information density. This model is applied in the design of linear array CCD camera, the effect of the system's modulation transfer function (MTF) and signal to noise ration (SNR) on the quality of images is studied. It is found that the image's object information density would improve with the lift of SNR, and the effect of MTF is related with object's characteristics.