According to the special structure of the large visual field CCD camera used in moving target tacking

a new method based on adjusting the electronic shutter steplessly is proposed to get the high quality image. Through adjusting the exposal time in real time

we could make the light adjusting fast and accurately. To draw the gray scale of the image

this paper put forward a new method named the gray scale weighting of different regional. Since the large visual field CCD camera has a lot of background image data

it will bring much influence to the auto light control. The new gray scale drawing method which is advanced in writing could eliminate the influence. Using the RAM of FPGA

the system ensured that the light-adjusting arithmetic could work in real time by the ping-pang buffer usage strategy. The radiation scale and the result of location experiment indicated that the method could offer best image quality when the radiant luminance is from 25 W/m

2

sr to 260 W/m

2

sr.The dynamic range of the new system had increased 20 times compared with that of the system without the auto light control. The new method satisfied not only the requirment of the wide dynamic range

but also the fast speed

the real-time

and the good adaptability.