Automatic Exposure Technology Research For Airborne Visible Light Camera

When the airborne optoelectronic platform camera system carrying out recon -naissance and measure missions , incident intensity ranges in a wide area because of the differences in season, weather, solar angle and scene.So automatic exposure is necessray to get sharp images.The traditional automatic exposure control methods basically can be described as follows:get the mean value,peak value or rms value of CCD signal through correspon- ing hardware as feedback signal,then compare feedback signal to reference signal ,in the end control the iris and exposure time according to the comparative result.But sometimes the feedback signal can't reflect the scene luminance that it can't exposure correctly .In extremes ,the system may oscillate.With the rapid development of image processing technology ,it is a trend to comb- ine automatic exposure technology with image processing technology because it's more convenient as we can run kinds of algorithms based on the same hardware,what's more,the feedback signal extracted by this method can reflect the scene luminance more accurately ,so automatic exposure technology based on image processing technology has been researched in this paper.Firstly,this paper has given an introduction of the system's principle, functional block diagram , functional module and workflow. Secondly, a real-time image grab- bing system based on TMS320DM642 has been designed. DM642 use its IIC bus to initial the video input processor SAA7113H and store images in external extended memory .Thirdly a CCD and motor control module based on C8051F020 and CPLD has been designed. C8051F020 is used to receive data from image grabbing system. CPLD is used to generate timing sequence for CCD and PWM for motor.After the hardware design, this paper has studied some existing methods and proposed a new method based on object area, a lot of experiments have been done and testified that object area method is satisfactory.