Fast And Automatic Exposure And Focus Control Method Research For High-speed Camera

With the constant advancement of science and technologies,the speeds of the targets that need to be tracked by photoelectric theodolites become ever higher,and these kinds of targets often experience sharp changes in their trajectories,statuses,etc.in a very short period of time.In order to record the state of a specific moment or the target's entire moving process,modern photoelectric theodolites are usually equipped with a high-speed camera as the image acquisition device,but it is rarely to see a highspeed camera with auto exposure and auto focus facility in the market,and the conventional cameras' auto exposure and auto focus facility can't compatible with the high-speed camera.To address the above issues,a real-time and fast automatic dimming and focusing method has become a common goal in the research of photoelectric theodolites.This paper starts from an image processing method based on digital signals,studies the characteristics of the high-speed cameras adopted by photoelectric theodolites,and comes up with an automatic and fast dimming and focusing method applicable to the high-speed cameras of photoelectric theodolites.Major contribution to the workFirst,for research of the automatic dimming method,this paper firstly establishes a mathematic model based on the influence of illumination intensity on the camera,and by analyzing the occurring mechanism of the camera's overexposure and underexposure and the illumination conditions the high-speed camera of a photoelectric theodolite needs to cope with,puts forward an image brightness evaluation method based on image histogram feature function.Compared with conventional dim-ing methods,this method delivers better results under front lighting and backlighting conditions which feature wide illumination intensity fluctuations,and the function's calculate consume time is within 0.2ms.To further improve the function's real time performance,conducts research on the hardware acceleration performance of the function,the experiment provided that the GPUS acceleration have a significant superiority when the image have a lager resolution.Second,the paper comes up with an automatic dimming method which integrates both coarse and fine exposure tunings.In coarse tuning,sharp adjustment is performed to the electronic shutter so as to quickly bring the camera out of overexposure or underexposure;in fine tuning,fixed-step-size and variable-step-size hill climbing methods are combined to perform search approximation for the optimal exposure value.Besides,the paper also,through a static experiment,verifies that the method presented boasts better adaptability under conditions featuring sharp and wide illumination intensity changes,compared with conventional methods.within 0 to 110 ms,when light intensity of the light source repeatedly changes between 760 lux and 23100 lux,the image information entropy obtained by this method is increased by 2.648,and the variance is reduced by 1.125.Third,based on the optical imaging system's mathematic model,the paper analyzes the point spread function and focus method in depth from defocus and the frequently used image quality evaluation function in depth from focus.Then it proposes an image evaluation function based on the image histogram characteristic function for auto focusing.The study shows that this function can overcome the defection where separate calculation of traditional auto-exposure and auto-focus evalutional functions will occupy system resources and lead to slow calculating speed;the study also proves that the precision and focusing range of this function can support auto focusing in highspeed cameras.Forth,based on the image histogram characteristic function,this paper presents an automatic focusing method which integrates fast focus tunings.The experiments show our method can finish the auto focus within 0.9 second as the target is far from camera about 70 motor steps,wihin 9 movements.Fifth,in order to simulate the conditions a photoelectric theodolite needs to cope with in actual operation based on the automatic dimming and focusing methods put forward in this paper,the last part of the paper expounds on the method and process of integrating the dimming and focusing methods,and designs corresponding experiments to verify the method for the purpose of providing reference for practical applications.Furthermore,the paper summarizes the work in this paper,and find out that there is still some work to be done and the possible direction is presented.