Research Of The Dimming Methods Of Photoelectric Theodolite

For a high precision optical measurement equipment, a good dimming system is of vital importance to the proper work of photoelectric theodolite; however, most of the domestic photoelectric theodolites are still using the photo resistor as the core component, which cannot accurately assess the light condition of the whole image.Therefore, the dimming system unable to work properly without the manual intervention. With the development of the third technological revolution, advances in the automatic exposure of digital camera could provide a reference for the dimming system of photoelectric theodolite.Firstly, the reasons why the dimming system cannot work properly without the manual intervention are analyzed in detail. Besides, based on the extensive research and summary on the existing auto exposure algorithms in digital camera, the drawbacks of these algorithms have been pointed out. Finally, reference to the advantage of these algorithms, a new dimming method is designed combined with the application background of photoelectric theodolite and the characteristic of its imaging system.In the scenario, the exposure body target area is firstly accessed by making full use of the function of the photoelectric theodolite tracking module. The lighting condition is also identified according to the target area lighting condition evaluation module developed in this thesis. Finally, according to different lighting conditions, different exposure evaluation algorithms are designed to assess whether the current exposure is appropriate or not; the distance between the current exposure value and the optimum amount is calculated if inappropriate, and the distance information is used as a guidance for the exposure compensation. Especially in the special lighting situation of high dynamic range, the current auto exposure algorithms of digital camera cannot work well without additional exposure compensation. In this thesis, the contrast information is merged into the ‘middle gray’ standard of digital camera to calculate optimum exposure value. In the case of back light, this method helps to enhance the brightness of target without suffering the saturate of the highlight background; and on the case of side light,due to the object itself is divided into multiple brightness levels, a contour edges based contrast algorithm which is closely related to the performance of the target detection and tracking module is developed, helps to search for the best exposure brightness for accurate dimming.In the process of rocket tracking and measurement, the brightness of flame in the tail of rocket is dazzling, while the rocket body is very dark. Especially in the low light condition, the whole image dynamic range is so wide that the dimming system unable to completely record the luminance information of the entire scene, which leads to the poor visual quality of acquired image. To solve this problem, an image enhancement scheme is presented. The proposed scheme improve the background brightness by the gamma transform, and remove the influence of ambient light by homomorphic filtering.Finally, combined the two result images, an image of flame suppression and rocket body brightness enhancement result is obtained.Finally, several tests have been carried out to verify the performance of these algorithm, the results show that the proposed exposure algorithms work better than the traditional digital auto exposure algorithms in the special light conditions, and the image visual effects have been improved to some extent by the image enhancement scheme,which facilitates the follow-up observation measurements process.