Research On Equivalent Refractive Model And Distance Measurement For Underwater Binocular Imaging

As an important branch of machine vision,underwater imaging has been widely used in marine,scientific research,exploration and other fields.However,the underwater imaging environment is more complex,and the imaging principle are quite different from that in the air.Direct application of the imaging model in the air will result in large errors,which brings severe challenges to measurement applications such as underwater binocular imaging.In this thesis,focusing on the key issues of binocular imaging ranging in water environments,it focuses on the study of underwater light propagation changes caused by refraction,exploring the mutual transformation relationship between underwater imaging models and air imaging models,and the relationship is verified by experiments.It is important for improving the measurement accuracy of underwater binocular imaging ranging and expanding its application fields in theoretical significance and potential practical value.The main work of this thesis includes:(1)Focusing on several key factors of underwater binocular imaging,the nonlinear imaging model is introduced in detail,and the conversion relationship among multiple coordinate systems such as the world coordinate system,camera coordinate system,image coordinate system,and pixel coordinate system is derived;The advantages and disadvantages of the global stereo matching algorithm and the local stereo matching algorithm in binocular imaging are summarized;the law of refraction of light in underwater imaging is discussed,and the influence of the camera on the imaging light path is analyzed at different positions in water.(2)An underwater binocular imaging simulation experiment platform is designed and built independently.Based on this platform,an underwater ranging program was formulated.A comprehensive analysis of many factors that affect camera calibration,selects the optimal calibration parameters,and uses Zhang's calibration method to calibrate the binocular camera.In order to reduce the underwater ranging error,the similarities and differences between the underwater imaging model and the air imaging model are comprehensively compared,and the influence of factors such as the focal position of the underwater camera,the thickness of the water-proof glass,and the size of the field of view on the law of light propagation is deduced.The equivalent refraction model is established,and the corresponding relationship between the underwater imaging model and the air imaging model in various situations is established,which provides the necessary theoretical support for the underwater binocular ranging experiment.(3)Experimental research on underwater binocular ranging.Aiming at the problem that the focal position of the camera is unknown in the application of this experimental platform,under the premise that the water-proof glass cannot be ignored,the situation where the focal point of the camera is located on multiple interfaces is analyzed,and the actual focal length of the camera is solved by an iterative algorithm,which further improves the actual model below the equivalent refraction model.Then,the underwater image is directly converted into the equivalent image in the air by using the equivalent refraction model,and the underwater distance measurement based on the binocular camera is realized through the SGBM algorithm and the principle of triangle similarity.Through multiple sets of multi-target ranging experiments with 202.5 mm space,the results show that the error between the measurement results and the true value is small,which is located in [-0.8 mm,1.5 mm],which illustrates the effectiveness of underwater binocular ranging.Furthermore,in view of the problem of underwater motion blur that is easy to exist in underwater imaging,the research on motion blur suppression and ranging is carried out.By changing the scale and angle of the blur kernel,the underwater motion blur image is simulated,and the influence of underwater motion blur on the binocular distance measurement is explored.The experimental results show that when the external light conditions are good and the features of the object to be measured are obvious,and the disparity map can be effectively extracted,the difference between the direct distance measurement using the blurred image and the distance measurement result after the image restoration is small.On the contrary,it is necessary to restore the blurred image to achieve underwater ranging or three-dimensional reconstruction.