Research On Mechanisms And Characteristics Of Non-scanning Time-of-flight 3D Imaging Camera

The rapid development of 3D imaging technology, has been widely used in navigation, surveillance, identification and virtual reality fields, and non-scanning three-dimensional imaging system is the focus of research. Direct TOF measurement based non-scanning 3D imaging system is suitable for military applications for its long detection range, and high penetration ability into leaves, dust and other barriers. Non-scanning 3D imaging system based on indirect TOF measurement and ICCD/ CMOS sensor, for its high spatial resolution, is more suitable for robot navigation, intelligent video surveillance, studio, game control and other close range applications. ICCD-based 3D imaging system, compared with CMOS sensor technology, has high spatial resolution and high dynamic range. But it's hard to design and optimize, since quantitative analysis method is not available. To address these problems, this dissertation studied on the principle and the characteristics of indirect TOF non-scanning 3D imaging camera based on ICCD and some conclusions for reference and improved algorithms were proposed on system principles, system modeling, data processing methods and system implementations.The first part is the ranging principle of TOF system theory. The minimum relative error of various indirect TOF methods commonly used was derived from the view of camera noise and photon noise. The cosine wave-square wave method was studied: according to sampling theory, aliasing, light modulation depth, demodulation depth of the camera, the symmetry of sampling pulse, non-linear system gain and other factors which affect measurement accuracy were studied. The results showed that dynamic range and potential well capacity of the camera should be increased. Odd harmonic of cosine modulated light and nonlinearity higher than 2nd -order had impact on accuracy. Additionally, light modulation depth and system demodulation depth, as well as the symmetry of sampling pulse should be improved.The second part studied the model of TOF scannerless 3D imaging system based on ICCD. An improved ICCD noise model was proposed, and a nonlinear gain model was used. As the light was cosine modulated and the gain of image intensifiers changed over time, the model was modified in time-discrete situation.. The system was simulated in MATLAB by Monte Carlo simulation method, together with illumination model and objects 3D data. The influence of the factors on measurement accuracy was analyzed quantificationally. The results verified the conclusion in the first part of research. Additionally, it showed that small MCP gain and low impedance MCP with small time constant should be chosen. Automatic exposure control and segmented detection method were suggested for improving the measurement accuracy. The model provides the basis and support for system design and optimization.The third part, data processing methods of 3D imaging system based on SR3000 camera were studied, and a framework for data processing was presented. Calibration and distance correction technologies were introduced. A method to eliminate range ambiguity by alternating frequency, and a rapid automatic exposure control method based on the region of interest were proposed. Considering environmental factors, a data reliability analysis method and a noise filtering method based on amplitude were proposed. Kinds of mixed pixel were discussed, and an adaptive threshold filter method for the border mixed-pixel was presented. Scatter and other special conditions were also analyzed, and a method for range data analysis based on the ratio of offset and amplitude was suggested.The last part talked about the design and optimization of non-scanning 3D imaging system. A method for system design and optimization was proposed:Firstly, the impact of parameters on the measurement results was derived, and then, the parameters were determined conversely according to the specific device performance. Finally, the parameters were corrected according to simulation results. A method for increasing the system dynamic range by exposure time delay control was proposed. Additionally, the hardware structure, software structure and structure design method were discussed.Finally the conclusion and perspective are given at the end of the dissertation.