Research On 3D Imaging Combing Fringe Projection And Light Field

Three-dimensional(3D)imaging technique can reconstruct the 3D digital model of real objects,which connects the real world with the digital world and has been widely used in various fields.As one of representative techniques in optical 3D imaging,fringe projection profilometry(FPP)has the advantages of non-contact,simple structure,high accuracy and high speed.Related basic theories of FPP are mature,which makes the applications of FPP gains become more and more widespread.However,when used for some specific tasks,FPP needs to be further improved in some key points,including the efficiency of data acquisition and processing,the dynamic range of imaging and the completeness of the surface data.On the other hand,as an emerging technique in the field of computational photography,light-field imaging breaks through the limitation of traditional camera.It can obtain the four-dimensional(4D)light field data containing positions and directions simultaneously,which provides inspiration to develop new approaches of optical 3D measurement.This thesis first briefly introduces representative techniques and trends of 3D imaging,and then summarizes the state-of-the-art of light field imaging.The research of the thesis focuses on light field 3D imaging and phase extraction in FPP.To overcome the dependence on surface texture in passive light field 3D imaging,an active light field 3D masurement method combing fringe proj ection is proposed,which takes full advantages of phase coding and light field respectively.To improve the efficiency of data acquisition in FPP,a two-step phase-shifting algorithm for phase retrieval is presented based on the working mechanism of FPP and its validity is proved in experiments.The main research achievements of the thesis are listed as following:Phase coding is introduced into the light field 3D imaging and the epipolar plane image(EPI)is employed to analyze the 4D light-field data coded by phase,which can reconstruct the depth of obiects.Active light field 3D measurement system is built with a light field camera and a digital projector,which can accurately measure the surface without enough texture.The equation of fringe intensity is simplified considering the working mechanism of FPP.Then a two-step phase-shifting algorithm for phase retrieval is proposed based on the simplified equation.The two solutions of phase are modeled with the intersection between a line and a circle,and the correct solution can be selected by utilizing the monotonicity of phase map.Interpolation is also employed to compensate the phase selection error arising from discrete sampling.Based on the distribution of phase error,the influence of ambient light is qualitatively discussed.Then the model of two-step phase-shifting is rectified,with which the phase error can be reduced by refining the fringe contrast.Finally,the algorithm of two-step phase-shifting is extended to be compatible to arbitrary amount of phase shifting.The experiments demonstrate the feasibility of the proposed algorithm.