Research On Focused Light Field Imaging Technology And Its Application In Shape Measurement

Optical measurement is known for a high-tech combination of light,machine and electricity.Initially,it was limited to controlling and tracing the light,with less physical acquisition and less efficient systems.Having privilege of high speed,precision and noncontact characteristics,optical imaging has subverted traditional optical measurement technology in the field of measurement,bringing a revolutionary leap to optical measurement.It has been widely used in industry,biology,and Medical,military and other scientific research areas.Conventional imaging based optical imaging is essentially a process of acquiring a picture of a target through an imaging system and applying computer technology to extract target topographical information therein.Therefore,to obtain the target image,improve the image quality and improve the similarity between the acquired image and the target is the key to optical imaging measurement.Optical imaging can be divided into two categories: traditional imaging and light field(computing)imaging according to the acquisition method of the target image.For the traditional imaging system,the core components are lens and area array detectors.The structure is difficult to change after once designed,processed and assembled.The imaging process is a simple copy of the object's two-dimensional scene.The amount of information is not enough and a lot of effective information is lost.In contrast,the light field imaging system has no fixed structure,and the components can be adjusted with each other.The overall idea of the system design is no longer to obtain a two-dimensional image signal with high resolution,but only the only the information that the image understanding algorithm needs to collect,which achieved a leap from "two-dimensional to information".Different from traditional imaging technology,light field imaging technology,is an emerging optical imaging method,can effectively modulate the timing,phase,amplitude,wave front,dispersion,etc.of optical signals by adjusting the spatial and temporal parameters of the optical field.Object characteristics,thereby obtaining an optical image of a coded light field or high spatial and temporal resolution that cannot be obtained by a conventional imaging system.Using the acquired high-dimensional or coded light field information,various physical quantities such as depth,angle,and contour of the reconstructed object space can be calculated,which will certainly broaden the applicable scene of the optical imaging system and can be better applied to optical measurement.However,the existing optical measurements are mostly based on traditional imaging technology.With the continuous development of science and technology,in some physical quantity measurement,the existing optical measurement can no longer meet the requirements of human exploration of the unknown world.For example,traditional topography measurement techniques are more demanding on ambient light and require higher reflectivity.Today's scientific research often requires the detection of the shape of the target in extremely harsh environments such as the deep sea.In the extremely dark or high turbidity environment,traditional imaging technology will not be able to obtain the target information;in addition,the traditional optical system has limited field of view.The target information outside the field of view will be lost,greatly reducing the measurement range and accuracy.Besides,a single traditional imaging system cannot achieve the acquisition of three-dimensional information of the stereo target,and at least two systems need to cooperate with each other,with high complexity and calibration which is difficult.Aiming at the above problems and combining practical experience,this thesis systematically studies the compressive sensing single-pixel imaging technology,compressed sensing computational reconstruction,distance gating,digital refocusing,depth surface image and focus stack calculation reconstruction,depth map calculation,etc.Key purpose is to reconstruct the 2D and 3D target reconstruction solutions based on focused light field imaging technology,effectively solving various problems including but not limited to the traditional measurement techniques listed above.The main contents of the article are summarized as follows:(1)Firstly,aiming at the key problem of computational reconfiguration in singlepixel imaging,a high-speed and high-accuracy reconstruction method based on compressed sensing is proposed,which provides powerful theoretical support for the subsequent system application.For the transmissive and reflective two-dimensional target imaging,the corresponding active mode single-pixel imaging model is presented.Based on the imaging model,the corresponding active single-pixel detection system is built.The acquired discrete sample values are used to calculate the two-dimensional target.Refactoring.On the basis of the successful reconstruction of the target,the system and environmental factors affecting the quality of system reconstruction are analyzed in detail.In terms of system factors,the effects of single pixel detector effective pixel area,micro mirror array configuration,sampling times and observation pattern types on system reconstruction quality are discussed,and a targeted solution is proposed.For the analysis of environmental factors,the laser echo equation and the medium transmittance equation are introduced.The effects of medium turbidity and target distance on system performance are analyzed through simulation and experimental discussions.In the process of analyzing environmental factors,the imaging system can detect and detect targets in high turbidity environment.In order to further reflect the advantages of singlepixel light field imaging technology,a traditional imaging system is constructed,which is different for turbidity.The quality of target reconstruction in the water medium was compared.(2)Secondly,based on the successful experience of the previous active mode singlepixel imaging system,the theory and system construction of passive mode single-pixel imaging technology is developed around the two-dimensional target detection problem in non-line-of-sight environment.Considering particularly occlusion target,in order to suppress the influence of stray light on the whole system,a synchronous control system based on distance gating is designed,and the logic excitation relationship between the instruments is introduced in detail.Based on the above research,a single-pixel system suitable for occlusion target detection is built.The sparse signal collected by the system is used to detect and reconstruct the two-dimensional reflective target outside the line of sight.In the experiment,it is found that the laser pulse has a strong anisotropic reflection when it is reflected on the target surface,which affects the performance of the whole system.Therefore,based on the previous study of the laser echo equation,the laser with the target surface characteristics is obtained.The echo equation is validated by a large number of comparative experiments.In addition,an occlusion target detection system based on the imaging system is built and the detection results are compared and analyzed.(3)Finally,based on the detection of two types of two-dimensional targets in different environments,the key problem of depth image acquisition in target threedimensional information is studied in two parts,namely four-dimensional light field processing based on lens array and Target detection for single pixel imaging.Based on the single-shot acquisition of microlens array light field imaging,the properties of fourdimensional light field information in object space can be obtained.Combined with the focus stack model and slice projection theorem,a filtered back projection algorithm is proposed,which can be high in a short time.The quality obtains the focus stack through the four-dimensional light field information,and theoretically analyzes the perspective reconstruction of the four-dimensional light field information.Based on the theoretical analysis,a light field acquisition system based on microlens array is built.The proposed algorithm is verified by focusing stack reconstruction and perspective transformation on the acquired 4D light field image.In addition,combined with the principle of active single pixel and time flight,a new three-dimensional target single-pixel imaging detection method is proposed.The detection model is established and the experimental system is built to detect the three-dimensional target.In this paper,light field imaging is the main focus,and the key theory and practical application in light field imaging are comprehensively studied through four directions from two-dimensional to three-dimensional,from exposure to occlusion,from algorithm to experiment.The development has played a good role in promoting.