Research On Imaging Technology Based On Light Field Measurement

Traditional imaging only records the position information of light,but loses the light angle information which is highly coupled with the depth of the scene,the geometric shape of the target and so on,resulting in a series of irreconcilable problems in focus and the depth of field.Due to its special optical structure,the light field camera can simultaneously record the position information and direction information of light in a single exposure whose imaging mode is a digital imaging mode of “first photographing,then focusing”.With this camera,the focal plane can be specified manually and the depth of field of imaging system can be extendable,so many problems in traditional imaging can be solved.When the above optical imaging systems are affected by aberrations such as atmospheric turbulence,the imaging quality of the optical system will be greatly reduced.Traditional methods for overcoming aberrations such as atmospheric turbulence mainly include adaptive optics and image post-processing.Adaptive optics requires a guide star for wavefront measurement.The structure of this system is complicated and costly,thus it is difficult to apply this technology on a large scale for some miniaturized devices.As for image post-processing,this method has special requirements on the image shooting conditions,the number of samples and the prior information of the image.The data is also computationally intensive.It is difficult to achieve real-time or quasi-real-time with this system,and it is not applicable for clear imaging of high-speed moving targets.Aiming at the problems of traditional imaging in focusing and depth of field,the problems of low imaging quality when optical imaging system is affected by aberrations,and the limitations of traditional methods for overcoming aberrations,this paper carries out in-depth theoretical and applied research focusing on technologies including light field imaging,light field digital refocusing and light field wavefront measurement.And a series of innovations have been made,the main work of this paper are as follows:1.The theory of light field imaging and the theory of light field wavefront measurement are deeply studied.The error and the accuracy of light field wavefront measurement are analyzed.The method of light field modulation is proposed to improve the accuracy of light field wavefront measurement.According to the theoretical model of the light field measurement,the numerical simulation platform of light field imaging and light field wavefront measurement is established on MATLAB numerical simulation software by using the ray tracing method.We have implemented light field imaging,digital refocusing,wavefront measurement,and wavefront restoration for a 2D extended targets.The simulation results show the light field camera can effectively measure and reconstruct the target's distortion wavefront,and show the influence of the f-number matching between the main lens and the microlens array of the light field camera,and verify the removal effect of the refocusing algorithm on the defocus aberration.2.A new high-resolution imaging system combining a light field camera and a traditional camera is designed.The system uses a beam splitter to position the image surface of the traditional camera and the microlens array surface of the light field camera on the conjugate plane.The wavefront information of the target is obtained by the light field camera and it is used to solve the point spread function of the system,and then deconvolution with the blurred image captured by the traditional camera to obtain the reconstructed high-resolution image.This device can solve the problem that the imaging quality of the optical system is not high under the influence of aberrations such as atmospheric turbulence.In addition,the system complements the advantages and disadvantages of the light field camera and the traditional camera.It solves the problems of the traditional camera in focusing and depth of field through the light field imaging,and compensates for the low spatial resolution of the light field camera through the conventional imaging.Numerical simulation results verify the effectiveness of the proposed method.3.A high-resolution imaging technique based on light field manipulation is proposed.This method calculates and compensates the offset of each sub-aperture image due to the influence of aberrations by image correlation algorithm,thereby shaping the target's wavefront to solve the problem of poor imaging quality of light field camera under the influence of aberrations and to reduce the influence of partial aberrations on the light field camera imaging system.The error of the method is analyzed.The laboratory light field camera is designed,calibrated and decoded.The simulation and experimental results verify the effectiveness of the method.The main advantages of this method are as follows.Firstly,only the raw light field data captured by the light field camera in a single exposure is used,thus no additional hardware equipment is needed,and the cost is low.Secondly,the wavefront measurement does not require a guide star,the light energy utilization rate of the system is higher and the system structure is simpler.Lastly,the parallax information of the light field subaperture images are preserved.4.A high-resolution imaging technique based on light field screening is proposed.This method uses image correlation algorithm to screen out some sub-aperture images with better quality when subjected to aberrations for digital refocusing,which can solve the problem of poor imaging quality of light field camera under the influence of aberrations and reduce the influence of partial aberrations on the light field camera imaging system.Simulation and experimental results verify the effectiveness of the proposed method.The main advantage of this method is that only the raw light field data captured by the light field camera in a single exposure is used,no additional hardware equipment is needed,the cost is low and the method is easy to apply.5.A high-resolution imaging technique combining light field screening method and light field manipulation method is proposed,which firstly compensates the offset generated by each sub-aperture image due to the influence of aberrations,and then selects some high-quality sub-aperture images for digital refocusing to obtaining a highresolution image.It further improves the imaging quality of the light field camera imaging system under the influence of aberrations.Simulation results verify the effectiveness of the proposed method.The techniques proposed in this paper can be used to analyze lens distortion,water turbulence in underwater imaging,and image distortion caused by atmospheric turbulence in remote sensing imaging.These techniques are of great application value in the fields of astronomical target detection,remote sensing imaging,etc.