Target Reconstruction Through Scattering Media Based On Point Scattering Model In Phase Space

Scattering media widely exists in nature,such as biological tissue,cloud,smog,turbid water and so on.The presence of scattering media seriously affects the quality of optical imaging,which brings great challenges to applications that are highly dependent on imaging,e.g.,medical diagnosis,auto navigation,fire rescue and deep-sea exploration.In recent years,more and more attentions have been paid to imaging through scattering media.How to overcome the scattering effect to achieve clear imaging has become a research hotspot in the field of computational imaging.At present,there are many research methods about imaging through scattering media,each of which has advantages and disadvantages.In this paper,the imaging target is regarded as the sparse distribution of point light source,and how the light field of point light source changes after passing through the scattering medium is analyzed.The optimal estimation of the target image is achieved by minimizing the difference between the scattered light field of the target predicted by the model and the actually measured light field.Light field is the propagation and distribution of light intensity in space,which needs to be described in a high-dimensional(usually four-dimensional)space.This high-dimensional space is conventionally called phase space.Based on the above two models of light field,the thesis has completed the following research works:1.Reconstruction of targets through scattering media based on the Wigner function of light field.Firstly,starting from the Wigner function of the light field,the light field of the point light source after being scattered by the medium is deduced via the forward propagation of light.From the perspective of discrete sampling,the imaging target is regarded as a set of multiple point light sources in three-dimensional space.The light field distribution of the target after scattering is the superposition of the scattered phase space functions corresponding to each point light source,and the prediction of the scattered light field is obtained.Then,a 4f spatial filter system is built to collect data of light field.By changing the position of the clear aperture on the spectrum plane of the 4f system,the angular frequency of the light field is sampled.An area array camera is used to record the two-dimensional spatial distribution of the light field at different angular frequencies,which provides the measured data of light field after the target is scattered.Finally,the difference between the predicted light field and the measured light field is minimized by constructing a linear regression problem,and the sparse distribution of the corresponding point light sources is the reconstructed target.2.The control of the clear aperture in the experimental system is realized by digital micromirror device(DMD).Due to the periodicity of the pixel distribution in the DMD,there is significant diffraction on the optical path.By analyzing the diffraction characteristics of the DMD,an appropriate incident angle is selected so that the maximum diffraction direction coincides with the blaze direction,which ensures that the system has a high efficiency for light transmission.3.Reconstruction of targets through scattering media based on the bi-plane model of light field.Firstly,in the case of imaging on certain viewpoint,the spatial distribution of the point light source after being scattered by the medium is analyzed.And the sampling of the ray direction is introduced by moving the viewpoint.Thereby the prediction model of the scattered light field is constructed under the framework of geometric optical imaging.Then,the actual light field of the target after scattering is recorded by a camera with multiple translations.Finally,an optimization problem similar to the previous work is established to solve the 3D reconstruction of the target.The feasibility of the method is proved by the simulation and experiments for multiple discrete point targets and continuous light-emitting target.Theoretically,there is no requirement for the wavelength and coherence of illumination.And only a movable camera is needed on the system rather than complex optical path.The advantages of this method lay a good foundation for the future work on target reconstruction of outdoor scenes.