Research On Light Field Imaging Application In Sky Light Polarization Detection And Resolution Enhancing For Image Distorted By Turbulence

Because light field imaging technology can capture plenty of information of the target,it has many new functions that many traditional ways of imaging don't have.Light field imaging is undergoing a fast development recently.In parallel,how to comprehend,express and use the concept of light field better becomes a new research focus.This paper tries to explore the new applications of light field imaging in sky light polarization detection and resolution enhancing for images disturbed by turbulence.First of all,we introduce a new optical structure to measure the sky light polarization pattern across a wide field of view in real time.This structure employs a hand held light field camera,a wide field lens and to simulate the insect compound eyes' capability of polarization information sensing and navigation.Two different computation methods' influence to detection accuracy are analyzed theoretically and it is found that the computation result based on a linear polarizer triplet is better than four-quadrant polarizer.The experimental results match well with the predicted theoretical sky light polarization pattern.In order to extract the orientation of the sun,the angle of polarization data is redrawn in new reference coordinate system to make the symmetry with respect to the line of sun meridian visualized easily.The orientation of the sun then can be extracted from the symmetry axis of angle of polarization image and the direction angle can be calculated.More group of experiments are carried out to test the performance of our system under different weather condition.The experimental results show that the direction angle accuracy in clear sky is higher and the overcast sky and the haze may decrease the precise of the polarization detection results seriously.In addition,the experimental results are also influenced by the thin cloud and strong sunlight and the degree of the influence is depend on the clouds' altitude and thickness.In summary,the images which were obtained through the method in this paper have an obvious symmetrical characteristic.It is easy to extract the heading information under different weather condition.Even when it is cloudy or haze pollution weather,when the degree of polarization is very low,the orientation of the sun can also be detected.An experimental system based on a handheld light field camera and a triplet linear polarizer is built.After calibrating the camera's response curve and correcting the vignetting effect,excellent sky light polarization measurement results are obtained.In order to explore new method to further enhance the robustness of the system affected easily by the cloud and sunlight,the triplet linear polarizer is replaced by a radial polarizer.This modification decreases its dependence on Stokes function and makes it rely on the captured image itself to get the sky light polarization pattern.The performance of the system under cloudy sky can be improved.So it might be a method with good potential for growth and application.About the research work on resolution enhancing for images disturbed by turbulence,a lucky region imaging method based on the comparison of two symmetrical defocused light field is proposed.A numerical simulation for the defocused image of a point object is conducted and shows that the image sharpness can be evaluated accurately through the analyzing the difference between two defocused images.After applying this evaluation criterion to extended target,the concept of lucky region imaging is proposed.The experimental results show that difference between two defocused images can reflect the image's degradation degree with high sensitivity,which verified the feasibility of lucky region imaging method based on the comparison of two symmetrical defocused light field.