Research On Digital Refocusing Based On Optical Field Imaging

In the process of traditional camera shooting,the camera parameters need to be set in advance,and only the intensity information of one image plane can be obtained,which greatly limits the richness of image information.The light field camera can shoot first and then image through digital refocus in the later stage.The advantages of flexible depth of field control and easy depth of field expansion make the light field camera have strong applicability in the process of detecting the multi-dimensional characteristics of the target,so it has broad application prospects and research value.Firstly,this paper analyzes the description of light field,the principle and technology of light field imaging,and compares the advantages and disadvantages of pinhole array and microlens array sampling;The light field sampling based on microlens array realizes the surface sampling method.The collected light field information is rich and there is no luminous flux loss,so this sampling method has more advantages.Starting from the phenomenon of defocus,the principle and implementation of digital focusing and digital zoom are deduced and analyzed,and the idea and principle of digital refocus are given;By analyzing the image translation and superposition in the focusing process of binocular stereo camera,the digital refocusing method of microlens array light field camera,that is,the superposition principle of sub aperture image,is discussed,and the algorithm of digital refocusing of light field image is analyzed from the spatial domain;According to the Fourier slice theorem,the algorithm of digital refocusing of light field image is analyzed in frequency domain.On the basis of theoretical research,the original light field image is taken by Illum light field camera,the original light field image is extracted by MATLAB,the algorithm program is written,and the experimental research of digital refocusing is completed.The results show that for the selected refocusing plane,the image definition of the scene on the plane is significantly improved after refocusing,and the farther away from the plane,the more blurred the image definition is.The reason is that the refocusing plane is obtained by the translation and superposition of all sub aperture images.The sub aperture images reflect the results of observation from different angles.Therefore,the farther away from the refocusing plane,the greater the image displacement caused by different observation angles and the more blurred after superposition.According to the principle and method of digital refocusing,two methods of measuring light field depth information are designed,namely reference plane method and calibration method.The reference plane method is to know the depth of a certain scene plane,and determine the focusing depth coefficient between it and the plane to be measured by digital refocusing to measure the depth information;When the camera parameters are fixed,the calibration method first moves the scene surface in turn to take the light field image,and uses the digital refocus to complete the calibration of the focusing depth coefficient,then digitally refocus the light field image to be measured taken by the parameter camera to obtain the focusing depth coefficient of the surface to be measured,and finally measure the depth information by comparing with the calibration results.Then the experimental scene is designed,and the application and measurement error of the two measurement methods are studied.The results show that when the position far from the lens is selected as the reference plane,the maximum relative error of the experimental measurement is less than 8%,and the farther the reference plane is from the camera lens,the smaller the relative error is;When the reference surface is selected,the farther the distance from the surface to be measured to the camera lens,the smaller the relative error of measurement,and the more accurate the result of depth measurement.For the calibration method to measure the scene depth,the relative error is less than 5% within the calibration range;If the surface to be measured is a single plane scene,the measurement relative error is randomly distributed;If the light field composed of multiple scene planes is to be measured,the relative error of measurement increases with the increase of the distance from the scene plane to the camera lens.Comparing the two measurement methods,the calibration method is obviously better than the reference plane method.First,the relative error of measurement is small.Second,when the calibration method is used,it only needs to complete one calibration with the known light field scenery,which can be used for many times,and does not need any information of the light field to be measured.In the process of studying the measurement of light field depth information,aiming at the effect of digital refocused image,this paper introduces image sharpness evaluation,discusses and compares the characteristics of three image sharpness evaluation functions,and gives that Brenner function should be preferred as the sharpness evaluation function of refocused image.