| More than 70%of the total external information can be obtained with the visual system of humans,so providing accurate and effective visual content is the fundamental driving force for the development of display technology.The complete depth information of the external environment in the objective world can be perceived by the human visual system with three-dimensional(3D)form,so that the spatial orientation of arbitrary object can be obtained to help humans fully understand and reasonably judge surrounding things.The flat display technology can only provide two-dimensional(2D)flat information,and cannot stimulate the human visual system to perceive depth information,which is inconsistent with the way of perceiving the objective world for the human visual system.The autostereoscopic display is an important development direction of 3D display technology,which can present 3D display content with different view information and depth information for the observer without wearing visual aids.Therefore,in recent years,the autostereoscopic display has attracted widespread attention in academics and industrial circles worldwide.However,the traditional autostereoscopic display suffers from a bottleneck problem of the low resolution,and it restricts the further development and application of this display technique.Low resolution of the autostereoscopic display includes two aspects including insufficient viewpoint angular resolution and low spatial resolution.Viewpoint angular resolution is the number of viewpoints per angle,and it characterizes the continuity of 3D information.Unsmooth motion parallax and convergence-accommodation conflict(CAC)of the 3D image can be caused due to insufficient viewpoint angular resolution.CAC will cause observers to feel dizzy and sharply deteriorate 3D display quality.Spatial resolution is the number of secondary light sources fornled by the convergence of viewpoint light rays and it characterizes the fineness of 3D images.The lack of spatial resolution will reduce the accuracy and effectiveness of 3D data visualization.Aiming at the problem of low resolution of the traditional autostereoscopic display,methods of improving viewpoint angular resolution and spatial resolution are proposed in this paper.The main innovation points and research content of this dissertation are as follows:(1)Light field display with high viewpoint angular resolution based on pixel horizontal modulationKey point 1:The full-parallax 3D image of the original scene can be recovered with integral imaging.The displayed 3D image has various advantages,such as smooth motion parallax and outstanding three-dimensional impression.Based on the principle of the construction of full-parallax light field of integral imaging,the method of the construction of horizontal light field is proposed in this paper.In the case of limited flat resolution of the 2D display device,light rays emitting from pixels of the flat display device is horizontally modulated with specific horizontall direction angles to integrate viewpoints in the horizontal direction,which is achieved by the use of the micro-pinhole unit array or the discrete lenticular lens array.As a result,a significant increase in the viewpoint angular resolution can be achieved.This method can realize high-quality 3D image with dense multi-viewpoints in a wide viewing angle.The micro-pinhole unit array is based on the principle of pinhole imaging to modulate the light rays,which emit from pixels per line of the elemental image array,with specific horizontal direction angles to integrate the light field with horizontal parallax.The micro pinhole unit array has the advantages of high light-controlled accuracy,no aberrations,large size and low cost.In the consideration of the same pixel horizontal modulation capability,compared to using the micro pinhole unit array,the optical efficiency has been significantly improved with the discrete lenticular lens array.In the diplay prototype,high quality 3D images with the angular resolution of 2.3 viewpoints/degree can be provide in the viewing angle of 42.8°.(2)High-resolution light field display with suppressed-crosstalkKey point 2:A small-pitch micro-pinhole unit array is used to form the horizontal light field with ultra-high viewpoint angular resolution,which can realize that multiple viewpoints can be perceived by a single eye.As a result,monocular adjustment can be stimulated and CAC can be eliminated.However,it suffers from high crosstalk between viewpoints when using a small-pitch micro-pinhole unit array to achieve pixel horizontal modulation.The smaller the pixel size,the more serious the crosstalk.The larger the vie.Arpoint angular resolution and the denser the viewpoint distribution,the more serious the deterioration of 3D display quality caused by the crosstalk.The viewpoint crosstalk is caused owning to the stray light crosstalk of adjacent rows of pixels in the elemental image array.In order to solve this problem,the vertically-collimated backlight is designed and used,instead of the scattered backlight,to effectively suppress the stray light crosstalk in the 3D display system.Thus,high viewpoint angular resolution light field display with low crosstalk is realized.Besides,the spatial resolution of the displayed 3D image is also improved because one eye can observe multiple viewpoints.In the demonstrated diplay prototype,high quality 3D images with less than 7%crosstalk can be displayed with the angular resolution of 39.2 viewpoints/degree,the spatial resolution of 1280×1080 and the monocular resolution of 1920×1080.Key point 3:In order to increase the viewing angle of the proposed 3D display with high viewpoint angular resolution and spatial resolution,a real-time retina-based light field reconstruction method is proposed in this paper.According to the real-time 3D position of the human eye,the light field information within the cone angle of human eye is captured and recovered in real time to achieve 3D image with large viewing angle and high viewpoint angular resolution and spatial resolution.The real-time retina-based light field reconstruction method realizes the real-time correct mapping between the pixels of the parallax images and the pixels of the elemental image array loaded on the flat display device at the current time,which ensures that the 3D image has the correct occlusion relationship and spatial stereoscopic perspective.A large viewing angle of 50°is realized with the display prototype.(3)High-resolution integral imaging based on space-time multiplexing lens stitchingKey point 4:Integral imaging can recover the full-parallax light field of the original object,and natural 3D image can be observed.However,its low spatial resolution restricts the clarity of 3D data visualization and reduces the accuracy and effectiveness of information transmission.In addition,narrow viewing angle is another inherent drawback of integral imaging.The application and development of integral imaging is greatly limited due to these two drawbacks.The method of the space-time multiplexing lens stitching is proposed in this paper,which can significantly improve both the viewing angle of integral imaging and can also increase the spatial resolution by several times.The directional time-sequential backlight is designed and used to realize space-time multiplexing lens stitching.Collimated backlight beams with specific directional angles can be provide with the directional time-sequential backlight in time sequence.By predesigning the optical parameters of the directional time-sequential backlight and the lens array,the collimated backlight beams with different direction angles are converged through adjacent lenses of the lens array,so that the equivalent pitch of the lens array is several times as large as the inherent pitch.As a consequence,the viewing angle is enlarged.Besides,the collimated backlight beams have different direction angles at different times to form dense point light sources with different spatial positions.When the refresh rate of the backlight is sufficiently high,the number of point light sources is several times that of lenses in the array due to the visual persistence effect of the human eye.As a result,the spatial resolution of the 3D image of the proposed integral imaging is several times that of the traditional integral imaging.In the demonstrated diplay prototype,floating full-parallax 3D light-field images can be perceived with 4 times the viewing resolution enhancement in the viewing angle of 50°,where 7056 viewpoints are presented. |
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