Title Page
Abstract
국문요약
Contents
Chapter 1. Introduction 22
1.1. 3D camera 22
1.2. What is Light Field Camera? 25
1.3. Objective and Outline 28
Chapter 2. Microlens array with low sag height for light field camera 32
2.1. Introduction 32
2.2. Geometrically controllable MLA fabrication method 36
2.3. light field camera demonstration 40
2.4. Summary 48
Chapter 3. Vari-Focal Light Field Camera for Extended Depth of Field 50
3.1. Introduction 51
3.2. Optimize MLA focal length for variable-focal lens 53
3.3. Implementation and experimental measurement of vari-focal light field camera 60
3.4. Summary 67
Chapter 4. A Wide Field-of-View Light-Field Camera with Adjustable Multiplicity for Practical Applications 68
4.1. Introduction 69
4.2. Multiplicity optimization for wide-FOV LFC 71
4.3. Implementation and characteristics of LFC with Wide-FoV 80
4.4. Summary 89
Chapter 5. Miniaturized 3D Depth Sensing-Based Smartphone Light Field Camera 91
5.1. Introduction 92
5.2. Ray-tracing simulation for one-aperture structure with optimal MLA thickness 94
5.3. Implementation and characterization of miniaturized LFCs in smartphone 102
5.4. Summary 108
Summary 110
References 112
HYUN MYUNG KIM'S CURRICULUM VITAE 130
Table 2.1. Normalized sharpness of the refocused processed image 45
Table 2.2. Detailed camera measurement parameters 48
Table 3.1. Parameters of MLA and image sensor 61
Table 3.2. Intrinsic parameters for vari-focal light field camera. 62
Table 3.3. Light field camera classification. 64
Figure 1.1. (a) Schematic of a conventional camera capturing an object on an image sensor. (b) Schematic of a three-dimensional camera capturing an object on an image... 23
Figure 1.2. The development of 3D media has led to a surge in demand for three-dimensional cameras in various applications. 23
Figure 1.3. The schematic on the operating principles of a three-dimensional camera, respectively (a) stereoscopic vision, (b) structure light, (c) time-of-flight. 24
Figure 1.4. The schematic of the difference between a conventional camera and a light field camera for the same object measurement. (a) Conventional cameras capture only... 26
Figure 1.5. Different MLA-based light field camera geometrical optic models. (a) Conventional light field camera, (b) Keplerian configuration of light field camera 2.0, (c)... 27
Figure 2.1. Description of a light field camera based on microlens array (MLA). 35
Figure 2.2. (a)Difference in the focusing ability of MLA based on the radius of curvature (RoC). (b) Plot of an active fill factor with different F-numbers of the main lens. The... 35
Figure 2.3. Schematic illustration of the overall MLA fabrication procedure. 37
Figure 2.4. Schematic of formation of a hemispherical shape of quartz mold via the HF solution depicted in (iv) of Figure 2.3 38
Figure 2.5. (a)Schematic illustrations of non-uniform quartz etching. (b) Scanning electron microscope (SEM) image of the non-uniformly formed quartz mold. Red points... 39
Figure 2.6. Schematic illustration of the wet etching procedure for the uniform mold with low sag height and high RoC. 39
Figure 2.7. SEM images of quartz molds with two different lattice patterns 40
Figure 2.8. SEM images of quartz molds with different etching times. 40
Figure 2.9. Graph of RoC versus HF etching time with respect to two different Poly-Si removal times. 41
Figure 2.10. (a) Optical image of bare PDMS (left) and fabricated PDMS MLA (right). (b) SEM image of PDMS MLA with a high RoC of 139 μm and low sag height of 3 μm. 41
Figure 2.11. Schematic illustration of integration with a fabricated PDMS MLA and digital camera. 42
Figure 2.12. (a)Photograph of the measurement setup to validate the applicability of the light field camera. (b)Raw data was obtained via the hand-crafted light-filed camera. 43
Figure 2.13. Processed sub-aperture image showing the multi-viewpoint property of the light field camera. 43
Figure 2.14. Principle of the multi-viewpoint property in the light field camera. 43
Figure 2.15. View point difference between viewpoint 1 and viewpoint 2. 44
Figure 2.16. Results of light field image processing. (a)Image of light field refocusing processing. (b) Normalized sharpness graph of the refocused image at 30, 60, and 90cm. 45
Figure 2.17. All-in-focused image by using the focal stacking method. 46
Figure 2.18. Test of the light field camera for practical use. Two indoor tests include billiard and tape measure objects for general and zoomed-in objects. Outdoor test for... 47
Figure 3.1. (a) Schematic of conventional light field camera. (b) The disparity of the conventional light field camera decreases and converges. 54
Figure 3.2. (a) proposed light field camera with a vari-focal lens. (b) By controlling the focal length before the disparity converges, the proposed VF-LFC provides an... 55
Figure 3.3. Schematic of the VF-LFC system with main design parameters. 58
Figure 3.4. Schematic of the optical path through the MLA between the image sensor and the image plane of the main lens. 58
Figure 3.5. The image side DoF, a₊ and a₋, are calculated from the thin lens equation for a focal length of MLA. 59
Figure 3.6. The object side DoF for each focal length of a vari-focal lens according to the MLA focal length, the dotted lines are the boundaries between measurement... 59
Figure 3.7. (a) Schematic of optical alignment module for VF-LFC. (b) Photographs of the assembled module for VF-LFC. 60
Figure 3.8. Photographs of light field image captured by VF-LFC with focal length FL 20 mm (left), and FL 75 mm (right), inset: original texture image. 61
Figure 3.9. Photograph of the VF-LFC and reference image (inset). 63
Figure 3.10. Schematic of VF-LFC experimental setup according to the measurement regions for each focal length. 63
Figure 3.11. Micro-images from VF-LFC at four different focal lengths. 63
Figure 3.12. Graph of the disparity according to object distance, solid lines are calibrated result and red dots represent the experimental result. 64
Figure 3.13. (a) Photograph of sequential depth measurement setup with the VF-LFC. (b) Micro-images from VF-LFC at four different focal lengths. (c) Stitched image with... 65
Figure 3.14. (a) Photograph of outdoor measurement setup of VF-LFC. (b) Microimages from VF-LFC at four different focal lengths. (c) Photographs indicate the field of... 66
Figure 4.1. Schematic of the proposed light-field camera (LFC) for wide field-of-view (FOV) with several objects. The overlapped area is optimized with adjustable multi-... 73
Figure 4.2. Linear plot of pixel per degree (PPD) versus M for wide (60°) and narrow... 74
Figure 4.3. Schematic images of individual lenses with maximum ratios of PPD and overlapping ratio (OR) according to several M (1, 2, and 4) in each wide (60°) and... 74
Figure 4.4. Schematic of wide FOV-LFC optical structure with several design parameters in Keplerian mode. 75
Figure 4.5. Schematic of ray propagation path between the image sensor and image plane with different M. 75
Figure 4.6. Calculated disparity error according to as a function of baseline from microlens projection image. 78
Figure 4.7. Calculated depth accuracy considering PPD and baseline as M variation at each narrow (20°) and wide (60°) FOV, respectively. 79
Figure 4.8. Sharpness from captured images according to different M (2, 3, and 4). 79
Figure 4.9. Schematic of optical alignment module for wide FOV-LFC. (b) Photographs of the spacer adjustable optical alignment module for wide FOV-LFC. 81
Figure 4.10. Micro-lens images captured by wide FOV-LFC with multiplicity M = 2 (left), and M = 4 (right). 81
Figure 4.11. (a) Schematic of point spread function (PSF) measurement with axis moving stage. (b) Photograph of an experimental setup with a laser beam diameter of... 82
Figure 4.12. Captured PSF images (top) and illuminance intensity distribution of PSF (bottom), peak intensities (right) according to axis moving with 0-3 mm at (a) M =... 84
Figure 4.13. (a) Photograph of object-measurement set up of wide FOV-LFC. (b) Law data image captured from wide FOV-LFC. 85
Figure 4.14. Pre-processed images from captured object image. at (a) M = 2 and (b) M = 4. 86
Figure 4.15. Disparity maps extracted from captured object images at (a) M = 2 and (b) M = 4. 86
Figure 4.16. Calibration result of disparity plots with different distances at M = 2 is shown by the blue line, and M = 4 is the apricot line. 88
Figure 4.17. Disparity plots with different distances extracted from captured object images at (a) M = 2 and (b) M = 4 88
Figure 4.18. Depth step plot by distance section of the object. M = 2 is blue bar, and M = 4 is apricot bar. 88
Figure 5.1. Schematic of a conventional light field camera (LFC). 94
Figure 5.2. Schematic of a minimized LFC structure with only one aperture. 95
Figure 5.3. (a) Photograph of a minimized LFC integrated into a smartphone. (b) Magnified photograph of a micro-lens array (MLA) stacked on an image sensor. The... 95
Figure 5.4. Demonstration of the multi-viewpoint image acquisition of the proposed module. 96
Figure 5.5. Schematic of the analysis parameters for the miniaturized LFC system. 96
Figure 5.6. Schematic of the ray-tracing simulation for micro-lens without space and without space with the same radius, and comparison of root-mean-square (RMS) spot radii. 97
Figure 5.7. Optimum MLA thickness according to the micro-lens radius. 98
Figure 5.8. Image acquisition simulation results according to the aperture distance from the MLA. 98
Figure 5.9. Multi-viewpoint image acquired using the minimized LFC smartphone camera. 99
Figure 5.10. Procedure schemes for quartz MLA mold fabrication. 100
Figure 5.11. Schematic of the replica molding process of the poly-dimethylsiloxane (PDMS) MLA. The inset shows an SEM image of the fabricated quartz master mold... 101
Figure 5.12. The graph shows that the MLA thickness is linearly proportional to the poured PDMS weight in a Petri dish with a diameter of 100 mm. 101
Figure 5.13. A magnified schematic of the configuration of the minimized LFC system. 102
Figure 5.14. (a) Photograph of the checkboard image for calibration with the miniaturized LFC system. (b) Reference point image on the checkboard to perform camera calibration. 103
Figure 5.15. (a) Photograph of the Lena picture captured by the miniaturized LFC. (b) Images of wider view angles were obtained using image stitching techniques from... 103
Figure 5.16. Schematic of ray tracing for the calculation of the pixel shift. Parameters Sref., Scont., and d represent the reference point source, control point source, and dis-...[이미지참조] 105
Figure 5.17. Contour image of the simulation results according to the distance of the point source. Each image shows 7 view-point differences. The red spot depicts the... 105
Figure 5.18. Graph of the pixel shift according to the point source location. 106
Figure 5.19. (a) Photograph of measurement condition. (b) The image is captured with the mobile light field camera. 107
Figure 5.20. Post-processed image with the obtained light field image. Each layer represents the original image (bottom layer), disparity map (middle layer), and reconstructed... 108