Search query: Light field imaging

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abstract: The core of any optical imaging system is a photodetector. Whether it is film or a semiconductor chip in a camera, or indeed the retina in an eye, conventional photodetectors are designed to absorb most of the incident light and record a projected two dimensional (2D) distribution of light from a scene. The intensity distribution of light from 3D objects, however, can be described by a 4D light field, so optical imaging systems that can acquire higher dimensions of optical information are highly desirable 1 3 Here, we report a proof of concept light field imaging scheme using transparent graphene photodetector stacks. On a transparent substrate we fabricate a photodetector using graphene as the light sensing layer, the conducting channel layer, the gate layer and interconnects, enabling sensitive light detection and high transparency at the same time. This technology opens up the possibility of developing sensor arrays that can be stacked along the light path, enabling entirely new configurations of optical imaging devices. We experimentally demonstrate depth ranging using a double stack of transparent detectors and develop a method for computational reconstruction of a 4D light field from a single exposure that can be applied following the successful fabrication of dense 2D transparent sensor arrays. A highly transparent photodetector using graphene as the light sensing layer, conducting channel layer, gate layer and interconnects enables new approaches for light field photodetection and imaging involving simultaneous detection across multiple focal planes.
author_names: Miao-Bin Lien

Che-Hung Liu

Il Yong Chun

Saiprasad Ravishankar

Hung Nien

Minmin Zhou

Jeffrey A Fessler

Zhaohui Zhong

Theodore B Norris
title: Ranging and light field imaging with transparent photodetectors
year: 2020

abstract: A light field camera captures both the intensity and the direction of incoming light1 5. This enables a user to refocus pictures and afterwards reconstruct information on the depth of field. Research on light field imaging can be divided into two components: acquisition and rendering. Microlens arrays have been used for acquisition, but obtaining broadband achromatic images with no spherical aberration remains challenging. Here, we describe a metalens array made of gallium nitride (GaN) nanoantennas6 that can be used to capture light field information and demonstrate a full colour light field camera devoid of chromatic aberration. The metalens array contains an array of 60 x 60 metalenses with diameters of 21.65 mm. The camera has a diffraction limited resolution of 1.95 mm under white light illumination. The depth of every object in the scene can be reconstructed slice by slice from a series of rendered images with different depths of focus. Full colour, achromatic light field cameras could find applications in a variety of fields such as robotic vision, self driving vehicles and virtual and augmented reality.A metalens array of GaN nanoantennas is used to make a full colour achromatic light field camera.
author_names: Vin-Cent Su

Shuming Wang

Mu Ku Chen

Jia-Wern Chen

Ji Chen

Yi-Teng Huang

Jung-Hsi Wang

Zhenlin Wang

Din Ping Tsai
title: Achromatic metalens array for full colour light field imaging
venue: Nature Nanotechnology
year: 2019

abstract: Light field microscopy through bare optical fiber bundles paves the way for depth resolved fluorescence microendoscopy. Optical fiber bundle microendoscopes are widely used for visualizing hard to reach areas of the human body. These ultrathin devices often forgo tunable focusing optics because of size constraints and are therefore limited to two dimensional (2D) imaging modalities. Ideally, microendoscopes would record 3D information for accurate clinical and biological interpretation, without bulky optomechanical parts. Here, we demonstrate that the optical fiber bundles commonly used in microendoscopy are inherently sensitive to depth information. We use the mode structure within fiber bundle cores to extract the spatio angular description of captured light rays the light field enabling digital refocusing, stereo visualization, and surface and depth mapping of microscopic scenes at the distal fiber tip. Our work opens a route for minimally invasive clinical microendoscopy using standard bare fiber bundle probes. Unlike coherent 3D multimode fiber imaging techniques, our incoherent approach is single shot and resilient to fiber bending, making it attractive for clinical adoption.
author_names: A Orth

Martin Ploschner

Emma R Wilson

I S Maksymov

Brant C Gibson
title: Optical fiber bundles: Ultra slim light field imaging probes
venue: Science Advances
year: 2019

abstract: Recently, intensive research on microlens array (MLA) was undertaken, which involved intertwining with the light field imaging in order to obtain four dimensional information. Although several fabrication approaches for MLA attempted to achieve high density and precision geometry, further progress is necessary. In this study, we present a cost effective fabrication strategy for geometrically tunable polymer MLA with extremely low sag height ~3 mm) through improved MEMS wet etching process. Additionally, we assemble a hand crafted light field camera by integrating the elaborately customized MLA with a commercial digital camera. Finally, we demonstrate representative light field imaging features including refocusing and all in focusing image from a single exposure.
author_names: Hyun Myung Kim

Min Seok Kim

Gil Ju Lee

Young Jin Yoo

Young Min Song
title: Large area fabrication of engineered microlens array with low sag height for light field imaging.
venue: Optics express
year: 2019

abstract: Abstract Light field imaging, which is one of the noncontact flame measurement methods, can capture and record multiangle radiative intensity information of a flame through a single shot. After the postprocessing and integration of the flame information, the three dimensional reconstruction of the temperature and radiative properties can be achieved. However, the diversity and universality of the reconstruction parameters make the reconstruction process complex and redundant. Therefore, the order of priority in which the radiative properties (attenuation coefficient, scattering albedo, and scattering phase function) of a flame influence light field imaging should be analyzed by simulation. This study aims to simplify the reconstruction process by simulating the light field imaging of nonuniform temperature distribution using a previously developed multifocus plenoptic camera model. In addition, a quality evaluation system is established to quantitatively analyze the optical influence of different radiative properties in the flame medium on the light field imaging process. The following conclusions are drawn by analyzing the aperture image of the flame with different radiative properties: (1) The attenuation coefficient should be the first priority for the reconstruction of the radiative characteristic parameters of the flame. (2) The scattering albedo should be the next consideration for ensuring high reconstruction precision. (3) For the scattering phase function, the only consideration is whether it is more affected by either isotropy or anisotropy.
author_names: Tianchan Li

Su-ning Li

Yuan Yuan

Fuqiang Wang

Heping Tan
title: Light field imaging analysis of flame radiative properties based on Monte Carlo method
year: 2018

abstract: Limited angular resolution has become the main bottleneck of microlens based plenoptic cameras towards practical vision applications. Existing view synthesis methods mainly break the task into two steps, i.e. depth estimating and view warping, which are usually inefficient and produce artifacts over depth ambiguities. In this paper, an end to end deep learning framework is proposed to solve these problems by exploring Pseudo 4DCNN. Specifically, 2D strided convolutions operated on stacked EPIs and detail restoration 3D CNNs connected with angular conversion are assembled to build the Pseudo 4DCNN. The key advantage is to efficiently synthesize dense 4D light fields from a sparse set of input views. The learning framework is well formulated as an entirely trainable problem, and all the weights can be recursively updated with standard backpropagation. The proposed framework is compared with state of the art approaches on both genuine and synthetic light field databases, which achieves significant improvements of both image quality +2 dB higher) and computational efficiency (over 10X faster) Furthermore, the proposed framework shows good performances in real world applications such as biometrics and depth estimation.
author_names: Yunlong Wang

Fei Liu

Zilei Wang

Guangqi Hou

Zhenan Sun

Tieniu Tan
title: End to End View Synthesis for Light Field Imaging with Pseudo 4DCNN
venue: ECCV
year: 2018

abstract: Light field imaging is a crucial and straightforward way of measuring and analyzing surrounding light worlds. In this paper, a dual polarized light field imaging micro system based on a twisted nematic liquid crystal microlens array (TN LCMLA) for direct three dimensional (3D) observation is fabricated and demonstrated. The prototyped camera has been constructed by integrating a TN LCMLA with a common CMOS sensor array. By switching the working state of the TN LCMLA, two orthogonally polarized light field images can be remapped through the functioned imaging sensors. The imaging micro system in conjunction with the electric optical microstructure can be used to perform polarization and light field imaging, simultaneously. Compared with conventional plenoptic cameras using liquid crystal microlens array, the polarization independent light field images with a high image quality can be obtained in the arbitrary polarization state selected. We experimentally demonstrate characters including a relatively wide operation range in the manipulation of incident beams and the multiple imaging modes, such as conventional two dimensional imaging, light field imaging, and polarization imaging. Considering the obvious features of the TN LCMLA, such as very low power consumption, providing multiple imaging modes mentioned, simple and low cost manufacturing, the imaging micro system integrated with this kind of liquid crystal microstructure driven electrically presents the potential capability of directly observing a 3D object in typical scattering media.
author_names: Zhaowei Xin

Dong Wei

Xingwang Xie

Mingce Chen

Xinyu Zhang

Jing Liao

Haiwei Wang

Changsheng Xie
title: Dual polarized light field imaging micro system via a liquid crystal microlens array for direct three dimensional observation.
venue: Optics express
year: 2018

abstract: We propose a new type of lensless camera enabling light field imaging for focusing after image capture and show its feasibilities with some prototyping. The camera basically consists only of an image sensor and Fresnel zone aperture (FZA) Point sources making up the subjects to be captured cast overlapping shadows of the FZA on the sensor, which result in overlapping straight moire fringes due to multiplication of another virtual FZA in the computer. The fringes generate a captured image by two dimensional fast Fourier transform. Refocusing is possible by adjusting the size of the virtual FZA. We found this imaging principle is quite analogous to a coherent hologram. Not only the functions of still cameras but also of video cameras are confirmed experimentally by using the prototyped cameras.
author_names: Takeshi Shimano

Yusuke Nakamura

Kazuyuki Tajima

Mayu Sao

Taku Hoshizawa
title: Lensless light field imaging with Fresnel zone aperture: quasi coherent coding.
venue: Applied optics
year: 2018

abstract: Abstract A microlens array (MLA) is a key optical element for four dimensional light field analysis in a light field camera. MLA manufacturing errors affect light field imaging, but their effects, especially on the physical imaging process and image degradation mechanism, have not entirely been studied. In this paper, we develop a manufacturing error model for MLA and quantitatively analyze raw images and refocused images using image quality evaluation indexes. The results indicate that manufacturing errors cause changes in image features including brightness, resolution, and spot position. The image features undergo changes and the degree of degradation caused by different error types showed great differences.
author_names: Su Li

Yuan Yuan

Li Bin

Fuqiang Wang

Heping Tan
title: Influence of microlens array manufacturing errors on light field imaging
year: 2018

abstract: A major challenge in neuroscience is to sample large scale neuronal activity at high speed and resolution. While calcium (Ca2+ imaging allows high resolution optical read out of neuronal activity, it remains challenging to sample large scale activity at high speed, as most available imaging microscopes provide a trade off between speed and the size of the acquisition volume. One promising method that avoids the trade off between the acquisition rate and volume size is light field microscopy in which the full 3D profile of an object is imaged simultaneously, thereby offering high speed at the cost of reduced spatial resolution. Here we introduce speckle light field microscopy (speckle LFM) which utilizes speckle based structured illumination to enhance spatial resolution. Using speckle LFM we demonstrate brain wide recording of neuronal activity in larval zebrafish at 10 Hz volume rate and at 1.4 times higher resolution compared to conventional light field microscopy and with suppressed background fluorescence. In addition to improving resolution of spatial structure, we show that the increased resolution reduces spurious signal crosstalk between neighboring neurons.
author_names: Michael Taylor

Tobias Nobauer

Alejandro Javier Pernia-Andrade

Friederike Schlumm

Alipasha Vaziri
title: Brain wide 3D light field imaging of neuronal activity with speckle enhanced resolution
year: 2018