Light field

About: Light field is a research topic. Over the lifetime, 5357 publications have been published within this topic receiving 87424 citations.

On the resolution of plenoptic PIV

Abstract: Plenoptic PIV offers a simple, single camera solution for volumetric velocity measurements of fluid flow. However, due to the novel manner in which the particle images are acquired and processed, few references exist to aid in determining the resolution limits of the measurements. This manuscript provides a framework for determining the spatial resolution of plenoptic PIV based on camera design and experimental parameters. This information can then be used to determine the smallest length scales of flows that are observable by plenoptic PIV, the dynamic range of plenoptic PIV, and the corresponding uncertainty in plenoptic PIV measurements. A simplified plenoptic camera is illustrated to provide the reader with a working knowledge of the method in which the light field is recorded. Then, operational considerations are addressed. This includes a derivation of the depth resolution in terms of the design parameters of the camera. Simulated volume reconstructions are presented to validate the derived limits. It is found that, while determining the lateral resolution is relatively straightforward, many factors affect the resolution along the optical axis. These factors are addressed and suggestions are proposed for improving performance.

Distance measurement based on light field geometry and ray tracing

Abstract: In this paper, we propose a geometric optical model to measure the distances of object planes in a light field image. The proposed geometric optical model is composed of two sub-models based on ray tracing: object space model and image space model. The two theoretic sub-models are derived on account of on-axis point light sources. In object space model, light rays propagate into the main lens and refract inside it following the refraction theorem. In image space model, light rays exit from emission positions on the main lens and subsequently impinge on the image sensor with different imaging diameters. The relationships between imaging diameters of objects and their corresponding emission positions on the main lens are investigated through utilizing refocusing and similar triangle principle. By combining the two sub-models together and tracing light rays back to the object space, the relationships between objects' imaging diameters and corresponding distances of object planes are figured out. The performance of the proposed geometric optical model is compared with existing approaches using different configurations of hand-held plenoptic 1.0 cameras and real experiments are conducted using a preliminary imaging system. Results demonstrate that the proposed model can outperform existing approaches in terms of accuracy and exhibits good performance at general imaging range.

Structure of light fields in natural scenes

Abstract: Light fields [J. Math. Phys. 18, 51 (1936) ;The Photic Field (MIT, 1981)] of natural scenes are highly complex and vary within a scene from point to point. However, in many applications complex lighting can be successfully replaced by its low-order approximation [J. Opt. Soc. Am. A 18, 2448 (2001); Appl. Opt. 46, 7308 (2007)]. The purpose of this research is to investigate the structure of light fields in natural scenes.We describe the structure of light fields in terms of spherical harmonics and analyze their spatial variation and qualitative properties over scenes. We consider several types of natural scene geometries. Empirically and via modeling, we study the typical behavior of the first- and second-order approximation of the local light field in those scenes. The first-order term is generally known as the “light vector” and has an immediate physical meaning. The quadrupole component, which we named “squash tensor,” is a useful addition as we show in this paper. The measurements were done with a custom-made device of novel design, called a “Plenopter,” which was constructed to measure the light field in terms of spherical harmonics up to the second order. In different scenes of similar geometries, we found structurally similar light fields, which suggests that in some way the light field can be thought of as a property of the geometry. Furthermore, the smooth variation of the light field’s low-order components suggests that, instead of specifying the complete light field of the scene, it is often sufficient to measure the light field only in a few points and rely on interpolation to recover the light field at arbitrary points of the scene.

Improved performance of HgCdTe infrared detector focal plane arrays by modulating light field based on photonic crystal structure

Abstract: An HgCdTe long-wavelength infrared focal plane array photodetector is proposed by modulating light distributions based on the photonic crystal. It is shown that a promising prospect of improving performance is better light harvest and dark current limitation. To optimize the photon field distributions of the HgCdTe-based photonic crystal structure, a numerical method is built by combining the finite-element modeling and the finite-difference time-domain simulation. The optical and electrical characteristics of designed HgCdTe mid-wavelength and long-wavelength photon-trapping infrared detector focal plane arrays are obtained numerically. The results indicate that the photon crystal structure, which is entirely compatible with the large infrared focal plane arrays, can significantly reduce the dark current without degrading the quantum efficiency compared to the regular mesa or planar structure.