Abstract
In this paper, a prototyped plenoptic camera based on a key electrically tunable liquid-crystal (LC) device for all-in-focus polarimetric imaging is proposed. By using computer numerical control machining and 3D printing, the proposed imaging architecture can be integrated into a hand-held prototyped plenoptic camera so as to greatly improve the applicability for outdoor imaging measurements. Compared with previous square-period liquid-crystal microlens arrays (LCMLA), the utilized hexagonal-period LCMLA has remarkably increased the light utilization rate by ~15%. Experiments demonstrate that the proposed imaging approach can simultaneously realize both the plenoptic and polarimetric imaging without any macroscopic moving parts. With the depth-based rendering method, both the all-in-focus images and the all-in-focus degree of linear polarization (DoLP) images can be obtained efficiently. Due to the large depth-of-field advantage of plenoptic cameras, the proposed camera enables polarimetric imaging in a larger depth range than conventional 2D polarimetric cameras. Currently, the raw light field images with three polarization states including I0 and I60 and I120 can be captured by the proposed imaging architecture, with a switching time of several tens of milliseconds. Some local patterns which are selected as interested target features can be effectively suppressed or obviously enhanced by switching the polarization state mentioned. According to experiments, the visibility in scattering medium can also be apparently improved. It can be expected that the proposed polarimetric imaging approach will exhibit an excellent development potential.
Highlights
To describe the transmission characteristics of light waves in 3D space, fully 3D or “integral” photography was first introduced by Lippmann [1]
We demonstrate an integrated plenoptic camera based on an electrically tunable LC device for all-in-focus polarimetric imaging
The inner side of the top and bottom glass substrates is deposited with a planar indium tin oxide (ITO) electrode of 185 nm thickness, respectively, and the middle glass substrate is deposited with a planar ITO electrode of 50 nm thickness on both sides, according to common magnetron sputtering
Summary
To describe the transmission characteristics of light waves in 3D space, fully 3D or “integral” photography was first introduced by Lippmann [1]. In 1991, Adelson and Bergen proposed a 7D function to represent the spatial distribution of geometric light beams, which was called the plenoptic function [3]. In the case of neglecting attenuation of light waves during transmission, the 5D plenoptic function can be simplified to 4D, which can be parametrically characterized with two parallel planes. Based on the basic light field rendering methods, Ng et al built the first hand-held plenoptic camera by directly inserting a microlens array between the main lens system and the imaging sensors in 2005, which was already called the standard plenoptic camera [6]. In 2009, Lumsdaine and Georgiev further proposed a kind of focused plenoptic camera, which can be used to obtain a much higher spatial resolution of the rendering images [7]. Compared with conventional cameras, plentopic cameras have a larger depth of field [6,7,8]
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