Robust sky light polarization detection with an S-wave plate in a light field camera

Abstract

The sky light polarization navigator has many advantages, such as low cost, no decrease in accuracy with continuous operation, etc. However, current celestial polarization measurement methods often suffer from low performance when the sky is covered by clouds, which reduce the accuracy of navigation. In this paper we introduce a new method and structure based on a handheld light field camera and a radial polarizer, composed of an S-wave plate and a linear polarizer, to detect the sky light polarization pattern across a wide field of view in a single snapshot. Each micro-subimage has a special intensity distribution. After extracting the texture feature of these subimages, stable distribution information of the angle of polarization under a cloudy sky can be obtained. Our experimental results match well with the predicted properties of the theory. Because the polarization pattern is obtained through image processing, rather than traditional methods based on mathematical computation, this method is less sensitive to errors of pixel gray value and thus has better anti-interference performance.

Review of visualization methods for passive polarization imaging

“…While there are some good examples 4,12,13 of the use of effective colormaps used in polarization, the vast majority of colormaps used are either the rainbow colormap, [14][15][16][17] which has been theoretically [18][19][20] and experimentally 21 shown to be ineffective for most analysis tasks, or a colormap inappropriate for the data structure. [22][23][24] Both reviews by Zhou and Hansen 25 and Bernard et al 26 provide a general review of colormaps in visualization.…”

Mining the Smartness of Insect Ultrastructures for Advanced Imaging and Illumination

“…In addition, ACE provides various optical properties: a wide FOV, fast motion sensitivity, and polarization sensitivity. Thanks to advanced microelectromechanical system (MEMS) fabrication technologies, various ACE structures including planar arrays, curved arrays, and micropolarizer are recently accomplished ( Figure ). Many studies of planar ACE structures have been performed to directly mount the ACE on the CMOS or CCD image sensors.…”

“…Navigation sensors based on a sky light polarization exhibit many advantages but a weak light intensity due to the clouds degrades the performance and accuracy of navigation sensors. To solve the low intensity of light, Zhang et al proposed a novel method and structure depending on the polarization pattern of sky light in a snapshot captured by a light field camera with a radial polarizer as well as the polarization degree as a function of image brightness (Figure i). This method measures the degree of polarization even in the cloudy condition because it is less sensitive to the errors of gray value pixels.…”

“…Copyright 2008, Elsevier. i) Polarizer in light field camera, Reproduced with permission . Copyright 2016, OSA Publishing.…”

“…Since 2006, the hemispherical microlens array‐type compound eyes have been widely exploited for man‐made imaging technologies, ranging from fill‐factor enhancement of CMOS and CCD imaging sensors to a compact optical system, along with remarkable advances of micro‐ and nanofabrication techniques . Insect compound eyes have versatile photonic properties, for example, wide field‐of‐view (FOV), negligible distortion, low aberration, and deep depth‐of‐field as well as highly efficient light focusing and guiding, largely exploited for optical color sensing, advanced medical imaging, virtual reality, 3D imaging, light field cameras, robotic systems, security including surveillance and collision‐free navigation of terrestrial and aerospace vehicles . Recently, multilevel and hierarchical fabrications incorporating micro‐ and nanostructures have been developed to reproduce distinguished properties observed in nature.…”