Separation and contrast enhancement of overlapping cast shadow components using polarization

Abstract

Shadow is an inseparable aspect of all natural scenes. When there are multiple light sources or multiple reflections several different shadows may overlap at the same location and create complicated patterns. Shadows are a potentially good source of information about a scene if the shadow regions can be properly identified and segmented. However, shadow region identification and segmentation is a difficult task and improperly identified shadows often interfere with machine vision tasks like object recognition and tracking. We propose here a new shadow separation and contrast enhancement method based on the polarization of light. Polarization information of the scene captured by our polarization-sensitive camera is shown to separate shadows from different light sources effectively. Such shadow separation is almost impossible to realize with conventional, polarization-insensitive imaging. CommentsCopyright 2006 Abstract: Shadow is an inseparable aspect of all natural scenes. When there are multiple light sources or multiple reflections several different shadows may overlap at the same location and create complicated patterns. Shadows are a potentially good source of information about a scene if the shadow regions can be properly identified and segmented. However, shadow region identification and segmentation is a difficult task and improperly identified shadows often interfere with machine vision tasks like object recognition and tracking. We propose here a new shadow separation and contrast enhancement method based on the polarization of light. Polarization information of the scene captured by our polarization-sensitive camera is shown to separate shadows from different light sources effectively. Such shadow separation is almost impossible to realize with conventional, polarization-insensitive imaging.

Matrix Structure of Metamaterial Absorbers for Multispectral Terahertz Imaging

“…Hence, the polarization direction of the incident linear polarized radiation at 0.33 THz can be determined by comparing signal intensities of orthogonally oriented pixels. Polarization difference imaging technique can facilitate detection and feature extraction of targets in scattering or reflecting media (see, for example, works [28][29][30][31] and references there).…”

Polarization image sensors: Learning from biology to make the invisible visible

“…In [18,19], polarization was used to significantly increase the visibility length in optically scattering media. In [22,23], the polarization filters convert a beam of unpolarized or mixed polarization electromagnetic light into a well-defined linear polarized beam of light. By including the polarization detection, the study in paper [22] and shown in Fig.1 illustrates latent fingerprint images extracted without using any powder or chemicals on the object.…”

“…By including the polarization detection, the study in paper [22] and shown in Fig.1 illustrates latent fingerprint images extracted without using any powder or chemicals on the object. Another paper describes how to improve visibility in shadows using the polarization characteristics of reflected light [23]. The proposed shadow separation is impossible to realize in a polarizationblind imaging system as shown in Fig.2.…”

“…A polarization sensitive image system is also useful in improving the image quality while sensing under optically scattered environments, such as underwater [17], or foggy conditions [18,19]. Previous work also showed a great potential of polarization in remote sensing [20,21], fingerprint detection [22], and sensing object illuminated by low intensity light source [23] as will be illustrated in the following section.…”

High linearly polarized light emission from InGaN light-emitting diode with multilayer dielectric/metal wire-grid structure

“…One of the features is the polarized light emission, which is highly desirable for many applications, e.g., flat panel display 4 and imaging. 5 Several authors reported the polarized light emission from LED structures grown on nonpolar [6][7][8][9] or semipolar GaN substrates. 10 For example, Tsujimura et al 7 measured a polarization ratio (PR) of 0.8 (or equivalent extinction ratio (ER) of 9.5 dB) from m-plane InGaN-based LEDs.…”