Illumination invariance and shadow compensation via spectro-polarimetry technique

Abstract

A major problem for obtaining target reflectance via hyperspectral imaging systems is the presence of illumination and shadow effects. These factors are common artefacts, especially when dealing with a hyperspectral imaging system that has sensors in the visible to near infrared region. This region is known to have highly scattered and diffuse radiance which can modify the energy recorded by the imaging system. Shadow effect will lower the target reflectance values due to the small radiant energy impinging on the target surface. Combined with illumination artefacts, such as diffuse scattering from the surrounding targets, background or environment, the shape of the shadowed target reflectance will be altered. In this study we propose a new method to compensate for illumination and shadow effects on hyperspectral imageries by using a polarization technique. This technique, called spectropolarimetry, estimates the direct and diffuse irradiance based on two images, taken with and without a polarizer. The method is evaluated using a spectral 2 similarity measure, angle and distance metric. The results of indoor and outdoor tests have shown that using the spectro-polarimetry technique can improve the spectral constancy between shadow and full illumination spectra.

Impact of varying irradiance on vegetation indices and chlorophyll fluorescence derived from spectroscopy data

“…The illumination correction method implemented in the current ATCOR-4 model (Richter & Schläpfer, 2014) combines DEMs and an empirical model to quantify relative amounts of E dif and E dir at pixel level, which are used afterwards in the atmospheric correction. Ibrahim et al (2012) use an alternative concept called spectro-polarimetry to estimate relative amounts of E dif and E dir at pixel level, but this requires at least two observations with and without a polarizer, which is not practical for airborne observations. The ToA approach, as for example proposed by Laurent et al (2011a, b), provides a flexible framework to estimate and incorporate improved descriptive data and to account for illumination effects strictly following underlying physics.…”

Adaptive processing of catadioptric images using polarization imaging: towards a pola-catadioptric model

“…The comparison between the classical Harris algorithm [Eq. (11)] and the adapted one [Eq. (12)] is illustrated in Fig.…”

“…In the last decades, thanks to its richness in information, the polarization concept has been strongly explored to analyze, interpret, or process several types of images. [8][9][10][11] This paper aims, by using the polarization imaging, to propose a generic solution for the catadioptric images processing. The proposed method provides an efficient model to define an accurate neighborhood around each pixel within the catadioptric plane.…”

Per-Norm Based Automotive Headlamp Detection in Hypersepctral Image for Visible Light Communication

“…Normalized technique are used to solve problems generated by different spectral profiles at the same material due to shading and shadow effects [11]. The most common technique is a normalized mean-centered normalization (Mean-Norm) method [12].…”