Spatial–Spectral Evidence of Glare Influence on Hyperspectral Acquisitions

Abstract

Glare is an unwanted optical phenomenon which affects imaging systems with optics. This paper presents for the first time a set of hyperspectral image (HSI) acquisitions and measurements to verify how glare affects acquired HSI data in standard conditions. We acquired two ColorCheckers (CCs) in three different lighting conditions, with different backgrounds, different exposure times, and different orientations. The reflectance spectra obtained from the imaging system have been compared to pointwise reference measures obtained with contact spectrophotometers. To assess and identify the influence of glare, we present the Glare Effect (GE) index, which compares the contrast of the grayscale patches of the CC in the hyperspectral images with the contrast of the reference spectra of the same patches. We evaluate, in both spatial and spectral domains, the amount of glare affecting every hyperspectral image in each acquisition scenario, clearly evidencing an unwanted light contribution to the reflectance spectra of each point, which increases especially for darker pixels and pixels close to light sources or bright patches.

Film and Digital Media: Open Issues and Novel Approaches for Digital Color Film Restoration

“…In the literature, we can find several works where glare has been measured in digital imaging domain before imaging acquisition [6], [7] and in postproduction [8]. Furthermore, some publications in imaging domain try to measure glare in different imaging systems, like micro computed tomography [9], radiographies [10], satellite imaging [11], cameras [12] and hyperspectral imaging [13]. Unfortunately, in film restoration there are few accessible publications relating to this major issue and restoration specialists cannot rely on published and open-source systematic testing and measurements of scanning systems.…”

Complex process of image color correction: a test of a target-based framework

“…Table 13 reports the Glare Evidence (GE) proposed by [4] and defined as follows: Glare is rarely considered in color correction practices, but its magnitude is usually too high to be ignored. One of the goals of this paper is underlining this effect.…”

“…Among the many factors that affect the acquisition of a scene, lens glare is the one usually responsible of the biggest departure [2]. Even if rarely measured, the difference introduced by glare can easily exceed 100 % in the dark areas [1,2,3,4]. Its characteristic is to affect areas differently, following also their mutual spatial distribution.…”

The limits of colorimetry in cultural heritage applications

“…The main flaws occur in the transmission of frequencies, in the formation of glare noise and aberrations 42 . Unfortunately, glare is always present in the acquisition systems and this produces an unwanted loss of contrast and information 43 . As a consequence, the simple pointwise colorimetry can not overcome the limit imposed by the instruments and the problem of a correct image acquisition is still open, in particular considering solutions for glare.…”