Simple and effective calculations about spectral power distributions of outdoor light sources for computer vision

Abstract

Abstract:The Spectral Power Distributions (SPD) of outdoor light sources are not constant over time and atmospheric conditions, which causes the appearance variation of a scene and common natural illumination phenomena, such as twilight, shadow, and haze/fog. Calculating the SPD of outdoor light sources at different time (or zenith angles) and under different atmospheric conditions is of interest to physically-based vision. In this paper, for computer vision and its applications, we propose a feasible, simple, and effective SPD calculating method based on analyzing the transmittance functions of absorption and scattering along the path of solar radiation through the atmosphere in the visible spectrum. Compared with previous SPD calculation methods, our model has less parameters and is accurate enough to be directly applied in computer vision. It can be applied in computer vision tasks including spectral inverse calculation, lighting conversion, and shadowed image processing. The experimental results of the applications demonstrate that our calculation methods have practical values in computer vision. It establishes a bridge between image and physical environmental information, e.g., time, location, and weather conditions.

Hyperspectral environmental illumination maps: Characterizing directional spectral variation in natural environments

“…Other studies show similar statistical trends where the chromaticites of natural illuminants cluster closely around the daylight locus [3]. It is also well understood how the spectrum of daylight can change over time and atmospheric conditions [4]. In addition, recent work has expanded these observations to twilight [5].…”

Spectral measurement of daylights and surface properties of natural objects in Japan

“…The weather was mainly sunny on 2013/11/20 and 2013/12/24 and mostly cloudy on the other two days. The campus is located in an urban city near the capital of Japan, and thus measured daylight may include the influence of air pollution, for example the nitrogen dioxide which is known to absorb short wavelength light [ 1 ].…”

“…The self-rotation of the Earth creates a 24-hour cycle within a day which periodically alters color and intensity of daylights reaching the earth’s surface. Atmospheric conditions such as cloud cover, air pollution, haze or fog modify the spectral composition of daylight [ 1 ]. Furthermore, the tilt of the Earth’s self-rotation axis creates a variation in the length of the daylight period across seasons and geographical locations, suggesting that understanding daylight spectra requires comprehensive measurements in spectral, temporal, and spatial domains across diverse cities and countries.…”

The Effect of Light Distribution of LED Luminaire on Human Ocular Physiological Characteristics

“…and light distribution (illuminance uniformity [17], [18]). For a luminaire, optical performances on light quality and glare are applicable, such as illuminance, luminance, correlated color temperature (CCT) [19], [20], and spectra power distribution (SPD) [21], [22].The light distribution index is uncommon for luminaire products but often employed in indoor lighting. These optical indices could cover the overall characteristics of lighting environment, and there are corresponding standards for assessments, most of which are based on subjective perception of discomfort.…”