Color and spectral analysis of daylight in southern Europe

Hernández‐Andrés, Javier; Romero, Javier; Nieves, Juan Luis; Lee, Raymond L.

doi:10.1364/josaa.18.001325

Cited by 151 publications

(135 citation statements)

References 29 publications

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“…Daylight, civil twilight, and forest spectra An estimate of the variability of daylight and civil twilight spectra (to compare with the variability during twilight and night) was obtained from 2395 daylight, 254 civil twilight and 220 forest measurements of spectral irradiance (Chiao et al, 2000;Hernández-Andrés et al, 2001;Lee and Hernández-Andrés, 2003). All the daylight and 205 of the civil twilight spectra were measured from the roof of the University of Granada's Science Faculty (Granada, Spain, 37°11ЈN 3°35ЈW, elevation 680·m) from February 1996 to February 1998 using a LI-1800 spectroradiometer (LI-COR Bioscience, Lincoln, NE, USA) fitted with a cosine-corrected receptor.…”

Section: Measurement Of Twilight Spectramentioning

confidence: 99%

Crepuscular and nocturnal illumination and its effects on color perception by the nocturnal hawkmoth Deilephila elpenor

Johnsen

Kelber

Warrant

et al. 2006

Journal of Experimental Biology

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SUMMARY Recent studies have shown that certain nocturnal insect and vertebrate species have true color vision under nocturnal illumination. Thus, their vision is potentially affected by changes in the spectral quality of twilight and nocturnal illumination, due to the presence or absence of the moon,artificial light pollution and other factors. We investigated this in the following manner. First we measured the spectral irradiance (from 300 to 700 nm) during the day, sunset, twilight, full moon, new moon, and in the presence of high levels of light pollution. The spectra were then converted to both human-based chromaticities and to relative quantum catches for the nocturnal hawkmoth Deilephila elpenor, which has color vision. The reflectance spectra of various flowers and leaves and the red hindwings of D. elpenor were also converted to chromaticities and relative quantum catches. Finally, the achromatic and chromatic contrasts (with and without von Kries color constancy) of the flowers and hindwings against a leaf background were determined under the various lighting environments. The twilight and nocturnal illuminants were substantially different from each other, resulting in significantly different contrasts. The addition of von Kries color constancy significantly reduced the effect of changing illuminants on chromatic contrast, suggesting that, even in this light-limited environment,the ability of color vision to provide reliable signals under changing illuminants may offset the concurrent threefold decrease in sensitivity and spatial resolution. Given this, color vision may be more common in crepuscular and nocturnal species than previously considered.

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Section: Measurement Of Twilight Spectramentioning

confidence: 99%

Crepuscular and nocturnal illumination and its effects on color perception by the nocturnal hawkmoth Deilephila elpenor

Johnsen

Kelber

Warrant

et al. 2006

Journal of Experimental Biology

Self Cite

199

250

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“…In assessing the performance of the algorithm, Munsell [11], floral [12], and measured daylight [13] have been used. The measured daylight spectra are available for wavelengths between 300 and 1100 nm [13].…”

Section: Extraction Of Illuminant-invariant Reflectance Featuresmentioning

confidence: 99%

“…The measured daylight spectra are available for wavelengths between 300 and 1100 nm [13]. As described by Ratnasingam and Collins [7], two sets of 146 spectra have been chosen from these measured daylight spectra.…”

Section: Extraction Of Illuminant-invariant Reflectance Featuresmentioning

confidence: 99%

Extending “color constancy” outside the visible region

2011

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In this paper, the results of an investigation of the possibility of extending "color constancy" to obtain illuminantinvariant reflectance features from data in the near-ultraviolet (UV) and near-infrared (IR) wavelength regions are reported. These features are obtained by extending a blackbody-model-based color constancy algorithm proposed by Ratnasingam and Collins [J. Opt. Soc. Am. A 27, 286 (2010)] to these additional wavelengths. Ratnasingam and Collins applied the model-based algorithm in the visible region to extract two illuminant-invariant features related to the wavelength-dependent reflectance of a surface from the responses of four sensors. In this paper, this modelbased algorithm is extended to extract two illuminant-invariant reflectance features from the responses of sensors that cover the visible and either the near-UV or near-IR wavelength. In this investigation, test reflectance data sets are generated using the goodness-fitness coefficient (GFC). The appropriateness of the GFC for generating the test data sets is demonstrated by comparing the results obtained with these data with those obtained from data sets generated using the CIELab distance. Results based upon the GFC are then presented that suggest that the modelbased algorithm can extract useful features from data from the visible and near-IR wavelengths. Finally, results are presented that show that, although the spectrum of daylight in the near UV is very different from a blackbody spectrum, the algorithm can be modified to extract useful features from visible and near-UV wavelengths.

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“…Other patches are open, but will only receive direct sunlight for a small part of the day when the sun is overhead, at other times being lit only by skylight. Furthermore, the spectral content of sunlight and light from the sky varies over the course of the day and between days (Hernández- Andrés et al, 2001;Johnsen et al, 2006). …”

Section: Introductionmentioning

confidence: 99%

Illumination preference, illumination constancy and colour discrimination by bumblebees in an environment with patchy light

Arnold

Chittka

2012

Journal of Experimental Biology

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SUMMARYPatchy illumination presents foraging animals with a challenge, as the targets being sought may appear to vary in colour depending on the illumination, compromising target identification. We sought to explore how the bumblebee Bombus terrestris copes with tasks involving flower colour discrimination under patchy illumination. Light patches varied between unobscured daylight and leaf-shade, as a bee might encounter in and around woodland. Using a flight arena and coloured filters, as well as one or two different colours of artificial flower, we quantified how bees chose to forage when presented with foraging tasks under patchy illumination. Bees were better at discriminating a pair of similar colours under simulated unobscured daylight illumination than when foraging under leaf-shade illumination. Accordingly, we found that bees with prior experience of simulated daylight but not leaf-shade illumination initially preferred to forage in simulated daylight when all artificial flowers contained rewards as well as when only one colour was rewarding, whereas bees with prior experience of both illuminants did not exhibit this preference. Bees also switched between illuminants less than expected by chance. This means that bees prefer illumination conditions with which they are familiar, and in which rewarding flower colours are easily distinguishable from unrewarding ones. Under patchy illumination, colour discrimination performance was substantially poorer than in homogenous light. The beesʼ abilities at coping with patchy light may therefore impact on foraging behaviour in the wild, particularly in woodlands, where illumination can change over short spatial scales.

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Color and spectral analysis of daylight in southern Europe

Cited by 151 publications

References 29 publications

Crepuscular and nocturnal illumination and its effects on color perception by the nocturnal hawkmoth Deilephila elpenor

Crepuscular and nocturnal illumination and its effects on color perception by the nocturnal hawkmoth Deilephila elpenor

Extending “color constancy” outside the visible region

Illumination preference, illumination constancy and colour discrimination by bumblebees in an environment with patchy light

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