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Color fundamentals for digital imaging
Published in Sharma Gaurav, Digital Color Imaging Handbook, 2017
Spectroradiometers can be used to measure both self-luminous and reflective objects. For the measurement of reflectance spectra, a spectrally smooth (preferably, white) light source and a spectrally referenced sample (preferably, white) are required. Comparison measurements between the known sample and the sample under question are made under identical conditions, allowing the determination of the unknown sample’s reflectance spectrum, from which the color descriptor under any viewing illuminant can be obtained. Normally, the exact spectrum of the illuminant used with the spectroradiometer in the reflectance measurement is immaterial, provided it has sufficient power over the spectral range of interest. However, for the measurement of fluorescent materials, the power in the ultraviolet regions is also important, and the illuminant must closely approximate the desired standard illuminant under which colors are to be computed.347
Light Sources
Published in Toru Yoshizawa, Handbook of Optical Metrology, 2015
This method of grading of colorimetric shifts obtained in test samples is called CIE test-color method, and is applicable for light sources that have chromaticity close to the reference illuminant. The CRI is a measure of how well balanced the different color components of white light are. A standard reference illuminant has a general CRI Ra = 100. The two primary standard illuminants are the CIE Standard Illuminant A (representative of tungsten-filament lighting with color temperature of 2856 K) and the CIE Standard Illuminant D65 (representative of average daylight with color temperature of 6500 K). Color rendering is a very important property of cold illuminants such as LEDs and discharge lamps, whose emission spectrum contains certain wavelengths. More information about the test-color samples, standard colorimetric illuminants and observers, and CRIs can be found in related references [3,5,24,45] and CIE reports [47–50], as well as in the literature on LEDs [9–11].
Measurements
Published in J. R. Coaton, A. M. Marsden, Lamps and Lighting, 2012
Illuminance meters are usually calibrated using a tungsten lamp operated at a colour temperature of 2856 K (i.e. CIE Standard Illuminant A). When a meter is used for measurements with other light sources, it may be necessary to correct the indicated reading. The magnitude of the correction will depend on the difference between the spectral power distributions of the calibration source and the other light source in question, and on the relative spectral sensitivity of the photometer head (i.e. the deviation from the V(λ) curve). BS 667 (BSI 1996) defines the requirements for two types of portable illuminance meter and requires that correction factors for common discharge lamps shall be supplied.
Estimation of daylight availability in Kolkata and approximation of indoor daylight levels for different daylighting methods
Published in International Journal of Sustainable Energy, 2022
Sourin Bhattacharya, Sudipta Majumder, Subarna Roy, Imran Hossain Sardar
Daylight is considered to be the best source of illumination for colour rendering, it can provide 110 lumens of luminous flux per Watt of solar radiation (a luminous efficacy of 110 lm/W) and its spectra closely match the human spectral visual response (Kandilli and Ulgen 2008). However, the luminous efficacy of daylight varies with sky clearness, solar altitude and atmospheric conditions. It is 70–105 lm/W for direct sunlight, approximately 130 lm/W for the clear sky and around 110 lm/W for the overcast sky under diffuse skylight (Littlefair 1985). Furthermore, daylight is a natural, temporally variant (Ferenčíková and Darula 2017), dynamic source of illumination (Deroisy and Deneyer 2017) and its spectral power distribution (SPD) for the 330 –700 nm wavelength range was measured by Henderson and Hodgkiss (1963). The CIE Standard Illuminant D65 is a hypothesised illuminant to simulate the naturally occurring standard illumination conditions under daylight and attempts have been made to design and simulate the D65 (Powell 1996; Lam and Xin 2002). Moreover, the human circadian clock is entrained to sunlight or more specifically the 24-h solar cycle (Duffy and Wright Jr 2005; Roenneberg et al. 2013; Woelders et al. 2017) and exposure to daylight assumes much importance in the everyday life of human beings since human health and wellness are intricately linked to it and various studies have indicated that daylight is preferred to artificial illumination in different settings or fields of human activity (Markus 1967; Cuttle 1983; Heerwagen and Heerwagen 1986; Galasiu and Veitch 2006).
Effect of high-humidity hot air impingement blanching (HHAIB) and drying parameters on drying characteristics and quality of broccoli florets
Published in Drying Technology, 2019
Zi-Liang Liu, Jun-Wen Bai, Wen-Xia Yang, Jun Wang, Li-Zhen Deng, Xian-Long Yu, Zhi-An Zheng, Zhen-Jiang Gao, Hong-Wei Xiao
In current work, the color of fresh and dried samples under different conditions was measured using a colorimeter (Minolta Chroma, CR-400, Japan) following the method described by Wang et al.[34] with modification. The fresh and dried samples with less stems were crushed, and placed into Petri dishes before measuring. Care was taken to assure there was no gap between the sample and the Petri dish lid. And the calibration was performed by placing the tip of measuring head flat against the surface of the white calibration place before measuring. A CIE standard illuminant D65 and observer 10° were used to determine CIE LAB color space coordinates, L* (lightness), a* (redness/greenness), and b* (yellowness/blueness). Besides, total color difference (ΔE), hue angle (H0), and browning index (BI) was calculated from the value of L*, a*, b* using Equations (3)–(6).[34,35] Six replicate measurements for each sample were calculated and then the average values of color parameters were obtained. where where, L*, a*, and b* represent color values of treated broccoli floret samples, L0*, a0*, and b0* are the color parameters of fresh ones.
Color prediction of mushroom slices during drying using Bayesian extreme learning machine
Published in Drying Technology, 2020
Zi-Liang Liu, Feng Nan, Xia Zheng, Magdalena Zielinska, Xu Duan, Li-Zhen Deng, Jun Wang, Wei Wu, Zhen-Jiang Gao, Hong-Wei Xiao
The surface color of mushroom slices was measured by a colorimeter (SMY-2000ST, Shengmingyang Co., Beijing, China). A CIE standard illuminant D65 and observer 10° were used to determine CIELAB color space coordinates, such as L* (lightness), a* (redness/greenness), and b* (yellowness/blueness). The calibration test was performed by placing the tip of measuring head flat against the surface of the white calibration plate. All of the color measurement for each sample were taken sextuplicate.