Spectral reflectance curves

Fig. 4 Explanation of the fluorescence-quenching effect [2]. — (A) chromatograms of the same quantities of saccharin and dulcin observed under UV 254 light, (B) schematic representation of fluorescence quenching, (C) spectral reflectance curves of saccharin and dulcin.

Two objects with different spectral properties, i.e., variation in the slope of spectral reflectance curve of two bands, can be separable with the help of ratio images (Lillesand et al. 2007). In this study standard reflectance data of USGS Spectral Library and John Hopkins University spectral library (Available in ENVI) have been used. To enhance the dissimilarity between different rock types in the scene, plots with a higher reflectance were kept in the numerator and plots with low reflectance were kept in the denominator, while taking the band ratios. Using this approach, a ratio of 5/3 was taken for basalt, 7/3 for peridotite, and 4/2 for vegetation. 

Figure 3. Spectral reflectance curves of some inorganic pigments in paints...

Pigments and coatings may be unambiguously characterized by their spectral reflectance curves q (A) or spectral reflectance factor curves / ( ) (Fig. 3). The reflectance spectrum q (A) or R (A) and hence the color properties can be almost completely derived from physical quantities [1.15] (Fig. 4) ... 

Figure 19. Spectral reflectance curves of barium sulfate and zinc sulfide a) Barium sulfate b) Zinc sulfide (Codoped)...

Figure F5.1.4 The spectral reflectance curve of a red object plots reflectance at each wavelength. Figure courtesy of GretagMacbeth. This black and white facsimile of the figure is intended only as a placeholder for full-color version of figure go to http //www.currentprotocols.com/colorfigures...

Spectral reflectance curves for the range of meteorite types are illustrated in fig. 10.12. These spectra demonstrate the diagnostic features of the various... 

COHEN J (1964) Dependency of the spectral reflectance curves of the Munsell Color Chips, Psych. Sci., 1. 

After calculation, the best approximation to the desired spectral reflectance curve and the required optical or physical thickness of the individual films in correct sequence forming the system are printed out. 

Figure 27 shows the spectral reflectance curve of a broadband laser mirror. 

Figure 2. Spectral reflectance curves for 3 colors of rigid vinyl.

Figure 3.10 Spectral reflectance curves for control and plasma-treated nylon 6 fibers with different moisture regains (a) acid dye and (b) dispersive dye (Zhu et al., 2007, Wang and Qiu, 2007).

Metameric Colours. Colours that appear to be the same under one type of illuminant but, because they have different spectral reflectivity curves, will not match under a different illuminant. Two white vitreous enamels may be metameric, for example, if one is opacified with titania in the anatase form whereas the other contains titania in the form of rutile. Methuselah. A 9-quart wine bottle. Methylene Blue Index A simple approximate method for assessing the surface area of a clay. O.OIM methylene blue dye is added to aqueous suspension of clay, in successive small amounts, to determine the least amount of dye required to impart colour to the water suspending the clay. Dye up to this amount is absorbed by the clay, so that this is a measure of the clay s cation exchange capacity (see ionic exchange). For most pottery clays this is proportional to the surface area to a good approximation. ASTM C837 specifies a test for clays. 

Optical properties and spectral reflection curves of P.Y. 185 and P.Y. 139 in an alkyd / melamine system at a constant pigment / Ti02 ratio of 1 10 are shown in Figure 14-13 ... 

As seen from Figure 4, it is observed that the spectral reflectance curves of SPT II, SPT IE and SPT IV are clearly differentiated. Using multiple linear regression analysis (Eq. 5) obtained from the proposed skin pigment model, we can estimate the concentration of pheomelanin and eumelanin. Figures 5 and 6 show the estimated pheomelanin and eumelanin from each participant. 

For color development work, a colorimeter that provides the tristimulus value and calculates the color difference is simply not enough. A more sophisticated instrument such as a spectrophotometer is generally required. A spectrophoto-meter, when used with a chart recorder or CRT, provides a complete spectral reflectance curve covering the entire range of the visible spectrum from 380 to 700 nm. Additionally, it provides the percentage reflectance value at each 20-nm interval and computes the tristimulus values, chromaticity coordinates, and color difference values. 

There have been many new developments in color measurement systems technology in recent years. A major breakthrough is in the area of portable color measurement techniques. Newly developed portable spectrophotometers (Figure 6-13h) now make it possible to measure and analyze data on the production floor. Some portable spectrophotometers are also capable of displaying an actual spectral reflectance curve. Bench-top spectrophotometers have been updated to allow more computer control of the lens, UV filter, and specular port. The ability to calibrate the UV component of the color spectrum is an important feature for measuring fluorescent colors accurately. Advances in windows-based software has improved the capabilities for statistical analysis of color measurements, color corrections, and color formulation. 

Figure 6-13. (a) A typical spectral reflectance curve. (Courtesy of Gretag Macbeth.) (b) A portable spectrophotometer. (Courtesy of Datacolor.)... 

The arrangement of Fig. 10 ensures that all components of diffusely reflected light are equally weighted and that the specular component can be included in or eliminated from the measurement. Often, however, there is no true specular component, but rather a high-intensity lobe with a definite spread. This renders somewhat arbitrary the distinction between the specular and diffuse components. Operationally, the distinction depends on the size of exit port chosen for the specular light trap. Reflectance measurements are usually scaled relative to what a perfectly diffuse, totally reflecting surface would produce if located in the position of the sample. Figure 11 shows the diffuse spectral reflectance curves of a set of enamel paints that are sometimes used as calibration standards. 

The spectral reflectance curve of a surface can readily be compared with the ideal curve to give a visual indication of spectral selectivity. Figure 4 shows the the reflectance of the ideal solar photothermal absorber with the transition at 2 pm. The reflectance curve for silver is also included. Silver reaches a maximum reflectance of about 0.985 in the long-wavelength region, thus placing a practical limit on longwave reflectance of a solar absorber. 

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