Color analysis CIELAB

UV/VIS The topic of colorants and color analysis was introduced in the previous chapter textiles represent one of the most important forensic applications of colorant chemistry and analysis. Colorant analysis and comparison and the use of chromaticity coordinates were discussed in detail in the previous chapter all are applicable to fibers. The plotting of CIELAB coordinates is useful in comparing colors and shades. Some fibers are metameiic, meaning that their color will appear different under different Uluminants. Textiles are often designed to have this property. Metameric fibers perceived as being the same color are distinguished by different UV/VIS spectra. 

The spectrum of red wines has a maximum at 520 nm, due to anthocyanins and their flavylium combinations, and a minimum in the region of 420 nm. Color intensity and hue, as defined by Sudrand (1958), only take into account the con-tribntions of red and yellow to overall color. Of conrse, the resnlts of this partial analysis cannot claim to reflect the overall visual perception of a wine s color. Application of the CIELAB universal color appreciation system, proposed by the International Commission on Illumination, certainly represents an improvement, but the results are difficult for winemakers to interpret. 

Spectrophotometers can measure the spectral reflection of a sample and represent it graphically by means of computer peripherals. Spectrophotometers are a useful aid in the analysis and synthesis of color samples. All colorimeters enable calculation of the total color difference with the CIELAB color difference formula. 

Eq. 3-3), a concept introduced in Section 3.1.5 in the context of cluster analysis. This technique, introduced in 1976, uses the tristimulus values X, Y, and Z as inputs and converts these to the corresponding L, a, and b coordinates in the uniform color space. The distance between two points in the CIELAB system can be calculated as ... 

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