OptLab-UW/SPX    CIE Color Measurement Calculations

Color calculations are employed to describe the color of transparent and reflective samples in an objective way. As a starting point the transmission or reflection spectrum of the sample in the visible range is used. With this spectrum the process of human color vision is mathematically copied with standardized data sets; as a result a set of 3 values is generated, which describe the color of a sample objectively and definitely. The calculation process uses the illumination and angle of vision. Since these parameters influence the resulting data triplet, they must be given for each set of color values. Originally these procedures were defined by CIE, but have now found their way into many national and international standards like DIN 5033 or ASTM E-308.

OptLab performs the color calculations according to the standards. The spectra must have been scanned on an absolute basis in the wavelength range of either 400 - 700 nm or 380 - 780 nm. Both %R and %T spectra can be used. The following result triplets are available in OptLab:

            Tristimulus values X, Y, Z
            Color coordinates x, y and tristimulus value Y
            Color coordinates x, y, z
            CIE color coordinates L*, a* and b* (additionally saturation C, hue h)

The following standardized illuminants are available:

            A            light of a light bulb
            C            daylight with cloudy sky
            D65        daylight with clear sky and high sun

The available observer angles of view are 2 degrees (focussed viewing, CIE 1931) and 10 degrees (broad-range viewing, CIE 1964).

The OptLab calculations are based on 4-column data sets, which comprises the necessary illuminants and observer data . The user may generate additional data files following the OptLab conventions to extend the scope of illuminants, wavelength ranges and observers. As well, the user may modify the result designations. color values typically are generated as a set of 3 values, but any single value can also be output. For each result value the number of decimal places can be defined.