In the standard “DIN 6167 Definition of yellowing of nearly white or nearly colorless materials” developed by the Volkswagen automobile company, a procedure for determining the level of yellowing of white or nearly colorless materials is described.
For nearly white or nearly colorless samples, a one-dimensional number is calculated from the spectral data, called the yellowness index. This index quantifies how far a sample's color deviates from ideal white. The larger the value, the more yellow the sample appears. Often such samples do not appear simply yellow, but show a significant difference in hue and brightness. Therefore, they need a three-dimensional color description: red/green, yellow/blue, and light/dark.
This application provides numbers associated with visual ratings of the yellowness or whiteness of white and nearly white or colorless object color samples when viewed in daylight by an observer with normal color vision. White textiles, paints, and plastics are a few of the materials that can be identified by the yellowness or whiteness indices calculated with this application.
For a complete analysis of object colors by a given observer and under a given illuminant, three parameters must be used. However, for nearly white samples it is often useful to calculate single-numbered yellowness or whiteness scales. This exercise provides suggested equations for such scales and discusses their derivation and use, as well as the limits of their applicability.
For the purposes of this standard, the following terms and definitions apply:
This practice is only used to compare samples of the same material and the same general appearance. For example, a set of samples to be compared should generally have similar gloss, texture, and thickness (if not opaque), and translucency.
The combination of measurement and calculation that results in yellowness or whiteness indices is a psychophysical process, meaning that the procedures specified are designed to provide numbers that correlate with visual estimates made under typical observation conditions. Since visual observation conditions can vary widely, users should compare calculated indices with visual estimates to ensure applicability. Other standards exist that address visual estimation of color and color difference (e.g., ASTM E313-20, ASTM D1535-01, ASTM D1729-16, ASTM E1360-05, ASTM E1541-98, and ASTM E1499-16.
In short, the whiteness index is used to measure any material that is close to white. In contrast, the yellowness index is used to determine how far a sample's color deviates from ideal white.
Among the numerous testing, measurement, analysis and evaluation studies that our organization has carried out for businesses in various sectors, our organization also provides testing services defined in the standard “DIN 6167 Definition of yellowing of almost white or almost colorless materials” with its trained and expert staff and advanced technological equipment.
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