Gloss, as has long been known, is a far more complex visual concept than the present methods of instrumental gloss evaluation are able to characterize. The instrumental analyses are either highly oversimplified (standard gloss meters) or oversimplified but with results still difficult to interpret (goniophotometry). The dimensionality and power of the directed reflectance information measured by existing tools is lower and less expressive than the information gained from a direct visual examination of a surface. In this article, a new measurement principle for gloss characterization is presented, aimed to give more comprehensive gloss information, which at the same time has an intuitive interpretation. The integrated optical system is compact and has illumination and receptor devices in fixed positions, which facilitates a mechanically simple realization. The instrument is a goniophotometer with a spatial resolution, but it is restricted to a constant angle between the illumination and the receptor. The measurement yields a "Reflectance Vector Map" (RVM) which is an approximate optical equivalent to the surface measured. The RVM simultaneously contains spatially resolved information about directed reflectance and surface apparent inclination. The resolution is high in both spatial and in angular coordinates. The measurement provides a complex massive data set, which when appropriately visualized is similar to the visual properties of the original surface and thus encourages further evaluation and interpretation. A homogeneity index called "Gloss Angle Smoothness" (GAS) is introduced, derived from the RVM, by weighing perceptually "positive" and "negative" components of gloss. The index correlates well with results obtained by a panel of experienced gloss judges asked to rate gloss homogeneity for the limited but demanding set of black printed paper surfaces tested. The GAS index performs considerably better than a panel of inexperienced judges.
Mikael Lindstrand, "An Angularly and Spatially Resolved Reflectometer for a Perceptually Adequate Characterization of Gloss" in Journal of Imaging Science and Technology, 2005, pp 71 - 84, https://doi.org/10.2352/J.ImagingSci.Technol.2005.49.1.art00010