The measurement of sparkle

Sparkle is a non-uniform texture effect consisting of very bright spots distributed on a dark surround. To date the only commercially-available instrument able to quantify sparkle is BYK-mac. This instrument allows sparkle parameters to be obtained, which should correlate with the visual experience. However, the measurands corresponding to these parameters are not clearly defined and they cannot be measured by any other instruments. In this article, we describe a procedure to measure quantities of well-defined sparkle measurands. We present experimental results at a combination of well-distributed illumination/viewing geometries within the incident plane. From this study, four descriptors are derived which may be correlated with visual attributes of sparkle. Finally, the procedure to estimate the perceived sparkle at any given surround luminance from the measured sparkle quantities is explained.