Contrast gloss evaluation by use of a camera-based gloss meter

Abstract

Visual gloss is a multidimensional perceptual attribute and its instrumental evaluation is considerably complex. Nevertheless, visual gloss plays an important role in the judgement of visual appearance of products. According to Hunter (1937), at least six perceptual attributes should be considered for a complete evaluation. Most of these attributes were initially determined with visual evaluations and subsequently with instruments using photodiode sensors that measure the amount of reflected light at multiple geometries to quantize aspects of gloss. However, partly due to the higher amount of information available to the human visual system compared to the gloss meter, there is only a weak correlation between human gloss perception and industrial gloss instruments. For this reason, these instruments are often combined with visual assessment for quality control e.g. at the end of production lines. Recently, the advancing technological developments in imaging hardware and software enabled the introduction of imaging sensors into gloss meters. This majorly increases the amount of captured information. In this study, a camera-based gloss meter design is adapted to include the measurement of contrast gloss and to study its influence on glossiness. Indeed, despite the considerable impact of contrast on gloss, as described by the contrast gloss formula developed by Leloup et al., this is not included yet in current gloss meters. The implementation of a contrast evaluation requires several additional sensor calibration procedures. Furthermore the difference in illumination levels, focus levels and viewing distance between instrumental evaluation conditions and realistic visual assessment conditions must be accounted for.