Page 48 - Handbook of Surface Improvement and Modification

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Gloss Enhancement

3.1 GLOSS PERCEPTION

The shine or luster on a smooth surface is a common definition of gloss. It appears very
simple to grasp but very difficult to evaluate as the following information shows.
Humans are remarkably good at making fast and accurate judgments regarding mate-
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rial properties. The brain uses a variety of visual signals to estimate gloss. The glossiness
is specified only by small image areas containing highlights and a slight change in an
object (e.g., a minor change of material or smoothness) can cause huge differences in the
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perceptual impression of gloss.
The functional magnetic resonance imaging measurements of human brain reactions
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were used to localize brain areas which preferentially respond to glossy objects. Two
brain areas (pFs and V3B/KO) appear to be important in processing information about
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gloss. Figure 3.1 shows the results using either pFs (Figure 3.1A) or V3B/KO (Figure
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3.1B) as the reference region, respectively. Blue areas indicate brain areas that are signif-
icantly influenced by the reference region, while the green color map identifies locations
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that have a significant influence on the reference region. It was found that activity in pFs
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had a strong influence on both dorsal and ventral areas. This may reveal that gloss-related
activity is used for the processes of object processing (in ventral cortex) in addition to
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affecting depth estimates (estimated in dorsal areas). By contrast, the estimated connec-
tivity in V3B/KO was quite different. V3B/KO mainly received information from ventral
areas rather than having an influence on them, perhaps indicating that gloss information in
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V3B/KO is inherited from a primary locus in ventral areas. These findings point to a dif-
ferent role of V3B/KO and pFs, suggesting that V3B/KO may be tuned to processing
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highlight boundaries or 3D shape properties rather than to glossiness processing.
In summary of the above, it is relatively easy to get a good response from trained
individuals regarding perceived glossiness but still quite difficult to understand processes
which lead to these estimations. In addition, human evaluation of glossiness lacks preci-
sion because it can only be expressed in a form of rating scale of relatively low accuracy.
This does not include bias which is related to the subjectivity of human evaluation. For
this reason, it is essential to develop a precise method of measurement which can elimi-
nate, bias, lack of precision, and repeatability.
Ingersoll was one of the first to conduct studies on gloss of paper using a glarimeter.
He assumed that the gloss was the amount of specular reflectance of light compared to the
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amount of diffusely reflected light. The instrument calculated this proportion using a
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polarizing filter. The instrument was used to determine the quality of a paper produced by
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paper mills. Almost twenty years later, Hunter proposed a number of different aspects of