Reflectance of three paper grades was investigated using a pressure gauge, an imaging system, and a spectrophotometer. It was observed that under high pressure, dark-colored areas appear in paper when using the imaging system. The area of the dark pattern increases as the pressure is raised. Reflectance measurements as a function of wavelength confirmed that the dark patterns appear due to the contact of the paper and the probe window of the pressure gauge. Based on results by other researchers the amount and the nature of optical contact observed depends on structural properties of paper such as surface roughness, formation, and compressibility. Although there are differences in the spectral properties of different paper grades they all share the common feature that the reflectance is decreasing as a function of the applied pressure. An empiric result for the fine and the super-calendered (SC) paper samples measured is that they both have an exponential dependence of total reflectance as a function of applied pressure when the illumination wavelength is kept constant.
In this paper, we extend the data analysis of gloss from prints making use of the visibility concept for the signal of a diffractive optical element based glossmeter. It is shown that the visibility is sensitive to the borders of the prints on uncoated paper. We suggest that the gloss map is due to the simultaneous dependence on both the refractive index and the surface roughness of the print, whereas the visibility is independent of the refractive index, and hence is sensitive only to the surface roughness. The visibility map and relevant statistical parameters provide new means to inspect prints on paper and other substances.
We introduce a sensor for providing information on the local contrast gloss (or luster) of products. The sensor also provides information of the local specular gloss of the object. The signals of this sensor are produced by diffractive optical elements from fields that are scattered in the diffuse and specular directions from the object. We present specular gloss, diffuse-reflectance factor related to the contrast gloss, and visibility maps measured from black prints on paper. High variation can be observed in the relevant gloss parameters obtained from the printed area. In addition, borders of the print can be clearly detected from the diffuse-reflectance-factor maps. The sensor also allows detection of raster points of a print. This sensor opens up entirely new means to study prints and other substances.
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