Optics: measuring and testing – Document pattern analysis or verification
Patent
1998-10-26
2000-11-14
Kim, Robert H.
Optics: measuring and testing
Document pattern analysis or verification
356445, G06K 974
Patent
active
061477508
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and to apparatus which will provide a basis on which the gloss quality of a sample surface on a sample, such as a paper sheet, can be determined by illuminating the sample surface and registering the intensity of the light reflected therefrom.
BACKGROUND OF THE INVENTION
The gloss of, e.g., paper products such as LWC-paper has been measured with a large number of different methods over a long period of time. The majority of these methods, and primarily the normative methods, are concentrated on mean gloss levels over a large surface area. Since the mean gloss level is not the only parameter contributing to the subjective impression of gloss quality, there is a need of an evaluation method that conforms better to the human evaluation of gloss quality, which includes the perception of gloss variation.
When studying the phenomena of gloss, particularly of printed paper, it has been found that the main caracteristics of the gloss variation can be described if the surface of the paper is approximated by a model surface comprising small flat surface elements, gloss facets, wherein gloss variation is determined on the basis of the orientation of the individual facets with respect to the plane of the paper and the reflected intensity of the individual facets. However, no method and apparatus that can be used in practice have been proposed for determining gloss variations based on this gloss facet approximation.
One object of the present invention is to provide a method and apparatus of the aforesaid kind which can be used effectively to carry out a multiple of different types of gloss variation evaluations on a sample surface in accordance with the principles of the aforesaid gloss facet approximation.
The object is achieved with the features set forth in the following claims.
SUMMARY OF THE INVENTION
According to one aspect of the invention, the sample surface is exposed in an image registering area by controlled rotary movement of the sample surface through the image registering area, or by controlled rotary movement of this image registering area over the sample surface, wherein the intensity of light reflected from a plurality of spatially well defined part-surfaces of the sample surface is registered several times during such rotary movement while, at the same time, determining the position, and in turn the viewing angle of respective part-surfaces in the image registering area so as to establish, what we here define as an image volume representative of registered light intensity as a function of the position of said part-surfaces within the sample surface and of the viewing angle.
Because registration is effected during said rotary movement, e.g. rotary movement of the sample surface through the image registering area, it is possible to obtain a well adapted variation of the viewing angle; in other words light reflected from the sample surface can be registered from a sufficiently large variation of angles of incidents. Compilation of an image volume of the registered light intensities enables different types of gloss quality evaluations of the sample surface to be carried out effectively during the registration process, or separately on the basis of the stored image volume.
When the sample surface is brought to a specific convex-curve shape prior to exposure in the image registering area, there is obtained an appropriately large spread of the viewing angle in conjunction with said rotary movement, as compared with a flat sample surface.
When the sample surface is given a circular-cylindrical shape and exposed in the registering area by rotating the cylinder about its centre axis, the sample can be mounted on the end of a simple mechanically rotatable shaft, drum or the like, so that each part-surface can be moved through the image registering area in a readily controlled manner.
Other features of the invention and advantages afforded thereby will be evident from the following claims and also from the following description.
The invention
Johansson Per-.ANG.ke
Lindstrand Mikael
Kim Robert H.
Lezdey John
Merlino Amanda
STFI
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