GONIOPHOTOMETRIC COLOR MEASUREMENT FOR PAPERS

Abstract

The surface color of paper changes depending on observed angle. Such variations in surface color and their relationship to gloss are examined with the aid of a goniophotometer equipped with an interference filter. The results obtained are as follows:1) The smoother the surface and the more uniform the orientation of the constituent fibers of the sample, the closer the chromaticity coordinates get to the light-source color on the chromaticity diagram, when the sample is measured in a specular reflection direction.In other words, the larger the amount of specular reflection light in the goniophotometric reflection curve, the closer the chromaticity coordinates get to the light-source color on the chromaticity diagram.2) The larger the incidence-receiving angle, the larger the tristimulus values is, when the sample is measured in the direction of specular reflection. When the sample has a rugged surface, the angle which shows the maximum quantity of reflection light may deviate toward the direction larger in angle than the direction of the specular light. In this case, when the sample is measured by a goniophotometer at an angle showing the maximum quantity of reflection light, it shows the maximum tristimulus values.3) The goniophotometric color measured is shown by color mixture between the lightsource color and the object color on the chromaticity diagram.4) When the incidence-receiving angle of a paper is changed, its tristimulus values vary, resulting in color differences.5) When gloss is measured in the direction of specular relation, the angle showing the maximum quantity of reflected light may deviate toward a direction larger in angle than the direction of specular light. It is, therefore, recommended that the gonio-photometric reflection curve of the sample is measured before gloss is examined.