Method and apparatus for measuring optical properties layer of flexible substrates

The invention relates to a method and an apparatus for measuring optical properties of flexible substrates with at least one roller, wherein the substrate is in contact with at least a roll surface and at least one measuring device and an evaluation device with which the reflection and transmission is measured. The object of the invention is to remedy the difficult analysis of measured signals to highly reflective rollers. The object is apparatus and method mutually solved in that a rolling surface comprises a first segment having a first reflectance value and a second segment having a second reflectance value on its periphery, wherein the first segment and the second segment are arranged on the circumference of the roll surface side by side alternately , It is determined, a first reflectance value in a first segment of the roll surface and a second reflection value in a second segment of the roller surface, wherein the first and the second segment of the roll surface have different reflection values.