Prediction of wood surface discoloration for applications in the field of architecture

Semitransparently coated wooden building elements such as facades and windows undergo discolouration during exposure to sunlight, depending on the environmental conditions and protective properties of the coatings. The present paper aims at the development of numerical prediction models of photo-induced discolouration as a basis for texture synthesis for CAD applications. Wood samples of European larch and Norway spruce were coated with several (semi-) transparent coatings with varying colours and dry film thicknesses and exposed to Xenon arc light with outdoor cut-off filter to simulate outdoor irradiation conditions. Colour prediction models were developed from the obtained colour measurement data in the CIE XYZ colour space, since the progression of corresponding values showed a monotonous curve characteristic of each coating system. A novel colour measurement procedure was developed to estimate the colour of early- and latewood in the annual rings of wood. This method made it possible to generate colour-consistent textures for use in rendering software, as demonstrated on two examples.