Bidirectional Reflectance and Texture Database of Printed Special Effect Colors

A research project is underway to create a bidirectional reflectance and texture database of printed special effect colors. Such data is needed in the printing industry to determine the required measuring geometries characterizing the bidirectional reflectance distribution function (BRDF) and texture function (BTF), to develop quality measures for process control, and to simulate the prints’ appearance on displays (soft proofing). Flexo printing was used to apply 28 special effect inks with three tonal values on a matt and glossy paper substrate. The inks were selected to cover a wide range of different pigment classes and with respect to their demand in the printing market. To allow for multiple usage scenarios the inks were printed on a black and white background and partly finished with a glossy varnish resulting in a total of 672 different samples. The patches were measured in a preliminary stage with the BYK-mac multi-angle spectrophotometer. Evaluations on the diversity of the samples in terms of selected appearance parameters such as color flop or sparkle intensity are determined based on these measurements. The data is provided on our website and will be supplemented with additional measurements performed by a gonio-imaging system. Introduction In high-quality printing, e.g. in packaging, special effect inks are applied more frequently. The unique visual appearance, such as sparkle or geometry-induced color shifts, is caused by the optical properties of the comprised special effect pigments. Printing on top of particular background colors or applying gloss varnish might further boost these features. A major problem in the industry is the absence of a quality measure for process control if special effect inks are used. Desired effects are realized in a try-and-error manner that is time consuming and costly. Much research effort is needed to find the relevant appearance dimensions and to establish a visual distance measure for defining tolerances and to control the printing process. Furthermore, measuring geometries need to be determined that allow a sufficiently accurate estimation of the Bidirectional Reflectance Distribution Function (BRDF) or the Bidirectional Texture Function (BTF) of special effect prints. A database with BRDFs and BTFs of printed special effect prints covering a large number of pigment types and usage scenarios is required for this research. This paper describes an ongoing project of creating such a database including the selection of pigments and additional process steps for modifying the appearance of the final print. Bidirectional spectral and color data of the samples as well as texture parameters measured with a commercial multi-angle spectrophotometer are provided on our website. In addition to the needs in the printing industry, this database could be an interesting source for computer graphic rendering and complement existing databases such as MERL [1], CUReT [2] or the Artist Material BRDF Database [3].