16NRM08 BiRD: Bidirectional reflectance definitions

• Forschungsstelle: METAS
• Projektnummer: F-5116.30090

Schlüsselwörter (Englisch)

Goniospectrophotometry, Gloss, Goniochromatism, Iridescence, BRDF, Colour, Appearance. Sparkle, Material

Kurzbeschreibung (Englisch)

The commercial success of a product is often dependent on its aesthetic appearance. For this reason, different industrial sectors e.g. automotive coatings, cosmetics, printed materials, are continuously looking to develop new attractive visual effects. This project focuses on the pre-normative work required to clarify how bidirectional reflectance measurements on standard materials and surfaces exhibiting goniochromatism, gloss and sparkle visual effects should be carried out. In this field, the relevant radiometric quantity is the Bidirectional Reflectance Distribution Function (BRDF), which contains extensive information about the light reflected by a surface and therefore information on the appearance of a product. Guidance will be developed on measurements of BRDF, BRDF sampling strategy and arrangements for BRDF data sampling, processing and visualisation according to the visual effect, e.g., goniochromatism, gloss and sparkle. This will enable a reliable comparison of results provided by different measurement devices and better control of the visual effects of products.

Objects are identified through their shape, size and “visual attributes” i.e. colour, gloss, transparency and texture. These attributes define the appearance of the objects. For industrial manufacturers, the appearance of a product is important at the quality control level (because the visual appearance informs the manufacturer on the constancy and reproducibility of its production) and at the commercial level (because the appearance of a product directly influences the customer and the purchase decision). Within the last 20 years, substantial effort has been undertaken by industrial manufacturers to create attractive and sophisticated visual effects. However, current standards on colour measurement (ISO 11664) and gloss measurement (ISO 2813) are not adapted to the characterisation of sophisticated visual effects and no standard exists for BRDF or sparkle. CIE (Commission Internationale de l´Éclairage) has currently initiated work on this through TC2-85. Following on from the need to characterise visual effects and the absence of standardisation and standard methods in this field, manufacturers of spectrophotometer systems and NMIs are developing their own instruments, using different optical parameters and methods of measurement. This leads to lack of comparability of BRDF, gloss and visual structure for certain objects.

This is a joint research project carried out in the framework of the European Metrology Programme for Innovation and Research (EMPIR) (see:http://www.euramet.org/research-innovation/empir/). The EMPIR initiative is co-funded by the European Unions's Horizon 2020 research and innovation programme and the participating states. METAS is one of the project partners in the Projec

Projektziele (Englisch)

The scientific and technical objectives of this project are to:

1. Propose standard parameters for the measurement of the BRDF of particular materials and optical surfaces in the visible range in order to improve the traceability to the SI between users and NMIs, and therefore to allow for better agreement between commercial goniospectrophotometers. The focus will be on i) settings of solid angles, ii) illuminated and measured areas, and iii) convergence of light beams. In addition, to provide guidance on how to sample the BRDF space efficiently and to propose a minimum number of measurement geometries according to the appearance properties of the specimen.
2. Propose arrangements for data handling and processing for BRDF measurements when a large amount of data is obtained.
3. Propose a new method for gloss measurement that correlates with visual perception. The contribution will be based on i) reflectance measurements, ii) visual evaluations and iii) definition of a standard gloss observer.
4. Propose a consensual definition of sparkle and graininess measurands and to define procedures for their measurement in correlation with visual scales for sparkle and graininess.
5. Facilitate the uptake of the technology and guidance developed in the project by the measurement supply chain e.g. instrument manufacturers and end-users e.g. automotive, cosmetics, pigments, packaging and 3D printing industries. In addition, to contribute to the standards development work of international standardisation bodies e.g. CIE. Dissemination of project results will take place as early as possible to establish a standardised approach.