The Joint Research Project „Bidirectional reflectance Definitions“ is a collaboration between National Metrology Institutes, partners from Industry and the research Community in Europe.
The aim of the project is to initiate standardisation work on BRDF measurements and thus to enable a reliable comparison of results provided by different measurement devices and better control of the visual effects of products.
JRP Number: 16NRM08
JRP Title: Bidirectional reflectance Definitions (BiRD)
JRP Timing: Start: 01/05/2017, End: 31/04/2020
Coordinating Organisation: Conservatoire national des arts et metiers (CNAM)
JRP-Coordinator: Gael OBEIN
Planned work and objectives
Standard parameters for measuring BRDF
The project will mobilise the best facilities available in Europe, to test and validate the influence of all pertinent measurement settings, e.g. settings of solid angles, illuminated and measured areas, and convergence of light beams, on the BRDF measurement. These tests will be performed on each category of special effect identified e.g. as quasi-lambertian, glossy, textured and goniochromatic effects. Guidance on BRDF measurement and how to sample the BRDF space will be made available to CIE TC2-85, as a first step to standardise BRDF measurements.
BRDF data handling and processing
In this project a universal BRDF data format will be developed following discussions, led by the partners by seeking input from, with a diverse community interested in acquisition, modelling and reproduction of material visual appearance, e.g. metrologists, spectrophotometer manufacturers, academics working on BRDF models, developers of virtual reality and video games applications, and end users from different industrial fields, as there are e.g. automotive, architecture, pulp and paper, and 3D printers. In addition, the most relevant appearance descriptors extracted from the raw BRDF data will be identified.
Gloss measurement and visual perception
A comprehensive collection of visual gloss scales will be gathered, and psychophysical studies will be performed as necessary to complement this collection of visual scales. The project will also gather and provide BRDF measurements of glossy samples. In addition, the project will propose to establish a CIE Technical Committee (TC) on gloss, with experts from CIE Division 1 and Division 2, together with industrial representatives.
Sparkle measurement and visual perception
Using a similar approach to that for gloss, the project will gather measurement data and visual scales for a large collection of sparkly samples and a CIE TC will be proposed with experts from different areas (metrology, vision and industry). Proposals for sparkle and graininess measurands will be developed following discussion, led by the partners, with manufacturers and end-users. Psychophysical experiments will be performed to test the correlation between the quantities proposed and the visual perception. Finally, a procedure which will enable the measurement of sparkle will be proposed to the new CIE TC for sparkle and graininess.
Impact on industry
The recommendations on the optical parameters for the measurement of BRDF will be crucial for instrument manufacturers to produce a new generation of spectrophotometers and to enable industrials to move from visual evaluation to objective BRDF measurement, leading to better control of the appearance of their products and less rejection by the customer. The consensual CIE standard observer for gloss, will also facilitate the development of a new generation of instruments which will allow a better control of gloss of materials with different nature or colour.
The uptake of adequate and trusted definitions of measurands and measurement procedures for sparkle and graininess that will be proposed in this project will enable the design and development of dedicated instruments. The uptake of the recommendations for the characterisation of the full BRDF of goniochromatic visual effect pigments will support the production of multi-angle spectrophotometers and promote the confidence of end-users that the best geometries can be used to characterise the product.
Impact on metrology
The normative work carried on in this project will support the development of a new generation of spectrophotometers that will increase the need of calibration and traceability.
Impact on relevant standards
This project will have a direct impact on different standardisation bodies working on new or improved standards, in particular CIE TC2-85, whose aim is to provide geometrical recommendations for the BRDF measurement according to the type of sample under investigation. The outputs of this project will be disseminated to this committee through a technical recommendation and presentations. Other standardisation bodies e.g. ISO TC35/SC14, ISO/TC 6 and CIPM – CCPR will also be briefed at committee meetings. Another step towards the incorporation of the outputs of this project on standardisation is the creation of new CIE technical committees on gloss and sparkle, which will be provided with working drafts on i) instrumental and visual evaluation of gloss, and on ii) the most appropriate definitions of sparkle and graininess measurands and procedures for their measurement, respectively.