News

An objects visual appearance can differ depending on the viewing angle. Modern effects require measurements not currently supported by standards

The visual aspect of a product can contribute drastically to sales. For this reason, different industrial sectors including automotive coatings, cosmetics and printed materials, are continuously looking to develop new attractive visual effects.

How an object looks doesn’t just depend on the colour but also on other attributes such as glossiness, iridescence, graininess, translucency, or ‘sparkle’ that can generate pinpricks of light in the body of a car. These attributes can change appearance depending on the angle of observation, or the direction or polarisation of the light falling on it, a phenomenon termed ‘goniochromatism’.
This goniochromatism can present considerable problems to manufacturers looking to produce visually striking products in a consistent and reliable way.

International standards designed to aid consistency in measurements on colour (ISO/CIE 11664) and gloss (ISO 2813) were not designed for visual effects that require a ‘bidirectional’ measurement approach – which requires the use of a Bidirectional Reflectance Distribution Function (BRDF) for which no standards exist.

The EMPIR project Bidirectional reflectance definitions (16NRM08, BiRD) has successfully addressed this problem and released a universal file format for BRDF definitions. This format has also been used in the EMPIR project SURFACE for measuring the lighting effect of road surfaces, gives a convenient method for arranging BRDF data to facilitate communication between measurement institutes, instrument manufacturers and industry making these types of measurements. These definitions detail not only the data required for measurements but also the metadata – to allow future reproducibility and machine-readability of measurements.

As well as the definitions the project also:

• developed and made available the open-source BRDF management software BiRDview for the quality control of surface appearance from different equipment.
• designed and built a new image-based detector for the measurement of gloss with an optical design based on ISO 2813 recommendation. The new instrument has advanced features that allow accessing the shape of the ‘specular’ peak and a materials visual properties like ‘orange peel’ or ‘contrast gloss’.
• performed a psychophysical experiment with the objective to quantify the effect of the type of illumination and of the surrounding on gloss perception was conducted.
• generated preliminary measurement scales for sparkle and graininess.

In addition, the project’s work led to the creation of a new International Commission on Illumination (CIE)  technical committee, TC2-85, dedicated to BRDF measurements which is expected to publish a document before the end of 2023.

Since the end of the project its website has been visited more than 74,000 times, indicating the great interest industry has in these forms of measurement.

The project was coordinated by Gael Obein (LNE-CNAM) , also the chair of TC2-85, who said about the new BRDF format:

“During the past years, each time I was receiving a BRDF measurement from a colleague, the first task was to write a short code to rearrange the data so that I can use them with my processing tool. The BRDF file format fixed this issue. We save time, and we are sure to avoid potential errors that could have occurred during the transcription”.

Work is continued in the SI broader scope project ‘New quantities for the measurement of appearance’ (18SIB03, BxDiff) that developed new metrological references for spectrophotometry to improve product quality control and virtual product representation in digital design.

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

Want to hear more about EURAMET?

Sign up for EURAMET newsletters and other information

Follow us on LinkedIn and Twitter