System for colour matching by computer

Colour is notoriously subjective: one person’s crimson is another’s carnelian. This is a particular issue for manufacturers who subcontract different suppliers to produce components that will eventually end up in a single product. The problem occurs in the car industry, where currently different suppliers exchange finished samples and employ trained colourists to match them visually.

A further challenge is presented by fashionable special-effect pigments that mixed into the paint to metallic or pearl lustre effects. These finishes vary under different lighting and from different viewing angles, and may even change colour completely – an effect known as ‘flip-flop’ – such as from copper red to green.

Now scientists at the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research have developed a means of characterising colour shades in the form of spectral data, which can be transmitted from computer to computer. “This enables us to measure even inhomogeneous multicolored structures with glitter and flip-flop effects,” explains researcher Volkmar Stenzel.

Each colour sample is registered from several different viewing angles. “We systematically tried out various combinations of viewing angle and illumination in a car manufacturer’s colour matching booth, and chose seven that clearly characterise each shade,” Stenzel continues.

The research was carried out in collaboration with the measuring device manufacturer ColorAIXperts.

At its destination the spectral data is converted back into colour images and compared with the manufacturer’s specification.

A test of 47 popular vehicle paint colors has shown the new system is suitable for use in the automotive industry. Experienced colorists compared four samples of each shade against a reference standard – using both colour samples in the conventional way, and spectral data on a computer screen. The different colour matching systems proved to be amazingly consistent with the colourists reaching the same decision in 82 percent of all cases.