ARCHIVED - Reflecting on colour
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April 06, 2009— Ottawa, Ontario
There's more to colour than meets the eye, according to NRC specialists who have taken the science of measuring colour and appearance to new levels of precision.
The NRC Institute for National Measurement Standards (NRC-INMS) has developed a leading-edge "gonioreflectometer" — a highly sensitive instrument that can rapidly measure, in three dimensions, the reflectance properties of materials with a variety of colour attributes and surface properties. That's good news for manufacturers of new iridescent paints that reflect a range of hues and exhibit different surface texture or other spatial effects, when light hits them from different angles.
Cosmetics, cars, appliances, clothing and high-end packaging are some of the products for which the proper management of colour and appearance are critical for commercial success. NRC's capacity to accurately measure 3D reflectance will also serve other interests, such as anti-counterfeiting, remote sensing, cultural heritage and medical imaging applications, or the production of new geometry-sensitive materials, such as special effect pigments.
Dr. Réjean Baribeau, a researcher at NRC-INMS, is the mind behind the enhanced gonioreflectometer. "With integrated robotics to move the target material around, our design allows us to measure bidirectional reflectance at higher speed and less cost than other existing similar instruments," he explains. "Our gonioreflectometer is also smaller and easier to use."
A gonioreflectometer consists of a light source illuminating the material to be measured and a sensor that captures the light reflected from that material as it rotates around a hemisphere. The rotation of the light source and the sensor around the target material is what allows for reflectance to be measured in 3D.
"It's extremely challenging to quantify absolutely the surface appearance of materials, or to predict the degree to which different materials will match," says Dr. Baribeau. "Measurements must take into account the interplay between visual perception, the angle and quality of lighting, as well as the optical properties and surface texture of a material." He demonstrates this by holding up a manufacturer's paint sample that reflects a dramatically different colour of varying intensity when held at different angles. Like a peacock's tail flashing in the sun, the colour of the paint chip changes from purple to teal blue, and then to green.
"Our instrument allows us to capture the full reflectance spectrum simultaneously instead of creating a multitude of separate measurements based on different wavelengths," says Dr. Baribeau. "We can characterize the 3D optical qualities of materials much faster."
NRC's objective is to open a new national measurement facility that will allow industry to measure materials with unusual optical qualities and calibrate their own 3D reflectance measurement instruments. The national metrology institutes of other nations will also benefit from NRC's enhancements.
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National Research Council of Canada
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