Complexity in Color Assessment
There are three things that are necessary to see color. You need an object, a light source for illumination, and an observer. This may seem like common sense, but have you ever thought of the variation that occurs in real-world settings between these influencers and how they impact our interpretation of color? There is complexity amongst these components, so let’s discuss objects, light sources, and observers individually.
The optical properties of objects are not constant because they depend on surface conditions. The same black colorant was used to produce the parts pictured below, but they visually appear much different based solely on their surface characteristics. Other things that can affect optical properties are:
- The thickness of the sample.
- The angle of incidence.
- The temperature of the object.
- The spectral composition of the light source being used.
Example of visual differences between objects.
Light sources can vary widely in their spectral power distribution. Changing the light source to view an object can affect its color dramatically. While people can visually evaluate color in many locations, such as offices, conference rooms, or the plant floor, it is recommended that visual color evaluation be performed in a calibrated light booth following ASTM D1729-96 which is the “Standard Practice for Visual Appraisal of Colors.” A light booth simulates various lighting conditions while providing consistency and accuracy in the viewing environment.
An observer can be a person or a color measuring-instrument, with neither being perfect. People are a natural tool for color evaluation. We can detect slight color differences largely ignore gloss and surface variances, and a trained observer is an excellent tool for evaluation. The cons of the human observer start with subjectivity. People interpret color differently. We can get optical fatigue, have color deficiencies, or even be color blind. A color instrument, on the other hand, is objective. It provides spectral curves and color difference numbers. An instrument aids trained color evaluators and is an effective tool for color matching and quality labs. The cons are that instruments do not measure transparent or translucent colors very well, don’t accurately measure highly saturated colors, and only Delta E numbers are sometimes used for approval instead of a trained person. Because both humans and instruments have strengths and weaknesses, they should be used in tandem to assess color differences properly.
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Color Technology Manager