M-101 Basic Principles of Color Measurement
Color is measured in many ways, both visually and instrumentally. This tutorial is a primer on color and color measurement for designers, engineers, and technicians who need to understand basics of color and color measurement. Discussion will include how color arises, the tristimulus and opponent color methods that have evolved to quantify color, effects that change color, setting color tolerances, and devices used for visual and instrumental color measurement and evaluation. Thin film and non-thin film color measurement and considerations will be compared. At the end of the tutorial, you will have a working knowledge of the most commonly us ed color measurement systems, factors that affect color perception, and an understanding of color measuring instruments and geometries.
- Light sources and their effects
- Spectral reflectance/transmittance
- Observer effects
- Tristimulus color theory
- Color coordinate systems
- Color in thin film products
- Surface finish (specular versus diffuse) effects
- Instrumentation vs visual color evaluation
- Color control standards
- Color tolerancing methods
The tutorial fee includes the text, Billmeyer and Saltzman’s Principles of Color Technology, 3rd Edition, Roy S. Burns (John Wiley & Sons, 2000).Course Details:
This tutorial is designed for those who have little or no familiarity with color science, or who want to refresh their basic skills. Students should have mathematical skill at the level of high school algebra, and preferably have some experience in industrial color inspection methods. While color science is used for inspecting many products in industry, this tutorial is somewhat unique because it is geared toward thin films, a subject of some familiarity to the instructor.
A few simple demonstrations are used to assist in understanding, but the focus is on the understanding. These demonstrations will include effects of various light sources on color perception, and the effects of surrounding materials on perceived color.
Color perception requires the ability to distinguish between wavelengths of light across the visible spectrum. Color sensation requires a light source, an object to view, and a viewer or sensor. These three areas are introduced individually and their significance discussed. Along with this are the mathematical modeling analogs to these three: illuminants, spectral reflectance or transmittance and standard observers, respectively. From these analogs, we develop the Tristimulus values that lead to chromaticity coordinates in both the CIE1931 (x, y, Y) and CIE1976 (CIELAB, including LCH) systems. Both Tristimulus and opponent theories and their relationship are discussed. A simple calculation worksheet is provided to allow students to compute xyY and L*a*b* color coordinates from a given reflectance spectrum to give an appreciation of the inner workings of color measuring instruments.
There are other factors that affect perceived color. These include metameric shifts due to changes in light source, color changes in thin films with angle of view, and the effect of surface structure on perceived color. Brief mention is also made of color gamuts, especially in relation to the origins of color science, and shifts in perceived color.
Visual and instrumental color matching are commonly used in industrial inspection. Understanding color science can maximize the benefits of both tools, thereby improving color quality control. This is the motivation for understanding color theory. Therefore, we will discuss visual color matching methods as well as the most common form of instrumentation – the spectrophotometer based integrating sphere devices. This includes measurement geometries and methods, the role of integrating spheres, sample geometry, and potential problems in sample presentation. Specular included/excluded methods are explained and their usefulness is discussed with thin films in mind.
Finally, instrumental color measurement will rely on some form of color tolerance method to assess whether product color is acceptable. From the early days of MacAdam units to today’s more common ΔEcmc, and the more recent ΔE94, we explore the nature of human ability to distinguish colors. The shortcomings of simple color tolerances (±a*,±b*, for example) and the complexity of more appropriate methods are discussed and the formulae given.
Students should bring a calculator for the worksheet, and have a copy of the Text for their use during class and thereafter.Instructor: Greg Caskey, Grand Valley State University
started as an experimental nuclear physicist, then turned to thin film deposition and product development through various R&D efforts in mirror, electrochromic film, optical filter, and transparent conductive oxide coatings. At present, Greg is a Visiting Assistant Professor of Physics at Grand Valley State University. He has published over 25 papers in professional and technical journals and has several patents and one R&D 100 award.
This course is currently available via:
On Location Education Program