The color management industry uses a number of different systems to mathematically describe colors, but there isn’t one single accepted standard. There’s also no way to convert one color system to another. That means the degree of color variation measured with one system can’t be accurately compared with measurements from another.
Specific systems have been defined over the years to meet particular purposes. Manufacturers often focus on one type of system, depending upon the primary purpose of their instruments and the needs of the industries that use them. In commercial production, only measurements using the same color space can generate consistent results.
In this article, we’ll provide a high-level overview of color systems to help you navigate their differences. If you’re looking for a more in-depth explanation of color fundamentals, we recommend downloading our ebook series, Principles of Color Management. You’ll find detailed information on color spaces, systems and formulas in book four.
Brief history of color spaces
A color space is a three-dimensional model that describes a set of colors mathematically in relationship to each other. Colors are mapped along axes that represent different aspects of color such as hue, or saturation. The mapped aspects vary depending upon the type of color space.
CIE RGB, XYZ
Color management software typically uses variants of the color space defined in 1931 by the Commission International de ľéclairage (CIE). The “RGB” model was intended to map all colors visible to humans using different wavelengths of red (R), green (G), and blue (B) light.
XYZ is a mathematical variant of RGB, also created in 1931, that expands the RGB space and avoids negative numbers. It uses three set primaries or tristimulus values.
The CIELab space (or CIEL*a*b* or simply “Lab”) is a refinement defined in 1976. CIELab is intended to be perceptually uniform, meaning that the space between mapped colors corresponds to their visual differences.
CIELab expresses colors according to three values:
- L: Lightness, from black (0) to white (100)
- a: Amount of green (-) to red (+)
- b: Amount of blue (-) to yellow (+)
In the diagram, visible colors extend equally along the two hue axes, making chromatic properties relatively easy to see. As a theoretical model, CIELab includes “imaginary” colors that are outside the range of human perception.
CIE2000 is a formula, not a color space. It’s a calculation that uses CIELab values but brings color differences closer to what the human eye actually perceives.
A helpful analogy: Let’s say you need to drive to the store. A CIELab value is like finding out the store is three miles away. Meanwhile, CIE2000 is similar to knowing that the store is three miles away, but it’s also rush hour and might take you longer than anticipated.
If we translate that to the world of color, CIE2000 accounts for our visual perception of color (which can often deceive us). For example, being three units off with a dark color is different from being three units off with a light color when it comes to perception. CIE2000 will reveal that information where CIELab cannot.
The amount of color variation considered acceptable in production work depends upon business factors. To quantify that variation, samples must be measured and assigned numeric values. The difference/distance metric between colors when using CIELab is ΔE (Delta E), or DE. Since CIE2000 uses CIELab but expresses colors differently mathematically, the CIELab DE and CIE2000 DE figures aren’t comparable. In general, CIE2000 DE numbers are smaller than those for CIELab.
Since the DE numbers for CIELab and CIE2000 aren’t compatible, product specifications for instruments using the two different systems shouldn’t be directly compared. Most instrument specs use CIELab in order for customers to easily compare different products. Some companies, however, use CIE2000 DE figures. If listed together in comparison charts, the instruments using CIE2000 DE will be inaccurately favored or appear falsely equivalent.
Following are the specifications for Datacolor instruments, including figures for repeatability and inter-instrument agreement – all using CIELab:
To find the best spectrophotometer for your needs, be sure any specs you’re comparing use the same color system. Otherwise, you may invest in instruments that don’t perform as expected in the field.
Our Datacolor team can help you better understand different color spaces. And we can show you a solution with the repeatability and inter-instrument agreement levels you’re looking for.