The color management industry uses many different systems to describe color mathematically, but there is no single accepted standard. There is also no way to convert from one color system to another. This means that the degree of color change measured by one system cannot be accurately compared to the degree of color change measured by another system.
Over the years specific systems have been defined to serve specific purposes. Manufacturers typically specialize in one type of system, depending on the primary purpose of their instruments and the needs of the industry in which they will be used. In commercial production, only measurements using the same color space yield consistent results.
In this article, we'll provide a high-level overview of color systems to help you work out the differences between them. If you're looking for a more in-depth look at color basics, we recommend downloading our eBook series "Principles of Color Management". You'll find detailed information on color spaces, systems and formulas in the fourth book.
A brief history of color spaces
A color space is a three-dimensional model that describes a set of colors that are mathematically related to each other. Colors are mapped along axes that represent different aspects of the color, such as hue or saturation. Aspects of the mapping depend on the type of color space.
CIE RGB, XYZ
Color management software typically uses color space variants defined by the International Commission on Illumination (CIE) in 1931. The "RGB" model aims to map all the colors visible to humans using the different wavelengths of red (R), green (G) and blue (B).
XYZ is a mathematical variant of RGB, also created in 1931, which extends the RGB space and avoids negative numbers. It uses three settings of primaries or tristimulus values.
laboratory
The CIELab space (or CIEL*A*B* or simply "Laboratory") was defined in 1976. The refinements of CIELab are intended to be perceptually consistent, meaning that their visual difference maps correspond to the colors space between.
CIELab represents colors according to the following three values:
L: Brightness, from black (0) to white (100)
a: the number of green (-) to red (+)
b: amount of blue (-) to yellow (+)
In this diagram, visible colors extend equally along both hue axes, so the chromaticity properties are relatively easy to see. As a theoretical model, CIELab includes "imaginary" colors beyond the range of human perception.
CIE2000
CIE2000 is a formula, not a color space. This calculation uses CIELab values, but brings the color difference closer to how the human eye actually perceives it.
A useful analogy: Suppose you need to drive to the store. The value of CIELab is like finding out the store is three miles away. At the same time, CIE2000 is similar to knowing that the store is three miles away, but this is also peak time and may take you longer than expected.
If we translate this to the color world, CIE2000 is our visual perception of color (often fooling us). For example, three cells off in a dark color are different from three cells off in a light color in terms of perception. CIE2000 will display information that CIELab cannot provide.
color difference
The amount of color variation acceptable in production work depends on business factors. To quantify this change, samples need to be measured and assigned a value. The measure of difference/distance between colors when using CIELab is ΔE (ΔE) or DE. Since CIE2000 uses CIELab but mathematically represents colors in a different way, numbers from CIELab DE and CIE2000 DE are not comparable. Usually, the CIE2000 DE number is smaller than CIELab.
Instrument Specifications
Since the DE numbers of CIELab and CIE2000 are not compatible, the product specifications of instruments using the two different systems should not be directly compared. Most instrument specifications use CIELab to allow customers to easily compare different products. However, some companies use CIE2000 DE numbers. Instruments using CIE2000 DE will be incorrectly favored or present false equivalence if listed together in a comparison table.
Below are the specifications for Datacolor Spectrophotometer s, including numbers for repeatability and inter-instrument agreement - all using CIELab:
DC 200
DC 500
DC 800
spectral vision
DC 20D
DC 45G
DC Check 3
In order to find the right Spectrophotometer for your needs, make sure that any specifications you are comparing use the same color system. Otherwise, you risk investing in a tool that doesn't work as expected in the field.
