CIELab is the color space model used to measure the lightness, hue and chromacity of any given color. It is the most popular color model used among offset printers today and is considered the industry standard. It’s values are used to control and manage color reproduction on a printing press.
What does CIELAB stand for?
The first part of the acronym CIE stands for the International Commission on Illumination. It’s actually originally in french and is written as Commission Internationale de L'éclairage.
The second part of the acronym LAB stands for the values withing the CIELAB color model. The letter “L” stands for lightness. The letters “A” and “B” represent the position that is plotted on the color space model. Notice the position of the lightness (+L on top) and the "a" and "b" coordinates in the model below.
History of CIELAB
The International Commission on Illumination is considered the international authority on color, light and illumination. The organization was originally established in 1913 but it did not publish this color model until 1976. Hence you will often see the acronym CIELAB 1976.
How do offset printers measure LAB values?
Offset printers will use an instrument called a spectrophotometer. It is a hand held device and can be used right at the printing press for the sake of color evaluation and correction within the CIELAB color model.
In the picture above, the spectrophotometer (on the table upper left) is used to read colors within the CIELAB color space. These values are fed back to a computer that will display it’s LAB values as well as ink density. When there is a difference between the desired color and the actual color coming off the printing press, this is called a delta E. The pressman may need to make adjustments on the press or change his materials.
Monitoring Variations in the CIELAB Color Space
Offset printers need to take regular measurements to determine any variations, or Delta E, to match a standard provided by the customer.
The customer will define a tolerance in what is allowable, but this is usually established by what are referred to as ISO standards. However a customer may be much more picky when it comes to logos or colors that affect branding.
As mentioned, when comparing two color values we get what's referred to as a Delta e. This is calculated by means of a mathematical formula. A difference of 1.0 is understood to mean the smallest color difference that can be seen by a human eye. However since this measurement was established in 1976 it has been determined that some can see differences in color less than 1.0. This human factor emphasizes the need for having instruments to measure a color, as no two sets of eyes see color the same.
Why do we have the CIELAB color model?
This brings us to the reason why there is a CIELAB color model. All humans see color differently. By having a standard measurement tool, color uniformity can be maintained not just in a single offset printing press during a single press run. Multiple offset printers can be used in perhaps multiple countries. Two printers using different raw materials on different printing presses even in different countries can print two products that are virtually the same if a single strict color measurement standard is used and abided by, such as CIELAB.
Summary
CIELAB 1976 has been used as an industry standard in offset printing for many years. It allows printers to measure color effectively. Different models have been introduced such as CIE94 and CIE2000, however they similarly represent a similar result that all offset printers are trying to achieve: a uniform way of measuring color and not relying on the imperfect and often varied perception of color.
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