John Seymour is an applied mathematician and color scientist. He is a professor at Clemson University, teaching color science and process control in the Graphic Communication school. He has worked as a consultant since 2012 under the name “John the Math Guy”. John currently holds thirty US patents, has authored over thirty technical papers, has presented at thirty conferences, and has keynoted at six conferences. He is an expert on the Committee for Graphic Arts Technologies Standards and ISO TC 130. He writes a blog which is described as “applied math and color science with a liberal sprinkling of goofy humor.”

Between 1992 and 2016, John was responsible for advanced product development for QuadTech, a manufacturer of process control equipment in the print industry. Prior to working with QuadTech, John worked as a scientific programmer in medical imaging, satellite imagery, electron microscopy, and spectroscopy. He holds bachelor’s degrees in mathematics and in computer science from the University of Wisconsin-Madison.

Six Things You Should Not Do With CIELAB

John Seymour, Clemson University & John the Math Guy, LLC

CIELAB has served us well. It has provided a reliable and unambiguous way for a brand owner to uniquely
specify a target color. It has enabled the use of spectrophotometers to assist through the workflow. ICC profiles and G7 are based on CIELAB. By using color difference formulas based on CIELAB, we have an objective way to determine if a printed product is in spec.

But, CIELAB is not without foibles. Its development occurred without a full knowledge of how it would be used. Some of the decisions that went into CIELAB have had far-reaching and underappreciated consequences. As a result, there are some expectations that we have for CIELAB that are questionable.

This paper describes a number of the problems with CIELAB by looking at applications that it shouldn’t be called on to do. There is a subtle undercurrent in the paper that the industry needs to to start considering how to replace CIELAB with a more moderns color space that does not have the issues that CIELAB has.

Things you should not do:

  1. Never call the a* axis red/green.
  2. Don’t’ assume that colors opposite one another are complementary colors.
  3. Don’t assume that two colors with the same CIELAB hue angle have the same perceptual hue.
  4. Don’t believe any ΔE color differences when the illuminant is significantly different from D50 or
    D65.
  5. Never, ever compute the color difference between two CIELAB values computed with different
    illuminants. Just don’t do it.
  6. Don’t assume that CIELAB is perceptually linear.