Color Difference Equations and the Human Eye

by Martin Habekost, Ryerson University

Discussion on the color difference equations. DEcmc introduced the weighting factors and was developed for the textile industry. It is used widely for color matching in the ink manufacturing industry.

Second revision was on 1994, again with weighting factors that are adjustable as well. It is even more realistic than cmc, but it has weaknesses in the blue and violet region.

So CIE made DE2000, which is considered to be the best and is recommended. It is not used in the industry though. What I have heard is that it moves the color space around and it creates a moving color target.

Martin suggests after the experiment that DE2000 or DEcmc are to be used, and preferably DEcmc because the data were more coherent.

Q&A
Important considerations were raised during the Q&A section. First, Dave McDowell focused on the need to establish the weighting factors that are more fitting for our processes. After all, the developers of these equations reccomend each user to develop the factors that suit their processes best. Why don't we do so? One might say: lack of awareness or knowledge, or time to test out what is more fitting. I've seen people using a DEcmc(2:2) as QC. You cannot imagine what comes through as OK with these factors. I have seen some others using factors that narrow down the variation of hue, but allow variation in chroma and lightness. This should be very useful for the ink making process, where hue is the most critical parameter. However, the variations during the printing process would be on IFT, and if C* (being sensitive to IFT variations) has a wide tolerance, it is likely to be very forgiving... more than what a customer can forgive.