Color difference equations and the human eye


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Martin Habekost


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Ever since colors could be measured, various color difference equations have been used to describe the difference between two colors. The numbers generated from the various equations were not interchangeable and each number had a different meaning depending on which difference equation was used. The first internationally endorsed color difference equation was the CIE 1976 equation. This color difference equation deemed a difference or DE of 1.0 to be the smallest difference perceivable by the human eye. The DE76 formula was revised in 1994 and 2000 to adjust the numerical expression of difference to the way human observers perceive differences depending on the location of the color in color space and its intensity. An independent approach was done in 1984 by the CMC (Color Measurement Committee of the Society of Dyers and Colorists of Great Britain), which resulted in the DECMC formula. This formula also takes the various different color sensitivities of the human visual system into consideration. Now there are 4 color difference equations available. The fastest and easiest way to calculate color difference is the DE76 formula, but it has its drawbacks. Most widely used in the graphic arts field are probably the DE94 and/or DECMC formula. Although DE2000 has been available for some time now not much evidence was found to suggest widespread use in industry. Color standards and samples for this study were obtained through a color-managed press run. Overall 34 printed samples plus variations were printed. Volunteers were asked to rank the paired samples in the order of best match. All 17 volunteers had to undergo a color blindness test based on the Ishihara test charts. The obtained data was analyzed to correlate visual color difference with the various delta E equations mentioned above. Color management was used to create printed sample pairs that were equally distanced in color space. This study wanted to evaluate which of the four main color difference equations correlate best with human color vision using test subjects with little or no experience in viewing color differences. The main result of this study is, that the CIEDE 2000 and the DECMC formula relates quite well with the human perception of color differences in regards to Lightness, Chroma and Hue of the tested colors. If a recommendation has to be given in regards to which equation should be used in everyday application the formula DECMC would be favored, followed very closely by the formula CIEDE 2000.

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