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MacAdam’s ellipses

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MacAdam’s ellipses (In French ellipses de MacAdam) threshold ellipses that characterize the experimentally determined acceptances of just noticeable differences (JND, seuil de différenciation visuelle) around selected chromaticity coordinates in the CIE chromaticity chart CIExyY. These experiments were and are the basis for the creation of perceptually equidistant color systems like CIEUCS or CIELAB, in that these ellipses are transformed into equally large circles. This means that if the customer and the printing service provider can agree on tolerances, it can be assumed that one single Delta E tolerance value applies for the entire CIELAB color space.