A measure of the degree of contamination of one process color ink by another. For example, often a purportedly magenta ink will appear more distinctly red than a pure magenta (which is more of a purple-red) would, because of contamination by yellow pigments. Software (or other means) used to generate color separations need to take hue error into account, commonly accomplished by reducing the dot sizes of the unwanted shades. The hue error for a particular ink can be calculated by making three densitometer measurements—one with a red filter, one with a green filter, and one with a blue filter—and recording the high, middle, and low densities. Hue error can be calculated by using the formula
where H equals the highest density, M equals the middle density, and L equals the lowest density.