Colorms

Colorms is a term used in some discussions of color theory to denote a scalar value intended to reflect the overall magnitude or intensity of a color, incorporating both lightness and chroma. It is not an officially defined or standardized metric within color science, and its use varies across sources.

In practice, colorms are defined differently by different authors, and there is no universal formula. A common illustrative approach treats a colorm as a function of a color’s values in a perceptual color space, such as CIE L*a*b*. One illustrative formulation is colorm = sqrt((L*/100)^2 + C*^2), where L* is lightness and C* is chroma derived from a* and b*. It is important to note that this is a conceptual example rather than a standardized method; other weightings or normalizations may be proposed.

Colorms differ from established color-difference or color-magnitude metrics. They are not intended to quantify perceptual distance between colors in the way Delta E or CIEDE2000 do. Instead, colorms are typically used as teaching aids or visualization tools to discuss how varying lightness and chroma influence the perceived strength of a color, rather than as a precise measurement for color matching.

Variants of the concept exist, including different normalizations, the inclusion of hue components, or alternative mathematical norms. Because there is no consensus, sources that employ colorms usually specify their exact definition and calculation method to avoid ambiguity.

See also: color theory, CIELAB, chroma, luminance, color difference metrics.