Hue

In color theory, hue is one of the main properties of a color, defining its dominant wavelength. This characteristic determines whether we perceive a color as red, orange, yellow, green, blue, or violet. Understanding hue is essential for artists, designers, and anyone working with color.

Color Wheel

Defining Hue

  • Definition: Hue is the degree to which a color can be described as similar to or different from the primary colors red, yellow, and blue.
  • Representation: Quantitatively, hue can be represented by a single number, often corresponding to an angular position on a color wheel.

Colors with the same hue can vary in lightness and colorfulness, such as “light blue,” “pastel blue,” “vivid blue,” and “cobalt blue.” Brown, for example, is a dark orange.

Hue in Color Models

Hue plays a crucial role in various color models used in digital and print media.

  • RGB Model: In digital screens, the RGB model uses red, green, and blue to create different hues by varying their intensities.
  • CMYK Model: In print, the CMYK model uses cyan, magenta, yellow, and black to produce a full spectrum of hues.
  • Hex Codes: Web design uses hex codes, a six-digit combination representing RGB values, to specify hues.
Hue in the HSL:HSV encodings of RGB
Hue in the HSL:HSV encodings of RGB

Psychological and Cultural Significance of Hue

Hues have different psychological impacts and cultural meanings.

  • Red: Often associated with passion and excitement. In some cultures, it symbolizes luck and prosperity.
  • Blue: Conveys calmness and stability. Commonly used in corporate branding for its professional appeal.
  • Green: Represents nature and health. Frequently used in environmental and health-related contexts.
  • Yellow: Evokes happiness and energy. Also used to signify caution.

Deriving a Hue

The concept of a color system with hues dates back to 1830 with Philipp Otto Runge’s color sphere. The Munsell color system, developed in the 1930s, advanced this idea by creating a perceptually uniform color space.

  • Munsell Color System: This system organizes colors based on three properties: hue, value (lightness), and chroma (colorfulness).
  • Conventions: In most color spaces, the hue for red is set to 0°.
Albert Henry Munsell Color Model
Albert Henry Munsell Color Model

Hue in Opponent Color Spaces

In opponent color spaces, hue is computed along with chroma by converting coordinates from rectangular to polar form.

  • CIELAB and CIELUV: These color spaces use the angular component of the polar representation to determine hue.
  • Formulas: In CIELAB, hue is calculated using atan2(b*, a*), while in CIELUV, it uses atan2(v*, u*).

Defining Hue in Terms of RGB

Hue can also be derived from the RGB color model using a polar plot or color hexagon. The hue angle is calculated based on the positions of red, green, and blue in the color space.

HSV color space as a conical object
HSV color space as a conical object

Usage in Art

In painting, hue refers to a pure pigment without any tint (added white) or shade (added black). Manufacturers often label colors with “hue” to indicate safer or cheaper alternatives to toxic pigments while maintaining the original hue.

Hue vs. Dominant Wavelength

Dominant wavelength is a physical analog to the perceptual attribute of hue. It is determined by drawing a line from a white point through the color’s coordinates on a chromaticity diagram until it intersects the spectral locus. The intersection point identifies the color’s dominant wavelength.

Hue Difference Notation

Two main methods quantify hue difference. The first is the simple difference between two hue angles, denoted as Δhab in CIELAB and Δhuv in CIELUV. The second is the residual total color difference after accounting for lightness and chroma differences, symbolized as ΔHab* in CIELAB and ΔHuv* in CIELUV.

Names and Other Notations

There is some correspondence between hue values and color names. Traditional color terms are often used with more precise definitions. Alternative systematic notations include angle notations for color models like HSL/HSV, CIELUV, and CIECAM02. Alphanumeric systems like the Munsell color system, NCS, and Pantone Matching System are also common.

References

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