CIE standard observer

The CIE standard observer is a set of color-matching functions that model the average human visual response to wavelengths of light. It provides a standardized basis for specifying colors numerically.

Tristimulus values: Three numerical values representing a color through a specified set of color-matching functions. The observer’s functions integrate a spectrum into three such values.
CIE 1931 color space: A color space defined by the CIE in 1931 using three standard color-matching functions. The first standard observer was established for a small visual field in 1931.
Colorimetry: The measurement and specification of color using quantitative methods. The standard observer is a foundation of numerical color measurement.
Individual differences in color vision: Variations among people in color discrimination and visual sensitivity. A single standard observer cannot capture every person’s color-matching sensitivity.
Color-matching function: A function describing the amounts of primary lights needed to match monochromatic light at each wavelength. The standard observer consists of three such functions.
CIE 1964 color space: A colorimetric system based on the CIE’s 1964 standard observer for a 10-degree visual field. Later experiments supplied a separate standard for larger viewing fields.
CIE XYZ color space: A color space whose three primaries are mathematical constructs derived from color-matching data. Its tristimulus values use the standard observer’s functions.
Color vision deficiency: Reduced ability to distinguish some colors, commonly caused by differences in cone photopigments. Its color-matching responses can differ substantially from the standard observer.
Spectral power distribution: The distribution of radiant power emitted or reflected across wavelengths. It is the spectral input weighted by the observer’s color-matching functions.
CIE: The International Commission on Illumination, an organization that develops international standards for light and color. The commission adopted and maintains the standard observers.

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