Color stimulus
A color stimulus is visible electromagnetic radiation that enters the eye and by direct stimulation of the retina a color perception causes.
In contrast, color of the sensation of an observer, not a physical property of light. Light that does not fall into an eye is only radiation . Light that falls into a color-capable eye becomes a color stimulus and can be perceived as color by the observer.
Color stimulus and color valence
What color a human observer perceives depends on the interaction of the spectral composition of the light with the three types of color-sensitive sensory cells ( cones ) in the retina. For the neural signals of three types of cones, the color valences , there are significantly fewer possible combinations than for the infinite number of spectral colors of light. Therefore, the human eye cannot distinguish all possible combinations of spectral colors.
This does not mean the fact that some spectral distributions are too similar to be differentiated by the eye, but there are whole classes of different spectral distributions (i.e. different color stimuli) that produce the same color sensations in humans. Each class of color stimuli that appear the same is described by a parameter that is clearly assigned to it, the color valence . Two color stimuli trigger the same color sensation if they have the same color valence. It can be described by three numerical values and contains only that information about the color stimulus that is decisive for the color sensation triggered, and thus considerably less information than the full spectral distribution. The colorimetry investigated the properties of color stimuli, their relationships and the rules for calculating their mixture.
Color stimulus and color sensation
The detection of color stimuli by the color receptors of the eye, the pre-processing of these stimuli in the nerve cells of the retina , their coding and transmission in the optic nerve as well as their processing in the visual cortex of the brain are complex psychophysical procedures that at the end of color perception is. Color perception with its dependence on the observation conditions as well as its contrast and after-effects is subject to much more complex laws than colorimetry. There is no simple one-to-one relationship between the color valence of a color stimulus and the color sensation triggered. Color appearance models try to capture these relationships.
Color stimulus function
The color stimulus can emanate from a primary light source as well as from the surface or the depth of an illuminated body .
The spectral distribution of a color stimulus is called the color stimulus function φ (λ). In the case of a self-radiator, this function is equal to its spectral distribution S (λ). In the case of a secondary light source , i.e. a body color , the color stimulus function is the product of the radiance factor β (λ) and the spectral distribution of the light source.
Body colors change the spectral composition of incident light according to their transmission and remission behavior. For practical reasons, a distinction is made between transparent colors (colored solutions, color filters) and reflective colors (paint, textile coloring). With see-through colors, the body influences the color stimulus in the volume, indicated by the spectral transmittance τ λ . In the case of top-view colors, the color stimulus is influenced by the surface, described by the spectral reflectance β λ .
| term | Site of action | Type of action | Area of Expertise |
|---|---|---|---|
| Color stimulus | Light source | electromagnetic radiation | Development of colors / optics |
| Color valence | Eye ( cone ) | Spectral-specific response of the retina | physiology |
| Color sensation | brain | Color perception | Physiology / Psychology |
literature
- Manfred Richter: Introduction to colorimetry . Walter de Gruyter, Berlin 1981
Individual evidence
- ↑ a b DIN 5033-1 . In: German Institute for Standardization e. V. (Ed.): Colorants 1 . 7th edition. DIN-Taschenbuch 49.Berlin, Vienna, Zurich 2012, ISBN 978-3-410-23202-5 , pp. 4 .
- ↑ International Electrotechnical Commission (IEC): International Electrotechnical Vocabulary , ref. 845-03-02, color stimulus : Color stimulus : Visible radiation that enters the eye and causes a colorful or achromatic color sensation. ("Color stimulus: visible radiation entering the eye and producing a sensation of color, either chromatic or achromatic"), accessed on October 28, 2015.
- ↑ G. Wyszecki, WS Stiles: Color Science - Concepts and Methods, Quantitative Data and Formulas. 2nd ed., John Wiley & Sons 1982, ISBN 0-471-02106-7 (Wiley Classics Library Edition, 2000: ISBN 0-471-39918-3 ), p. 723: A color stimulus is radiation of a given strength and spectral composition, which enters the eye and causes a color sensation. ("A color stimulus is radiant power of given magnitude and spectral composition, entering the eye and producing a sensation of color.")
- ↑ M. Richter: Introduction to colorimetry. 2nd edition, Walter de Gruyter, Berlin / New York 1981, ISBN 3-11-008209-8 , p. 13