Optimal color
An optimal color is an idealized body color with a rectangular spectrum.
history
The optimal color goes back to a suggestion by Wilhelm Ostwald . At the beginning of the 20th century, the search for a computationally controllable system for colors arose due to demands from industry and the possibilities of measuring spectra. In 1919, physicist Erwin Schrödinger was able to prove in his work Theory of Pigments of Greatest Luminosity that optimal colors are the theoretical limit of all realizable body colors.
construction
The idealization of an optimal color consists in that a maximum of two jump points are allowed for its spectrum . Otherwise the intensity, the degree of remission β, only has the value 0 or 1.
If the spectrum has only one jump point, a distinction is made depending on its location (description in each case in the direction of increasing wavelengths ):
- Short-end colors; blue colors that start with β = 1 at low wavelengths (at the "short end of the spectrum") and then decrease to β = 0 at a defined wavelength
- Long-end colors; red colors in which the reflectance jumps to 1 and maintains this value until the (“long”) end of the visible spectral range.
If the spectrum has two jump points, it is:
- green middle colors whose full area (β = 1) lies in the middle.
- Means fail colors, if the curve in the middle of the value β has = 0; in principle they belong to the group of violet ( purple ) tones.
properties
An optimum color is of all colors the same color type , the largest brightness and the same for all color hue and the same brightness, the highest saturation .
David L. MacAdam and Siegfried Rösch later expanded the concept in order to be able to make statements about the totality of theoretically realizable body colors (e.g. for paints and paints ). The infinite set of optimal colors forms the optimum color body , which within a color space representing the set of all theoretically feasible body colors. All real colors, i.e. colors with non-optimal spectra, form a subspace of the optimal color solid, i.e. lie within its limits.
The best-known example of an optimal color body is likely to be the "Rösch mountain of colors". The psychophysicist Douglas MacAdam was the first to calculate this color body and its exact limits, which is why the color body is also called MacAdam limits (German: MacAdam limits). The MacAdam limits map the optimal color body in the CIExyY color space . The exact shape or size of this color body depends on the luminance and includes all colors that can come about through scattering , reflection and refraction .
A decisive property of the optimal color body is that there is only one stimulus spectrum for each point (each color) on the surface of this body. This means that there are no metamers for all colors on the optimal color body surface . In contrast, within the body there are infinitely many metamers for every color; the further inside the color lies in the optimal color body, the greater the frequency density of its metamers.
The optimal colors are essential for the Ostwald system . As a full color, they are the full colored component, marked with the color code number N. In order to achieve the color to be identified, an additive mixture with “pure” white component w and “pure” black component s is carried out. The graduation takes place in accordance with the Weber-Fechner law .
Ostwald's color system was criticized primarily by physicists such as Kohlrausch during his lifetime , which is particularly expressed in his "remarks on so-called Ostwald's color theory".
literature
- Wilhelm Ostwald : Physical color theory . Volume 2, 2nd edition. Leipzig 1923.
Web links
Individual evidence
- ↑ Erwin Schrödinger: Theory of the pigments of greatest luminosity . Annalen der Physik, Volume 367, Issue 15, pp. 603-622