LMS color space
The LMS color space is the effective color space for every human observer of colored lights or colored surfaces . It is a physical-mathematical representation of the underlying biological - psychological process of color perception . The LMS color space is the actual pin color space and basis for lifelike color reproducing technical systems.
The abbreviations
meaning
The color receptors or cones of each eye have an individual spectral sensitivity. This is formed into a certain sensory impression in the nervous system in the perception process. This applies to every eye, whether animal or human, and the subsequent nervous system.
Every person with normal color vision has three types of color-sensitive cones. These are called L-, M- and S-cones according to the position of the maximum of their sensitivity, in German-language literature K-cones are sometimes used for S-cones:
- the L cones take priority to the color stimulus of the radiation from the l angwelligen red region true (engl. long wavelength )
- the M cones the m ittleren green region (engl. medium wavelength )
- the S / K-pin the k urzwelligen blue region of the spectrum (engl. short wavelength ).
To the receiving system of the visual sense are also the chopsticks , English: rods .
Alternative abbreviation
| according to the type of cone or the wavelength of the radiation received |
according to the position of the maximum sensation * |
with Greek letters |
according to color ametropia or failed color receptor (cones) |
|---|---|---|---|
| L ( long ) | R (for red ) | ρ (rho) | P ( protanopia ) |
| M ( medium ) | G (for green ) | γ (gamma) | D ( deuteranopia ) |
| S ( short ) or K (short) | B (for blue ) | β (beta) | T ( tritanopia ) |
'*) can lead to confusion with the coordinates of the RGB color space .
theory
All colors can be represented (for a human observer) by three basic colors according to Grassmann's first law . Therefore, each color nuance can be assigned a color location in a three-dimensional vector space . This approach is the abstract symbolism that became necessary for coloring methods, colorimetry and technical treatment of colors, such as the color rendering of this screen. Color spaces are adapted to different tasks and as CIE color space , RGB color space , CMYK or LAB color space in use.
Radiation in the visible range directly from a light source or indirectly from a surface exerts a color stimulus . This causes a color valence , a color value , in the three cones of the human visual organ . In the subsequent process in the body, this is perceived as a color tone . The term tristimulus is used for the “stimulated” reaction of the color centers , although this term is also used for the modified standard valences .
For illustration, the "spectral valences" of the cones are shown in the diagram. The values were measured directly on human L, M and S cones as well as on human rods with a microscope spectrometer . In addition, the measured values on rhesus monkeys carried out by Bowmaker are entered.
Despite individual differences in the spectral absorption properties of these cones, which are caused by genetic variations , and the specific influence of the lens or vitreous humor in the eye, which is determined by personal coloring or, for example, by cloudiness in old age , the absorption curves for all normal-sighted people agree well .
The totality of the perceptible color stimuli, i.e. the colors, is ultimately mapped to these three sizes L, M and S. In the “objective world” there are spectral distributions that correspond to color stimuli with an intensity of 0% to 100% for each (even continuously stepped) wavelength between approx. 380 nm and 780 nm.
Mathematical description
A three-dimensional vector space can be formed, which is spanned by the three axes L, M, S:
- (... alternatively also )
The irradiated color stimulus striking the eye has the spectral composition f (λ), the receiving cones absorb with the spectral values l (λ), m (λ) and s (λ). These ( cone ) spectral values are the color values in the color equations and result in the spectral color valences:
Depending on the interpretation, you get the color valence sent to the nervous system with the necessary three color values or the color location of the color in the color space.
In colorimetry, a spectral color is a sufficiently narrow section of the electromagnetic spectrum with a bandwidth Δλ of almost 0 nm ; in practice this width can be a minimum of 1 nm.
Location in the color table
Since the sensitivity curves of the cones of the human eye cannot generally assume negative numerical values, the three spectral value functions of the LMS system must also have exclusively non-negative values.
This is only possible if all spectral colors (and thus all other real colors) exclusively by internal mixture of the Grundvalenzen , , can be matched. The three basic valences must therefore span a gamut triangle which completely surrounds the spectral color range, i.e. which itself lies outside the spectral color range . They are therefore (similar to the standard valences ) virtual primary valences .
Each of them corresponds to the color valence that the associated color receptor species would “see” if it were stimulated on its own. Because of the overlap of the sensitivity ranges, however, it is not possible to stimulate one type of receptor alone, and none of the fundamental valences can actually be generated.
History
these are the tristimulus curves in X, Y, Z
Measuring the absorption spectra L (λ), M (λ) and S (λ) individually is complex. The foundations for the CIE systems were laid by the measurements and work of Maxwell , König , Dieterici and Abney , which were summarized in 1922 by the OSA ( Optical Society of America ) and published in edited form.
Since the possibilities and the accuracy of the measurements were inadequate at that time, David Wright (1928) and John Guild (1931) carried out new and more precise color matches and photometric comparisons independently of one another , thus creating a new database. Your two data sets agreed very well with each other and also confirmed the older measurements in terms of accuracy. In 1931, Wright's and Guild's data were recommended internationally as a database by the CIE .
Stiles, Burch, and Speranskaya later provided additional data that also confirmed Wright and Guild's measurements and expanded the system.
Bowmaker finally carried out measurements of the absorption properties of the cones directly on the object using a microscope spectrometer . It was shown that the LMS sensitivities, which were previously only indirectly calculable, corresponded very well with the measurement results, i.e. the actual values.
Since the original LMS color space has some disadvantages for technical purposes, the cone valences LMS were replaced by the virtual standard valences XYZ and the CIE standard 1931 was used as a basis.
A further disadvantage and potential source of error is still considered to be that the number of individuals was limited to 17 selected persons for the technical reasons of the 1930s and Guild only carried out measurements on 7 of them. Nevertheless, in 1955, in subsequent measurements, Stiles found that the data from the 17 people represent and guarantee an adequate representation of the 2 ° standard observer. However, since the CIE standard values have prevailed today, corrections are mainly made with transformations such as the DIN99 color space using computer technology.
To take into account all normal-sighted observers who deviate from the standard observer, there are data sets that supplement the CIE data ( standard deviate observer ) and that apply to both the 2 ° and the 10 ° standard observer.
literature
- Manfred Richter: Introduction to colorimetry. Walter de Gruyter, Berlin 1976.
Individual evidence
- ↑ The diagram is based on the measured values by Bowmaker and Mollon, which were published in 1983.
- ↑ The diagram is based on Bowmaker's measurements from 1983.
- ↑ David L. MacAdam: Color Measurement 2nd ed. Springer-Verlag - chap. 1.4 "Color Specification in Terms of Equivalent Stimuli"
- ^ RWG Hunt: Measuring Color . Ellis Horwood Ltd. 1987 - p. 44
- ↑ RWG Hunt: Measuring Color , Ellis Horwood Ltd. 1987. - Table 7.1 "Modifications of CIE color-matching functions to obtain a standard deviate observer"
