Color value
The color value is the absolute value of the vector for a color location .
Explanation
A three-dimensional color valence can be assigned to every color stimulus , i.e. every stimulus that triggers color perception . This three-dimensionality is based on Graßmann's First Law ; This means that color spaces can be represented with three coordinates, except for special requirements. So three values are sufficient to describe a color in its perception.
The three coordinates of such a measuring space can be determined by three calibration valences (suitable basic values); these can in turn be converted into basic colors using three suitable light emitters . All colors can be generated by additive color mixing of these three (initially theoretically determined) calibration valences .
Such additive color mixing follows the rules of vector addition , which is why Schrödinger introduced vector representation in color measurement . The color vectors are pointers in the coordinate system with a defined direction and a certain value. In the standard valence system , the basic directions are the vectors of the calibration valences X, Y, Z. These are also referred to as tristimulus values and are chosen so that only positive color values occur.
In such a color system , the black point necessarily lies at the coordinate origin {0,0,0}, i.e. neither red nor green nor blue. The color valence determines the position vector (i.e. the connecting line in a three-dimensional space) from this black point to the color location . The direction of this position vector is the chrominance , and the length of this vector is the color value.
Standard color values
The standard color values X, Y, Z are internationally agreed as basic calibration values in the standard color system .
Y is also defined in such a way that it is also a measure of the brightness of the color . For body colors , this value should better be referred to as the lightness reference value A = Y, since the relative brightness has an effect here.
In the case of light sources , the standard color values are determined from the standard spectral value functions and the spectral properties of the lamps. For standard illuminants , the standard spectral values are recorded in tables.
Standard color value proportions
Standard color value components x, y, z are standardized sizes of the standard color values related to the sum of X + Y + Z for the representation of the color location in the standard color table :
It is therefore sufficient to specify x and y, since z results arithmetically. With these two values (as part of the color valence) the color type is determined.
literature
- Manfred Richter: Introduction to colorimetry. Walter de Gruyter, Berlin 1981
Web links
- Tables of standard color values, applets for visualization
- Standard color value tables, tristimulus values, chromaticity values