# Achromatic

Parasol in achromatic colors
Parasol in bright colors
The achromatic straight line is the central axis in this color model

A color is said to be achromatic if it has neither a specific hue nor saturation . Achromatic colors are black , gray and white . The more precise restriction is necessary for general usage because they have no color cast . Achromatic colors differ from one another only in their lightness value . Depending on the brightness, there are gray levels .

"Achromatic - neutral light sensation as a result of the mixture of all wavelengths of the spectrum in physically the same radiation strength "

The chroma of the achromatic colors is by definition zero. With increasing chroma, the optimal colors result , which in a suitable case are the spectral colors .

Achromatic is to be regarded as a color. Manfred Richter derives this from the fact that two surfaces even differ if they are just differently bright. Color is the property that distinguishes two unstructured adjoining surfaces when viewed with one eye without moving the eye.

“That may seem strange to some [...]. But once he has the experience that a certain brown differs from a certain orange only in its lightness (ie the orange can be made exactly the same by darkening to that brown), he will see the correctness of the assertion that two Surfaces of different brightness just show two different colors, because who will describe orange and brown as two identical colors? So two different light grays are two different colors. "

- Manfred Richter

The color stimulus achromatic colors produces a color valence which has the same numerical value for all three color coordinates; all three color-sensitive cones are stimulated with the same intensity. The size of the intensity results in the position on the achromatic straight line between black = 0% and white = 100%.

• The achromatic straight line is the neutral curve that is also present in this form in some color models . In the L * a * b * system it is the L * axis which is represented by the points with the coordinates a * = b * = 0. In the HSB rooms, the achromatic colors are located along the light value axis or, depending on the respective description, along the axis of the dark levels.
• The achromatic point is in the middle of the CIE chromaticity diagram . It has the coordinates x = y (= z) = 0.333. The distance between a color point corresponds to the saturation of its color valence. The achromatic point is the equivalence point of the chromaticity diagram (chromaticity diagram), while the white point lies on a curve depending on the color temperature .

## Application / use

In principle, color can be seen as a free or bound color:

• the free color appears to the eye purely flat
• the bound color is bound to a surface and has a structure.

### photography

Achromatic colors are important in (color) tone-free black and white photographs . The eye reacts strongly to deviations from neutral gray , so tints are annoying. An example of this is described in the article paper . In artistic photography , the achromatic colors play a special role, as it is abstracted from the color.

### pressure

The achromatic colors play a role in the CMY system , especially in four-color printing . Here the limitation of the material properties of the three colored pigments for cyan , magenta and yellow is eliminated with the achromatic color black. Instead of mixing the color depth insufficiently, a print run with black pigment is carried out.

By the same mixture of complementary colors to obtain the corresponding Unbuntfarbe because the coloring of the two complementary colors in cancels "Sättigkeit" and chromaticity. In real applications, however, the exact contradiction can cause difficulties.

### Analog television

The term achromatic is within the scope of test signals of analog television technology used: Unbuntfelder are two areas of an electronic test image for the PAL - color television system . There a faulty color carrier signal is generated electronically , which should be decoded to a gray by a correctly balanced television (more precisely: by its PAL decoder ). Incorrect adjustment leads to color casts in the achromatic fields.