Gray axis

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The gray axis describes the specific distribution of bright colors in a color mixing system , which leads to neutral gray color impressions .

CMYK

In CMYK , the gray axis refers to the cyan , magenta and yellow combinations, which result in a gradient running from white to gray to black, which is achieved exclusively from the mixed colors , i.e. H. without adding black.

In offset printing , due to the physically suboptimal nature of the printing inks, an overhang of around 10% cyan compared to the almost identical proportions of magenta and yellow is necessary in order to achieve a neutral gray in the printed result.

The control of the gray axis is one of the most important control parameters in printing , as it influences the entire image mood. A stronger application of color of a primary color not only causes a stronger coloring of this primary color, but also a shift of the gray axis in the direction of this basic color .

Separations with strong to maximum GCR or UCR are resistant to such a shift , since in this case all colors in the vicinity of the gray axis are realized exclusively by the printing color black. On the other hand, this has the disadvantage that at maximum GCR no corrections on the printing machine are possible if everything was separated in prepress to a gray axis that does not perfectly match the printing system .

CMYK ICC

In CMYK- ICC profiles that are used for separation, in addition to tone value increase , the parameters of the UCR or GCR, the course of the gray axis is also permanently implemented.

RGB

In RGB color spaces , the gray axis usually runs along the value combinations with equal proportions (R = G = B). But that can also be different, e.g. B. in systems with separate light sources for the channels or in scanner profiles due to unevenly strong filtering .

L * a * b *

In the L * a * b * color model , the gray axis runs by definition along the L axis ( luminance or brightness ) with a * = 0 and b * = 0.

LCH and HSB

In the  LCH and HSB color models, the gray axis runs along the value 0 for the saturation component contained there (C for chroma in the LCH and S for saturation or saturation in the HSB).