Perceptual color models

from Wikipedia, the free encyclopedia

Perceptual color models are color models that are not technically-physically but perception -oriented. On the one hand, there are models in which colors are mixed from other colors (e.g. RGB , CMYK ) and, on the other hand, there are perceptual color models that describe colors using the characteristics of brightness , saturation and hue . There are different perceptual color models that differ in their structure. The best known are the HSI, HSV and HLS models (Hüppi / Kuhn 2000). For differences between the individual HSx color spaces, see HSV article .

The RGB model represents colors as an additive color mixture of red, green and blue, whereas in perceptual models colors differentiate between the color information (hue and saturation) and the brightness information (also referred to as intensity) (Bulaova 2002).

While in additive and subtractive color systems the brightness, saturation and hue automatically shift with the change of a color channel , in perceptual color systems hue, color saturation and lightness are independent characteristics of a color and can be edited individually. Since this type of color representation meets human perception and is intuitively understandable, it is used in graphics programs where the user is offered the possibility of interactive color changes.

Perceptual color models are described by cylindrical coordinates . The base area is shown as a color wheel in some publications and as a color hexagon in others. The gray value axis, whose values ​​are given in percent, runs perpendicular to the base area through its center. Here 0% stands for very dark colors and 100% for very light colors. Changing the brightness value corresponds to removing or adding white or black. In the color wheel (or color hexagon) the saturation decreases from the outside to the inside. Like the brightness, it is given in percent (Pandit 2001).

The color arrangement of the color wheel / hexagon is due to the arrangement of the RGB cube . The RGB color space is rotated so that black (0/0/0) points down and white (1/1/1) points up. A hexagon is created by projecting the cube onto a plane (Schnabel 1999). Each color takes a corresponding position in the color wheel, whereby all colors can be clearly described by their number of degrees: pure red corresponds to 0 °, pure yellow corresponds to 60 ° etc. (Schurr 2000). A change in a color tone leads to a shift in the entire color spectrum, with the color tones moving by the respective number of degrees along the color wheel. The colors in the marked area change accordingly during image processing.

swell