CMYK printing process, Color model Lab - Informatics for the humanities

CMYK printing process

When printing on many devices (color laser printer, offset or silkscreen printing machine, etc.), either a layer of paint of a strictly specified thickness is placed at each individual point, or an unpainted substrate is left. To reproduce halftones, the image is rasterized, i.e. is represented as a collection of color points C, M, Y and K, the density of which determines the percentage of each ink . Points close to each other visually merge, colors are superimposed on each other. From the blending of colors, the given shade is obtained.

Numeric values ​​in CMYK and their conversion. Each of the numbers defining the color in CMYK represents the percentage of the paint of the given color that is the color combination, or rather the size of the dot of the raster. It is important to note that the numerical value of the paint in CMYK can not itself describe the color. The numerical values ​​of CMYK are just a set of hardware data used in the printing process to form an image, and do not define the color unambiguously. The color model CMYK 255 is especially emphasized. The essence of the model: each color is described by gradation not from 0 to 100, as in the classical CMYK model, but from 0 to 255. In comparison with RGB, CMYK has a smaller color coverage.

Lab Color Model

Lab - is an abbreviation for the names of two different (albeit similar) color spaces. More known and common is CIELAB (more precisely, CIE 1976 L * a * b *), other - English. Hunter Lab (more precisely, Hunter L , a, b ). Most often, when talking about Lab, , you mean CIELAB. When developing Lab strong> the goal was to create a color space, the color change in which will be more linear in terms of human perception (compared to XYZ), i.e. so that the same change in the values ​​of the color coordinates in different areas of the color space produced the same sensation of color change. Thus, the nonlinearity of the perception of color by a man would be mathematically adjusted. The Lab model is unique because it's hardware independent. In the RGB and CMYK models, colors are described as numeric values ​​for the correct display, without taking into account the hardware and environment changes that determine the actual color display. The Lab model is constructed according to the actual color definition and its state in different environments.

For reference

The basics of the color model Lab. The basic idea of ​​the Lab color model is this. Although our eye is most sensitive to colors such as red, green and blue, we will not be able to recognize the different colors until three additional nerve signals are registered in the brain: the "purple-green" link, the link "yellow-blue" and a luminance relationship (otherwise referred to as a "black-white" link). Purple does not contain green, yellow does not contain blue, and white does not contain black. In the Lab model, it is assumed that any perceivable color can be described by specifying, with the help of numbers, its position in these components. When the specification Lab is used to calculate certain lighting conditions, they can be further refined based on the response of the human vision to them.

In the color space Lab , the value of lightness is separated from the value of the chromatic component of color (top, saturation). Therefore, Lab is an abbreviation of the three color space components used. Lightness (illumination - lightness ) is specified by the L coordinate (varies from 0 to 100, i.e. from the darkest to the lightest), the chromatic component - by two Cartesian coordinates a and b ( < strong> and is the color position in the range from green (English green ) to red/magenta (English red/magenta )) , and b - its position between the blue English blue ) and yellow ( yellow ) .

Unlike RGB or CMYK color spaces, which are, in fact, a set of hardware data for color reproduction on paper or on a monitor screen, Lab uniquely identifies the color. Therefore, Lab is widely used in image processing software as an intermediate color space through which data is converted between other color spaces. In this case, the special properties of Lab made editing in this space a powerful tool for color correction. Lab provides the ability to selectively affect the brightness and individual colors in the image, enhance color contrast, remove digital noise.

Lab - one of the most common models in printing. With any transformation of an image from one color model to another, an internal conversion to the Lab model is first performed. > is used by most hardware-independent color management systems,

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