Color is literally in the eye of the beholder. The sensation of color is a result of the human eye’s response to light and the nervous system’s interpretation of that response.
Color perception depends on the eye’s response to light.
Through the use of color models, this complex process has been defined mathematically. The color models allow software applications (such as CorelDRAW and Corel PHOTO-PAINT) and digital devices (such as computers, monitors, digital cameras, and printers) to store, manipulate, and accurately reproduce color.
Color models, such as Lab, RGB, CMYK, and HSB, provide a systematic way of organizing and reproducing a broad range of colors from a small set of primary colors. Each color is defined numerically. The numeric values allow the colors to be interpreted, communicated, and reproduced by a wide range of devices and applications.
Each color model has a unique way of defining colors numerically.
Lab color model
The Lab color model was developed by the Commission Internationale de l’Eclairage (CIE). Unlike the RGB and CMYK color models, the Lab color model is based on how the human eye perceives color, rather than on how monitors, printers, digital cameras, and other devices reproduce color. For this reason, Lab is known as a device-independent color model. RGB and CMYK are considered device- dependent color models, because the same colors appear different when they are printed or displayed on different devices.
In the Lab color model, the range (or gamut) of all visible colors is represented as a horseshoe-shaped figure. This figure is often used as a reference for comparing the range of colors that other color models can produce. Lab is also used in color management as a reference for converting colors from one color space to another.
Lab color model
RGB color model
The RGB color model uses the components red (R), green (G), and blue (B) to define the amounts of red, green, and blue light in a given color. In a 24-bit image, each component is expressed as a number from 0 to 255. In an image with a higher bit rate, such as a 48-bit image, the value range is greater. The combination of these components defines a single color.
In additive color models, such as RGB, color is produced from transmitted light. RGB is therefore used on monitors, where red, blue, and green lights are blended in various ways to reproduce a wide range of colors. When red, blue, and green lights are combined at their maximum intensities, the eye perceives the resulting color as white. In theory, the colors are still red, green and blue, but the pixels on a monitor are too close together for the eye to differentiate the three colors. When the value of each component is 0, which signifies an absence of light, the eye perceives the color as black.
RGB is the most commonly used color model, because it allows a broad range of colors to be stored and displayed.
RGB color model. White is the result of combining the three RGB colors at their maximum intensities.
CMYK color model
The CMYK color model, which is used in printing, uses the components cyan (C), magenta (M), yellow (Y), and black (K) to define color. Values for these components range from 0 to 100 and represent percentages.
In subtractive color models, such as CMYK, color (that is, ink) is added to a surface, such as white paper. The color then “subtracts” brightness from the surface. When the value of each color component (C,M,Y) is 100, the resulting color is black. When the value of each component is 0, no color is added to the surface, so the surface itself is revealed — in this case, the white paper. Black (K) is included in the color model for printing purposes because black ink is more neutral and darker than blending equal amounts of C, M, and Y. Black ink produces sharper results, especially for printed text. In addition, black ink is usually less expensive than using colored ink.
CMYK color model. Black is the result of combining the three CMY colors at their maximum intensities.
HSB color model
The HSB color model uses hue (H), saturation (S), and brightness (B) as components for defining color. HSB is also known as HSV (with the components hue, saturation, and value). Hue describes the pigment of a color and is expressed in degrees to represent the location on the standard color wheel. For example, red is 0 degrees, yellow is 60 degrees, green is 120 degrees, cyan is 180 degrees, blue is 240 degrees, and magenta is 300 degrees. Saturation describes the vividness or dullness of a color. Values of saturation range from 0 to 100 and represent percentages (the higher the value, the more vivid the color). Brightness describes the amount of white in the color. Like saturation values, brightness values range from 0 to 100 and represent percentages (the higher the value, the brighter the color).
HSB color model
Grayscale color model
The grayscale color model defines color by using only one component, lightness, which is expressed in values that range from 0 to 255 in 8-bit images. The value range varies, depending on the bit rate of the image. Each grayscale color has equal values of the red, green, and blue components of the RGB color model.