HSL Model In Multimedia

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In this topic, you will learn about, HSL Model In Multimedia.

HSL Model

Color models which are presented as a sum of some primary colors are not always convenient to use. These models are not intuitive. Non- professionals can hardly understand what RGB or CMYK channels to change to make a color brighter or to change a tint. That’s why other color models were proposed. Instead of intensities of primary colors, each pixel is represented as a set of some color characteristics.

An example of such a model is HSL Model – each pixel contains Hue, Saturation, and Lightness.

Hue specifies the tint of the color. In the HSL model, the hue is represented as an angle on the color wheel. 0 degrees is considered as the red color, 120 degrees is the green color and 180 degrees is the blue color. Antipode points on the wheel (colors that are placed at the opposite points of the wheel) are called complementary colors.

Saturation is the “depth” or “purity” of the color. Low-saturated colors are close to gray, high saturated are close to the primary color. On the color wheel, saturation is specified as a distance from the center of the wheel

Lightness is the intensity of the color. Low lightness specifies that color is dark, close to black. High lightness specifies that color is close to white.

Note: too high or too low values of lightness reduce maximum saturation (black or white color cannot be close to any primary color).

This color model may seem to be device-independent, but it is not actually so. From the mathematical point of view, it is just another representation of the RGB color model. That’s why images are never stored using this color model. However, this model is often used during image processing. In particular, Graphics Mill allows us to adjust the hue, saturation, and lightness of the image (using AdjustHsl transform).

Lab Model

Lab model is a complex color model that allows for representing a wide color gamut. Lab model is device independent and its gamut includes both the RGB and CMYK gamuts, so it is extremely useful as an intermediate format for conversion between RGB and CMYK color spaces.

In Lab, each color is represented with its coordinates in the three-axis system. The first axis is Lightness, and the other two, a and b, are color axes. The lightness axis goes from black to white and all shades of grey lay exactly on this axis. a axis goes from green to magenta, where the negative b axis goes from blue to yellow, where negative values are blue, and positive ones are yellow.

Grayscale Model

There exists a special color model. It has a single channel with stores only pixel luminosity, and therefore it has no chrominance components (i.e. color information). Grayscale images typically have a special application, e.g. in medical imaging

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