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Colour Models

RGB Colour Model (red, green, blue)
Used for the Internet, TV screens and computer monitors.

In the RGB system, the red, green and blue dots are assigned brightness values along some scale, for example 0 to 255, where 0 is dark and 255 is bright. By listing the three values for the red, green and blue phosphors, you can specify the exact colour that will be mixed.

Additive colours get lighter when mixed. As each component of light is mixed in, the combination becomes a new colour. Red, green and blue are the three additive primaries. You can mix any colour of light with different combinations of the additive primaries. When you mix all three together in balanced amounts, you get white.

These three primaries are the basis of the additive colour model. It's called the RGB model, and it's usually used to create colour on your computer display as well as other electronic devices. By mixing together various amounts of red, green and blue light, you can make almost any colour. The RGB colour space is a multi-coloured cube with different points showing what colours different mixtures of red, green, and blue make.

Television screens and computer monitors make their colours by mixing red, green and blue lights. A monitor or television screen mixes a colour by illuminating tiny dots of red, green and blue phosphors with an electron gun located at the back of the monitor. By illuminating each of the dots to a different brightness, the monitor creates different colours.

Because the RGB model is only capable of producing a certain range of colours, there are some colours that cannot be reproduced accurately by a computer monitor. The number of colours visible on a monitor is further reduced by the limitations of the video hardware in the computer, which may display anywhere from just black and white up to 16.7 million colours.  

HSL Colour Model (Hue, Saturation, Luminance)

The HSL model is very similar to the RGB model. In fact, when they're expressed mathematically, they're identical. The difference lies in how colours are expressed numerically. The hue determines which basic colour it is. Red, green, blue, yellow, orange, etc. are different hues. Saturation and luminance tell more about the variations of these basic colours. Saturation is the vividness (or "purity") of the colour, i.e., how much of the colour's complement is mixed in. Finally, luminance refers to the "whiteness" of the colour. It may also be termed "brightness," "value" or "intensity."

Other models related to the HSL model are the HSB (Hue, Saturation, brightness) and HSI (Hue, Saturation, Intensity) models. These terms are all similar but not interchangeable.  

CIE Colour Model  (Commission Internationale l'eclairage)

The CIE model is a more subjective description than the others. In 1931, the Commission Internationale l'Eclairage tested many people and found that the sensitivity of the receptors in the eye caused certain colours to be associated with others. The CIE colour space includes all visible colours, whether or not they can be defined in the RGB or CMYK models. Computer printers and other devices for displaying colour have practical limitations that prevent them from making ALL of the visible colours. The colours that they CAN create are collectively called the colour gamut. The CIE model is useful in part because a printer's colour gamut can be drawn on the CIE colour space showing what colours cannot be printed. Other colour models closely related to CIE are UCS (Uniform Colour Space), CIELAB and CIELUV.

PANTONE Matching System  See pantone  

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