RGB colour model

RGB colour is an additive colour model in which red, green and blue light is combined in various proportions to reproduce a wide range of other colours.

The human eye and light
Red, green and blue light
  • Because of the way the eye works, we can see all the colours of the visible spectrum by mixing red, green and blue lights at different intensities.
  • Red, green and blue are the three primary colours of the RGB colour model.
  • The RGB colour model replicates the response of light-sensitive cone cells in the retina at the back of our eyes sense colour.
  • Mixing wavelengths of light corresponding with the RGB primaries fools the eye into seeing almost any imaginable colour.
Trichromatic colour vision (Trichromacy)

The trichromatic colour theory explains the system the human eye uses to see colour.

  • Trichromatic colour theory is based on the presence of three types of light-sensitive cone cells in the retina at the back of our eyes, each sensitive to a different spread of colour.
  • All the colours we observe result from the simultaneous response of all three types of cones.
  • The sensitivity of cone cells is the physiological basis for trichromatic colour vision in humans.
  • The fact that we see colour is, in the first instance, the result of interactions among the three types of cones, each of which responds with a bias towards its favoured wavelength within the visible spectrum.
  • The result is that the L, M and S cone types respond best to light with long wavelengths (biased towards 560 nm), medium wavelengths (biased towards 530 nm), and short wavelengths (biased towards 420 nm) respectively
RGB and digital devices
  • RGB colour is deeply embedded in many contemporary technologies.
  • When looking at any modern display device such as a computer screen, mobile phone or video projector we are looking at RGB colour.
  • RGB colours are produced:
    • On a computer or mobile phone screen:  By Juxtaposing tiny dots of light corresponding with the three primary colours, red, green and blue.
    • On a digital projector: By projecting three carefully aligned but separate images, one red, one green and one blue onto a screen.
  • When an observer has separate controls allowing them to adjust the intensity of overlapping red, green and blue RGB primary coloured lights they are able to create a match for an extremely wide range of colours.
RGB colour model in practice
  • RGB colour model works in practice by asking three questions of any colour: how red it is (R), how green it is (G), and how blue it is (B).
  • The RGB model is popular because it can easily be used to produce a comprehensive palette of 1530 vivid hues simply by adjusting the intensity of the three primaries.
  • When the saturation or brightness of a hue needs to be adjusted it is sometimes easier to switch to the HSB colour model.
RGB colour values
  • RGB colour values are expressed as decimal triplets (yellow = 255, 255, 0) or hexadecimal triplets (green = #00FF00 ) and are used in software applications to select specific colours.
  • In both cases, the triplets determine the amount of red, green and then blue used to produce a specific colour.
  • A decimal triplet is made up of three numbers between 0 and 255 divided by commas. A hexadecimal triplet starts with a # sign followed by three two-digit numbers with values between  00 and FF written without spaces between.
References
  • https://en.wikipedia.org/wiki/Comparison_of_color_models_in_computer_graphics