RGB colour model

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

RGB colour model in practice
  • The RGB colour model works in practice by asking three questions of any colour: how red is it (R), how green is it (G), and how blue is it (B).
  • The RGB model is popular because it can easily produce a comprehensive palette of 1530 vivid hues simply by adjusting the combination and amount of each of the three primaries it contains.
  • When the saturation or brightness of a hue needs to be adjusted it is sometimes easier to switch to the HSB colour model.
Hardware applications of the RGB colour model

The RGB colour model is deeply embedded in many contemporary forms of hardware and is the industrial standard for capturing colour on cameras or scanners and reproducing colour on TVs, phones, computers and projectors.

  • RGB sensors are used in cameras, scanners, phones, optical mouse devices, medical imaging equipment, and night-vision equipment such as thermal imaging devices, radar, sonar, and others.
  • Both analogue and digital image sensors can detect, capture and convey the colour information needed to produce images.
  • When viewing images using contemporary displays such as computer screens, mobile phones and video projectors we are looking at digital information conveyed by the RGB colour model.
  • RGB colour is produced on computer or mobile phone screens by juxtaposing tiny dots of light corresponding with the three primary colours, red, green and blue.
  • RGB colour is produced on digital projectors by projecting three carefully aligned but separate images, one red, one green and one blue onto a screen.
  • In the RGB colour model, each primary colour is typically represented by 8 bits (256 levels of intensity), allowing for a total of over 16 million possible colours.
  • The RGB colour model forms the basis for creating images in digital formats such as JPEG, PNG, and GIF.
  • RGB technologies used to create displays in use today include:
    • Liquid crystal display (LCD) and thin-film transistor (TFT) LCD.
    • Light-emitting diode (LED), Quantum dot (QLED), OLED, AMOLED and Super AMOLED display
Software applications of the RGB colour model

In the implementation of the RGB colour model used by Illustrator in Adobe CC:

  • The RGB colour model is the default setting in the Colour Panel. If the colour panel is not visible then look for Colour in the Windows menu.
  • Use the hamburger menu in the top right of the panel to change from the default RGB to other colour models.
  • The amount of red, green and blue in a colour can be adjusted using the corresponding sliders or by inputting a value between 0 and 255 for each colour.
  • However, there are easier ways to select a colour in the RGB colour model:
    • Select a colour by clicking anywhere on the RGB Spectrum right below the sliders and then make fine adjustments using the sliders.
    • Use a colour picker app to find the colour you want and paste its hexadecimal value into the Colour Panel.
    • Build your own library of swatches and save them into the swatches panel.
    • Open an existing document that contains all the colour swatches you need, Save as using a different file name and then delete the previous content. This way you start with a blank document but all the settings and colours used last time are retained.
    • Switch to the HSB colour model using the hamburger menu in the Colour Panel and adjust the hue, saturation and brightness of a colour.
RGB colour notation
  • The RGB colour model uses both decimal and hexadecimal triplets for colour notation. So RGB decimal and hexadecimal triplets look like this:
    • R = 255, G = 128, B = 0 is the decimal notation for orange.
    • #FF8000 is the hexadecimal notation for orange.
About the human eye, light and RGB colour
  • The human eye, and so human perception, is tuned to the range of wavelengths of light that make up the visible spectrum and so to the corresponding spectral colours between red and violet.
  • The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.
  • To be exact, spectral colour is a colour corresponding to a single wavelength of visible light, but in everyday terms, spectral colours are usually composed of a narrow band of adjacent wavelengths.
  • Because of the way the eye works, we can see all the colours of the visible spectrum when red, green and blue lights are combined at different intensities.
  • The RGB colour model is designed to provide the exact stimuli to the light-sensitive cone cells in the retina to illicit perception of any predetermined colour.
  • Mixing wavelengths of light corresponding with the RGB primaries enables the human eye to see almost any imaginable colour including colours such as magenta that are not part of the visible spectrum.
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About 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.
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References
  • RGB colour is an additive colour model in which red, green and blue light is combined to reproduce a wide range of other colours.
  • The primary colours in the RGB colour model are red, green and blue.
  • In the RGB model, different combinations and intensities of red, green, and blue light are mixed to create various colours. When these three colours are combined at full intensity, they produce white light.
  • Additive colour models are concerned with mixing light, not dyes, inks or pigments (these rely on subtractive colour models such as the RYB colour model and the CMY colour model).
  • The RGB colour model works in practice by asking three questions of any colour: how red is it (R), how green is it (G), and how blue is it (B).
  • The RGB model is popular because it can easily produce a comprehensive palette of 1530 vivid hues simply by adjusting the combination and amount of each of the three primaries it contains.