RGB colour wheel

The main purpose of an RGB colour wheel is to understand the representation and display of colour used with RGB display devices such as televisions, computers, mobile phones, cameras and the software applications used with them.

  • The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet.
  • RGB colour is a technology used to reproduce colour in a way that matches human perception.
  • An RGB colour wheel helps to simulate:
    • The effect of projecting lights with wavelengths corresponding to the three primary colours, red, green and blue onto a dark surface.
    • The additional colours produced by mixing adjacent pairs of colours i.e. adjacent primary, secondary, tertiary colours etc.

 

  • An RGB colour wheel demonstrates the gradation of colours as the number of intermediate colours between primary colours increases.
  • RGB colour wheels are particularly useful when trying to visually identify a specific RGB colour, the relationship between different RGB colours or find an RGB colour value (code).
  • The primary colours selected for RGB colours are intended to closely match those seen by an observer when white light undergoes dispersion and produces rainbow colours.
  • The bands of wavelengths corresponding with the observation of red, green and blue in a rainbow are typically:
  • Red = between 620 – 750 nanometres.
  • Green = between 495 – 570 nanometres
  • Blue = between 450 – 495 nanometres

 

  • An LED light source is often used when demonstrating the effect of projecting primary coloured lights onto a dark surface because they emit light in very narrow bands of wavelengths. The peak wavelength for the selected lights might typically be red = 625 nanometres, green = 500 nm, blue = 440 nm.
  • Typical peak wavelength of red, green and blue LED lights: red = 625, green = 500, blue =440
  • RGB colour wheels, therefore, have a minimum of three segments. These are filled with the red, green and blue additive primary colours.

 

  • When exploring RGB colour wheels the next thing to establish is what happens when pairs of primary colours of equal intensities overlap.
  • Where red and green light sources overlap they produce yellow.
  • Where green and blue light sources overlap they produce cyan.
  • Where blue and red light sources overlap they produce magenta.
  • Yellow, cyan and magenta are called secondary colours.
  • Mixtures of equal intensities of pairs of secondary colours are called tertiary colours.

 

  • Additional colours on an RGB colour wheel are produced by continuing to overlap equal intensities of adjacent pairs of colours.
  • The range of colours that can be produced by an RGB colour wheel is limited only by the system of notation and the resolution of the device they are displayed on.