Overlapping Beams of R & G Make Yellow

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This is one of a set of 3 diagrams showing pairs of RGB primary colours projected onto a neutral coloured surface.


In this diagram red and green primary colours overlap to produce yellow.

Understanding the diagrams:

  • The diagrams illustrate how the RGB colour model works in practice.
  • The two primary colours have the same intensity.
  • Each torch points towards a different area of the surface so they overlap.
  • The light in each case is of a single wavelength so produces a spectral colour.
  • The selected wavelengths are: red = 660 nanometres (nm), green = 525 nm.

Description

Overlapping Beams of R & G Make Yellow

TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
Additive primary colours are three wavelengths of light that produce white when combined together in equal proportions.

About the diagram

About the diagram
  • This is one of a set of 3 diagrams showing pairs of RGB primary colours projected onto a neutral coloured surface.
  • In this diagram red and green primary colours overlap to produce yellow.
Understanding the diagrams
  • The diagrams illustrate how the RGB colour model works in practice.
  • The two primary colours in each diagram are of the same intensity.
  • The light sources are arranged so that the colours overlap.
  • The light source in each case is produced by a single wavelength of light.
  • The selected wavelengths are: red = 660 nanometres (nm), green = 525 nm.
About the RGB colour model
  • RGB colour is an additive colour model that combines wavelengths of light corresponding with the red, green and blue primary colours to produce other colours.
  • RGB colour is called a model because it is a method that can be followed to produce any colour from a combination of red, green and blue light sources.
  • Red, green and blue are called additive primary colours in an RGB colour model because they can be added together to produce other colours.
  • When mixing light, each RGB primary colour is called a component of the resulting colour.
  • Different colours are produced by varying the intensity of the component colours between fully off and fully on.
  • When the light sources that produce the red, green and blue primary colours are at full intensity, together they produce white.
  • Each light source at full intensity produces a fully saturated colour.
  • When any two fully saturated RGB primaries are combined they produce a secondary colour (yellow, cyan or magenta).
  • Some applications of the RGB colour model can produce over 16 million colours by varying the intensity of each of the three component primary colours.
  • The additive RGB colour model cannot be used for mixing opaque pigments, paints or powders. To understand these colourants find out about subtractive colour models.
  •  The RGB colour model does not define the precise wavelength (or band of wavelengths) for the three primary colours.
  • When the exact composition of primary colours are defined, the colour model then becomes an absolute colour space.

Some key terms

  • A colour wheel is a circular diagram divided into segments, featuring primary colours, and used to visualize the result of colour mixing.
  • Colour wheels can enhance understanding of colour relationships and assist with the accurate selection and reproduction of colours.
  • A colour wheel starts with segments representing primary colours. Additional segments are added between them to explore the outcome of mixing adjacent primary colours.
  • By adding more segments between existing ones, further mixing of adjacent colours can be explored.
  • A colour wheel exploring the additive RGB colour model starts with red, green, and blue primary colours.
  • A colour wheel exploring the subtractive CMY colour model starts with cyan, magenta, and yellow primary colours.

White light is the name given to visible light that contains all wavelengths of the visible spectrum at equal intensities.

  • As light travels through a vacuum or a medium it is described as white light if it contains all the wavelengths of visible light.
  • As light travels through the air it is invisible to our eyes.
  • When we look around we see through the air because it is very transparent and light passes through it.
  • The term white light doesn’t mean light is white as it travels through the air.
  • One situation in which light becomes visible is when it reflects off the surface of an object.
  • When white light strikes a neutral coloured object and all wavelengths are reflected then it appears white to an observer.

Primary colours are a set of colours from which others can be produced by mixing (pigments, dyes etc.) or overlapping (coloured lights).

  • The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet. It is the sensitivity of the eye to the electromagnetic spectrum that results in the perception of colour.
  • A set of primary colours is a set of pigmented media or coloured lights that can be combined in varying amounts to produce a wide range of colour.
  • This process of combining colours to produce other colours is used in applications intended to cause a human observer to experience a particular range of colours when represented by electronic displays and colour printing.
  • Additive and subtractive models have been developed that predict how wavelengths of visible light, pigments and media interact.
  • RGB colour is a technology used to reproduce colour in ways that match human perception.
  • The primary colours used in colour-spaces such as CIELAB, NCS, Adobe RGB (1998) and sRGB are the result of an extensive investigation of the relationship between visible light and human colour vision.

The trichromatic colour model is a theory of colour that establishes terms, rules and methods to enable human colour vision to be dealt with in both systematic and practical ways.

A colour model is the how-to part of colour theory. Together they establish terms and definitions, rules or conventions and a system of notation for encoding colours and their relationships with one another.

A colour model is a way of:

  • Making sense of the colours we see around us in the world.
  • Understanding the relationship of colours to one another.
  • Understanding how to mix each type of coloured media to produce predictable results.
  • Specifying colours using names, codes, notation, equations etc.
  • Organising and using colours for different purposes.
  • Using colours in predictable and repeatable ways.
  • Working out systems and rules for mixing and using different types of colour.
  • Creating colour palettes, gamuts and colour guides.
  • To be clear about the RGB colour model it is useful to remember first that:
    • The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.
    • A spectral colour is a colour corresponding with a single wavelength of visible light, or with a narrow band of adjacent wavelengths.
    • The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet. However, because of the way the eye works, we can see many other colours which are produced by mixing colours from different areas of the spectrum. A particularly useful range of colours is produced by mixing red, green and blue light.
    • RGB colour is an entirely different approach to producing and managing colour.
  • 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 name of the model comes from the initials of the three additive primary colours, red, green, and blue.
  • Except for the three primary colours, RGB colours are not spectral colours because they are produced by combining colours from different areas of the visible spectrum.
  • RGB colour provides the basis for a wide range of technologies used to reproduce digital colour.
  • RGB colour provides the basis for reproducing colour in ways that are well aligned with human perception.
  • When an observer has separate controls allowing them to adjust the intensity of overlapping red, green and blue coloured lights they are able to create a match for a very extensive range of colours.
  • When looking at any modern display device such as a computer screen, mobile phone or projector we are looking at RGB colour.
  • Magenta is an RGB colour for which there is no equivalent spectral colour.

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