RGB Colour Wheel with 18 Colours – Disc

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This is one of a series of diagrams exploring RGB colour wheels. Colour wheels demonstrate or simulate the effect of colour mixing.


Colour wheels can be used to explore the effect of mixing any type of colour. Light, inks, dyes, artist’s paints, pigments and colourants all produce other colours when mixed together.

Whilst a colour model outlines a method for mixing and using different types of colour, a colour wheel explores what happens in practice.

Description

RGB Colour Wheel with 18 Colours

TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
RGB refers to the colours red, green and blue. These are the primary colours used by the RGB colour model to mix wavelengths of light to produce a palette of as many as 16 million colours.
Red, green and blue are the three additive primary colours used in the RGB colour model.
No! The colours produced by mixing primary colours are not spectral colours. Spectral colours are produced by a single wavelength of light.
Blue and red are the two primary RGB colours that together make magenta!

About the diagram

This is one of a series of diagrams exploring RGB colour wheels. Colour wheels demonstrate or simulate the affect of colour mixing.

Colour wheels can be used to explore the effect of mixing any type of colour. Light, inks, dyes, artist’s paints, pigments and colourants all produce other colours when mixed together.

Whilst a colour model outlines a method for mixing and using different types of colour, a colour wheel explores what happens in practice.

Understanding the diagram

  • A colour wheel fills the centre of the diagram and in this case has three segments showing the three RGB primary colours with five intermediate colours between each one.
  • The RGB codes corresponding with each colour appear to the left of the wheel and continue on the right.
  • Notice how the colour notation works:
    • Three numbers (separated by commas) show how much red, green and blue light is used to produce each colour.
    • The minimum value for each light source is 0. In this case the light is fully off.
    • The maximum value for each light source is 255. In this case the light source is fully on.
    • As each number increases so does the intensity of the corresponding light but the wavelength and so the colour we see stays the same.
RGB colour values
Light source Red Green Blue
Maximum value for each light source (fully on) 255 255 255
Values between 0 and 255 1 to 254 1 to 254 1 to 254
Minimum value for each light source (fully off) 0 0 0

What is an RGB colour wheel

  • The purpose of an RGB colour wheel is to demonstrate or simulate the effect of projecting coloured lights, corresponding with the additive primaries (red, green and blue), onto a dark surface.
  • In laboratory conditions, light sources are of equal intensity when fully on but can be turned down in 256 equal steps till fully off. The wavelengths of the light they output are set to values such as:
  • When coloured lights are projected and focused onto a surface they form overlapping circles. Colour wheels however are usually divided into segments like the spokes of a wheel on a bicycle.
  • For everyday purposes, the most straight forward way to explore the RGB colour model is on a computer using software that allows different RGB colours to be selected.
  • RGB colour wheels have a minimum of three segments. These are filled with the red, green and blue additive primary colours.
  • When exploring RGB colour wheels the first thing to establish is what happens where 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 a red light sources overlap they produce magenta.
  • Yellow, cyan and magenta are called secondary colours and fill the segments between the primary colours on a colour wheel with six segments.
  • Mixtures of equal intensities of pairs of secondary colours are called tertiary colours on a colour wheel with twelve segments.
  • Additional colours are produced by continuing to overlap equal intensities of adjacent pairs of colours.
  • The range of colours that can be produced on a computer screen by an RGB colour wheel is limited only by the system of notation, the resolution of the device they are displayed on and by the ability of an observer to distinguish between similar colours.

About RGB colours

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.
  • In computer software and apps by selecting RGB colours using swatches or by selecting RGB colour values (codes) using decimal or hexadecimal notation.

Look at a computer screen or TV using a magnifying glass to see the three RGB primary colours. Then step back to see how different colours appear when all the pixels merge together.

RGB and spectral colour

RGB colour values

RGB colour values are represented by decimal triplets (base 10) or hexadecimal triplets (base 16). These are used in software and apps to select a colour.

In decimal notation, an RGB triplet is used to represent the values of red, then green, then blue.

A range of decimal numbers from 0 to 255 can be selected for each value:

  • Red = 255, 00, 00
  • Yellow = 255, 255, 0
  • Green = 00, 255, 00
  • Cyan = 00, 255, 255
  • Blue = 00, 00, 255
  • Magenta = 255, 00, 255

In hexadecimal notation an RGB triplet is used to represent the value of red, then green, then blue. A range of hexadecimal numbers from 00 to FF can be selected for each value.

The hash symbol (#) is used to indicate hex notation:

  • Red = #FF0000
  • Yellow = #FFFF00
  • Green = #00FF00
  • Cyan = 00FFFF
  • Blue = #0000FF
  • Magenta = #FF00FF

The sequence of hexadecimal values between 1 and 16 = 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E and F.

The sequence of hexadecimal values between 17 and 32 = 10,11,12,13,14,15,16,17,18,19,1A,1B,1C,1D,1E and 1F.

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 precise wavelengths (or band of wavelengths) for the three primary colours.
  • When the exact composition of primary colours are defined, the colour model then describes an absolute colour space.

Some key terms

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.

  • 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.

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.

secondary colour is a colour made by mixing two primary colours in a given colour space. The colour space may be produced by an additive colour model that involves mixing different wavelengths of light or by a subtractive colour model that involves mixing pigments or dyes.

  • 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.

ROYGBV is an acronym for the sequence of hues (colours) commonly described as making up a rainbow: red, orange, yellow, green, blue, and violet.

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