RGB Additive Colour Model
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This diagram introduces the RGB colour model. It shows the three primary colours (red, green and blue) with secondary colours between them.
What you need to remember:
- Mixing different wavelengths of light to produce other colours, is called an additive colour model or an additive approach to colour.
- Red, green and blue (RGB) are additive primary colours. This means that when these wavelengths of light are projected onto a dark surface they combined to produce other colours. The colour produced depends on the intensity of each light source.
- If wavelengths of light corresponding with all three additive primary colours are projected in equal amounts onto a dark surface the result is white.
- If wavelengths of light corresponding with all three additive primary colours are projected in unequal amounts onto a dark surface many thousands (or millions) of colours can be produced.
- Secondary colours are the colours produced when pairs of primary colours are combined in equal proportions.
Description
RGB Additive Colour Model
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About the diagram
About the diagram
- This diagram introduces the spectral colour model. Spectral colours are the colours of the visible spectrum.
- Spectral colours are evoked by a single wavelength of light in the visible spectrum. So, every wavelength of visible light is perceived as a spectral colour by a human observer.
- The spectral colour model explains why different light sources produce different experiences of colour for an observer.
What you need to remember:
- A diagram of spectral colour is usually presented in the form of a continuous linear spectrum organised by wavelength, with red at one end and violet at the other.
- The best known spectral colours are the colours of the rainbow – red, orange, yellow, green, blue and violet.
- All spectral colours are produced by a single wavelength of light.
- The fact that we see distinct bands of colour in a rainbow, rather than a continuum of colours, is an artefact of human colour vision.
- Every spectral colour is produced by a single wavelength of visible light – the small part of the electromagnetic spectrum that our eyes are attuned to.
- Spectral colours are produced as raindrops and other transparent media refract and disperse white light causing the different wavelengths to fan out into an array of colour.
- All transparent media refract and disperse light without causing scattering.
- Spectral colour is neither an additive nor subtractive colour model because each colour is produced by a single wavelength rather than by mixing different colours.
- Sunlight produces the full range of spectral colours because at the point at which light is emitted by the sun and propagates through the vacuum of space, it contains all wavelengths of visible light.
- Light containing all the wavelengths of the visible spectrum is called white light.
Spectral and RGB colours
Spectral colour should not be confused with RGB colour:
- Spectral colours are components of the visible spectrum.
- RGB colours are produced by mixing wavelengths of light corresponding with the three additive primary colours – red, green and blue.
- A diagram of RGB colour is often represented in the form of a colour wheel and shows the colours produced by mixing adjacent colours on the wheel.
What is a colour model?
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.
Why use colour models?
- Colour models help to relate colours to:
- One another
- Light sources, objects and materials
- Experience and perception.
- Colour models make sense of the fact that coloured lights, transparent inks and opaque paints (etc.) all produce different results when mixed.
- Colour models help us manage the fact that colours mean and feel different and have different associations depending on context.
- Colours models help us manage the fact that colours behave and appear differently:
- When emitted by different types of light source.
- When applied to, mixed with, or projected onto different materials.
- When used for different purposes (fabrics, electrical wiring and components, print media, movies etc.)
- When seen or used in different situations (indoors, in sunlight, in low light, on a digital display etc.)
Additive and subtractive colour
There are two principal types of colour model, additive and subtractive. Additive colour models are used when mixing light to produce colour. Subtractive colour models are used for printing with inks and dyes. The most common colour models used by graphic designers on a day to day basis are the RGB model on their computer displays and the CMYK model for digital printing.
Remember that:
- Seeing colour results from how our eyes process light waves.
- In the real world, colours are changing all the time, appear differently in different situations and are infinitely variable.
- So colour models help to make sense of a chaotic world.
What colour models do?
A colour model helps to do any of the following:
- Decide what colours to mix to get the colour you want.
- Know what happens when you mix two or more colours together.
- Provide a name or code for a colour or a series of colours you want to use again.
- Give you a list of colours produced by a rainbow or by a digital display.
- Provide a system to mix a palette of colours from red, green and blue (RGB) or from cyan, magenta and yellow (CMY).
Spectral colour model
The spectral colour model (red, orange, yellow, green, blue, violet) is associated with rainbows and the refraction and dispersion of wavelengths of light into bands of colour.
RGB colour model
RGB (red, green, blue) is an additive colour model based on the trichromatic theory of colour vision. It is widely used in video cameras, for producing colour on digital screens and with software such as Adobe Creative Cloud.
CMY(K) colour model
CMY (cyan, magenta, yellow) is a subtractive colour model. It is the standard colour model for digital printing. Printers often include a fourth component, black ink (K), to increase the density of darker colours and blacks.
HSB colour model
HSB (hue, saturation, brightness) is a popular colour model because it is more intuitive and so easier to use when adjusting colour with digital software such as Adobe Creative Cloud.
HSB is one of a family that also includes HSV (hue, saturation, value) and HSI (hue, saturation, intensity).
Applications of colour models
Colour models have many applications including:
- Understanding colour vision.
- Mixing different coloured media eg. lights, paints, inks and dye.
- Using colour with different equipment and technologies.
- Storing and sharing colour information eg. notation systems and file types.
- Describing and naming colours in a consistent way.
- Nomenclature for describing similar things eg. systems for describing birds according to their colour.
- Comparing colours eg. swatches and samples.
Colour models, colour spaces and colour systems
- Colour models are device-dependent. This means that a colour specified as R=220, G=180, B=140 might appear differently on two digital monitors or when printed by different printers with the same specifications. In other words, the exact colour produced depends on the device that produces it not on the colour model itself.
- A colour space describes the range of colours that an observer might see. Colour spaces can be very limited when a photo is printed on a low price digital printers, large when the same image is viewed on a high definition digital displays, or huge when the original scene is viewed in bright sunlight on a summer day.
- A colour system considers all the factors that affect the observer, the colour model, how information is encoded before sending to the output device and the circumstances in which it is expected to be viewed.
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.
A colour model is a system or framework used to understand, organise, and manipulate colour. It ranges from basic concepts, such as the sequence of colours in a rainbow, to more advanced models like RGB, CMYK, and CIE, which are essential for accurate colour reproduction in various fields, including digital media, printing, and manufacturing.
- A colour model, underpinned by colour theory, provides a precise and replicable approach to understanding:
- How the human eye perceives light and interprets colour.
- Different types of colour, including those produced by mixing lights, pigments, or inks.
- How to manage the diverse ways colour is processed by devices such as cameras, digital screens, and printers.
- Colour models enable us to:
- Make sense of colour in relation to human vision and the world around us.
- Use colours in logical, predictable, and replicable ways.
- Understand how to mix specific colours, whether using lights, pigments, inks, or dyes.
- Specify colours using names, codes, notations, or equations.
- Organise and apply colour for different purposes, from fabrics and interiors to vehicles.
- For more information see https://lightcolourvision.org/dictionary/definition/colour-model/
An additive colour model explains how different coloured lights (such as LEDs or beams of light) are mixed to produce other colours.
- Additive colour refers to the methods used and effects produced by combining or mixing different wavelengths of light.
- The RGB colour model and HSB colour model are examples of additive colour models.
- Additive colour models such as the RGB colour model and HSB colour model can produce vast ranges of colours by combining red, green, and blue lights in varying proportions.
- An additive approach to colour is used to achieve precise control over the appearance of colours on digital screens of TVs, computers, and phones.
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 colours.
- 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 a colour space 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.
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.
A secondary colour is created by mixing two primary colours in equal parts within a particular colour model. The colour space can belong to either an additive colour model, which combines different light wavelengths, or a subtractive colour model, which mixes pigments or dyes.
- In additive colour models such as the RGB colour model, which deals with the effects of mixing coloured light, a secondary colour results from the overlap of the primary colours: red, green, and blue. The secondary colours produced by mixing pairs of primary colours in the RGB model are cyan, magenta, and yellow.
- In subtractive colour models such as the CMY colour model, which is concerned with mixing dyes and inks, a secondary colour results from the overlap of the primary colours: cyan, magenta, and yellow. The secondary colours produced by mixing pairs of primary colours in the CMY model are red, green, and blue.
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