Colour model

Whilst a colour theory is a body of knowledge that explains observations regarding the behaviour of colour in a particular context, a colour model is a method of putting those ideas into practice.

  • A colour model derived from a colour theory is the how-to part of exact and reproducible approach to:
    • The way the human eye responds to light and experiences colour.
    • Managing different types of colour such as the colours produced by lights, pigments and inks.
    • Deal with the different ways colour is handled by equipment such as camera, digital screens and printers.
  • Whether or not we recognise it, whenever we are working with colour, we are adopting a colour theory, a colour model and a colour space.
  • A colour theory and related colour model can be used to establish terms and definitions, rules or conventions and systems of notation for encoding colours and managing their relationship with one another.
  • The most practical colour models are part of everyday life and enable accurate input and output of colour information to TVs, computers, phones and printers.
  • Widely used colour models include:

A colour model enables us to:

  • Make sense of colour in relation to human vision, to the world we see around us.
  • Use colours in logical, predictable and repeatable ways.
  • Understand how to mix a particular colour from light or pigments, inks and dyes to produce predictable results.
  • Specify colours using names, codes, notation, equations etc.
  • Organise and use colour for different purposes and in different contexts, eg. on fabrics, interiors or vehicles.
Why use colour models?
  • Colour models help to relate colours to:
    • One another
    • Light sources, objects and materials
    • Perceptions and experiences.
  • Colour models make sense of the fact that coloured lights, transparent inks and opaque paints (etc.) all produce different results when mixed.
  • Colours models help us manage the fact that colours behave and appear differently:
    • When emitted by different types of light source.
    • Depending upon the type of media – inks, dyes, pigments.
    • When seen or used in different situations (indoors, in sunlight, in low light, on a digital display etc.)
    • When applied to, mixed with, or projected onto different materials.
    • When used for different purposes (fabrics, electrical wiring and components, print media, movies etc.)
About additive and subtractive colour models

There are two principal types of colour models, additive and subtractive.

About colour models, colour spaces and colour systems
  • A colour model is usually device-dependent. This means that the exact colour produced by a model depends on the device that reproduces it. So a colour specified as R = 220, G = 180, B = 140 might appear differently on two digital monitors or when output by different printers.
  • Once a colour model has been selected then a colour space defines the range of colours available within a specific workflow and may be determined by a user or programmatically. Colour spaces may be relatively small when printing a photo on a low-price digital printer, large when the same image is viewed on a high-definition digital display, or huge when the original scene is viewed in bright sunlight on a summer day.
  • A colour management system considers all the factors that affect how the colours in a scene or image are dealt with from start to finish of their reproduction. Factors include how an image is captured, how information is encoded, how it is edited, how and where it will be reproduced and viewed.
RGB colour model

RGB (red, green, blue) is an additive colour model and is closely related to the trichromatic theory of colour vision. It is widely used in digital 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. Digital printers usually use 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 additive colour model. Many people find it more intuitive and so easier to use than RGB, particularly when adjusting colour using digital applications such as Adobe Creative Cloud.
HSB is one of a family of colour models that also includes HSV (hue, saturation, value) and HSI (hue, saturation, intensity).

Spectral colour model

The spectral colour model is neither an additive nor a subtractive colour model and is concerned instead with understanding the effects of refraction and dispersion on wavelengths of light and the way they separate into rainbow colours.

RYB colour model

RYB (red, yellow, blue) is a subtractive colour model. It is the standard colour model used for artist paints and when mixing opaque inks, dyes and pigments.