Colour models are 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.
These days, the most practical colour models are built into applications such as Adobe Creative Cloud which allow easy digital output to TV’s, computers and phones or printing onto paper and other surfaces.
A colour model is a way of:
- Making sense of colour in relation to human vision, to the world around us and to different media and technologies.
- Understanding the relationship of colours to one another.
- Understanding how to mix a particular 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 colour media.
- 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
- 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.
- 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 models, 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.
Three models used by graphic designers on a day to day basis are the additive RGB and HSB models on their computers and the CMYK model for digital printing.
- Seeing colour results from how our eyes respond to light.
- In the real world, colours are changing all the time, appear differently in different situations and are infinitely variable.
- So colour models help us mediate our relationships with the world.
Spectral 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 include a fourth component, black ink (K), to increase the density of darker colours and blacks.
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 inks, dyes and pigments.
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 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
- A colour model is 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 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 system considers all the factors that affect how an image appears including the colour theory/model, how information is encoded before sending to an output device, the circumstances in which it is viewed and factors that affect observation.