Brightness: HSB colour model

About colour models

A colour model derived from colour theory enables a more precise and reproducible method of representing and working with colour.

• Colour models are a practical application of colour theory that establish terms, definitions, rules or conventions, and systems of notation for encoding colours and their relationships to one another.
• These days, the most practical colour models are built into applications such as Adobe Creative Cloud and allow seamless digital output to TVs, computers, phones, or printing onto paper and other surfaces.
• Understanding colour models and utilizing them effectively can contribute to maintaining consistent and accurate colour reproduction across various media.
• Widely used colour models include:
  • Spectral colour model.
  • RGB colour model.
  • HSB colour model.
  • CMYK colour model.
• In addition to the colour models mentioned above, numerous other models are used in specific contexts, such as the Lab colour model employed in printing or the LCH colour model used in digital image processing.

A colour model is a framework that allows us to:

• Make sense of colour in relation to human vision, the surrounding world, and various media and technologies.
• Understand the relationship between different colours and their properties.
• Mix specific colours from other colours to achieve predictable and desired results.
• Specify colours using names, codes, notations, equations, and other forms of representation.
• Organise and utilize colour for different purposes, such as design, visual arts, or scientific applications.
• Use colours in consistent and repeatable ways across different platforms and media.
• Develop systems and rules for blending and using different media, such as light, pigments, or inks.
• Create colour palettes, define gamuts, and establish colour guides to guide artistic or design decisions.

About brightness & colour models

• The term brightness is often used in association with a specific colour model.
• Examples of colour models include:
  • HSB colour model
  • Spectral colour model
  • RGB colour model
  • CMYK colour model
• The HSB colour model uses the term brightness alongside hue and saturation.
• Some colour models don’t use the term brightness at all, so when we change from one colour model to another it’s best to change our terminology as well.

About colour theory

Colour theories underpin colour management by seeking to explain how human beings perceive colour and establish the rational basis for practical how-to methods for managing colour in different situations.

A system of colour management may be associated with:

• • A colour theory
  • A colour model
  • Colour notation
  • A colour space
  • Colour wheel/s, colour picker/s
  • Colour swatch/es, colour sample/s
  • Colour profile/s for digital workspaces, monitors, printers etc.

Colour theory and human perception

The aspect of colour theory concerned with the human perception of colour aims to answer questions about:

• How our eyes register colour when exposed to light.
• The way our eyes and brains work together to produce the complex colour perceptions that make up the visible world.
• The part of the electromagnetic spectrum that is related to colour and how our eyes respond to different wavelengths of light.
• The fact that red, green and blue lights combined in different proportions can produce the impression of all the colours of the visible spectrum.
• The way colours appear in different situations such as in low or bright light and under artificial lighting.
• Human responses to different combinations of colour such as analogous, complementary and contrasting colours.
• The differences between the scientific, technical and creative understandings and descriptions of colour.
• Understanding the differences between:
  • The way our eyes see colour
  • Light and colour in the world around us
  • The colour of opaque objects and surfaces
  • The colour of transparent media
  • Colour on TVs, computers and phone screens
  • Colour in printed images

Colour theory and colour management

The aspect of colour theory concerned with how-to methods for managing colour in different situations aims to answer questions about:

• The differences between mixing coloured lights, pigment or inks.
• Mixing and managing ranges (gamuts) of colours in logical, predictable and repeatable ways.
• Identifying and mixing particular colours in predictable and repeatable ways.
• Specifying colours using names, codes, notation, equations etc.
• The difference between additive and subtractive colour mixing.
• Systems and rules for mixing different and applying them to different materials such as fabrics, interiors and vehicles.
• Creating colour palettes, gamuts and colour guides.
• Managing the consistent reproduction of digital colour from start to finish.

Where to find colour theories

• Trichromatic colour theory
• Opponent colour theory
• Neurological research
• Subtractive and additive theories of colour
• The Munsell colour system
• LAB colour model
• Spectral colour model
• RGB colour model
• HSB colour model
• CMY colour model
• Pantone Matching System (PMS) is a standardised system for the colour printing industry.
• RAL classic colour system is used mainly for powder coating, varnish, and plastic colouring.

About the HSB colour model

The HSB colour model is an additive colour model used to mix light (subtractive colour models are used to mix pigments and inks).

• The main difference between the HSB colour model and the RGB colour model is how colours are represented and managed in software and applications.
• The HSB model represents colours based on hue, saturation, and brightness, whereas the RGB model mixes red, green, and blue light to create colours.
• HSB is popular because it provides a user-friendly way to select and modify colours when using applications like Adobe Creative Cloud for design, photography, or web development.
• On HSB colour wheels, saturation typically increases from the centre towards the edge.

In the HSB colour model:

• Hue refers to the perceived difference between colours and is usually described using names such as red, yellow, green, or blue.
  • Hue can be measured as a location on an HSB colour wheel and expressed as a degree between 0 and 360.
• Saturation refers to the vividness of a colour compared to an unsaturated colour.
  • Saturation is measured between a fully saturated colour (100%) and an unsaturated colour (0%)that appear either:
    • Dull and washed out until all colour disappears, leaving only a monochromatic grey tone (0%).
    • Misty or milky the nearer they are to white.
  • On many HSB colour wheels, saturation decreases from the edge to the centre.
• Brightness refers to the perceived difference in the appearance of colours under ideal sunlit conditions compared to poor lighting conditions where a hue’s vitality is lost.
  • Brightness can be measured as a percentage from 100% to 0%.
  • As the brightness of a fully saturated hue decreases, it appears progressively darker and achromatic.

About amplitude, brightness, colour brightness and intensity

The terms amplitude, brightness, colour brightness and intensity are easily confused. In this resource:

Amplitude

• Amplitude refers to the amount of energy carried by an electromagnetic wave. The higher the amplitude, the more energy the wave carries.
• Amplitude is a feature of electromagnetic waves.
• Other features include:
  • Centreline
  • Crest
  • Frequency
  • Oscillation
  • Trough
  • Velocity
  • Wavelength
  • Wave-cycle

Brightness

• Brightness refers to a property of light, to how strong a light source or light reflected off an object appears to be.
• Brightness is related to how things appear from the point of view of an observer.
  • When something appears bright it seems to radiate or reflect more light or colour than something else.
  • Brightness may refer to a light source, an object, a surface, transparent or translucent medium.
  • The brightness of light depends on the intensity or the amount of light an object emits( eg. the Sun or a lightbulb).
  • The brightness of the colour of an object or surface depends on the intensity of light that falls on it and the amount it reflects.
  • The brightness of the colour of a transparent or translucent medium depends on the intensity of light that falls on it and the amount it transmits.
  • Because brightness is related to intensity, it is related to the amplitude of electromagnetic waves.
  • Brightness is influenced by the way the human eye responds to the colours associated with different wavelengths of light. For example, yellow appears relatively brighter than reds or blues to an observer.

Colour Brightness

•  Colour brightness refers to how colours appear to a human observer in terms of the lightness or darkness of colours.

So colour brightness can refer to the difference between how a colour appears to an observer in well-lit conditions and its subdued appearance when in shadow or when poorly illuminated.

• In a general sense, brightness is an attribute of visual perception and produces the impression that something is radiating or reflecting light and/or colour.
• Colour brightness increases as lighting conditions improve, whilst the vitality of colours decreases when a surface is poorly lit.
• Optical factors affecting colour brightness include:
  • The angle at which incidence light approaches a medium, object or surface
  • The composition of incident light in terms of wavelength and frequency
  • The polarization of incident light
• Material properties affecting the colour brightness of a medium, object or surface include:
  • Chemical composition
  • Three-dimensional form
  • Texture
  • Reflectance
• Perceptual factors affecting colour brightness include:
  • Adjacent colours: The presence and illumination of adjacent colours can affect both the apparent hue and brightness of a target colour.
  • Attributes of visual perception.

Intensity

• • Intensity refers to the amount of light produced by a light source or the amount of light that falls on a particular area of the object.
  • So intensity measures the energy carried by a light wave or stream of photons:
    • When light is modelled as a wave, intensity is directly related to amplitude.
    • When light is modelled as a particle, intensity is directly related to the number of photons present at any given point in time.
    • Light intensity falls exponentially as the distance from a point light source increases.
    • Light intensity at any given distance from a light source is directly related to its power per unit area (when the area is measured on a plane perpendicular to the direction of propagation of light).
    • The power of a light source describes the rate at which light energy is emitted and is measured in watts.
    • The intensity of light is measured in watts per square meter (W/m2).
    • Cameras use a light meter to measure the light intensity within an environment or reflected off a surface.

About colour brightness & light intensity

• The perception of colour depends on the wavelengths that reach an observer’s eyes. Red has a longer wavelength, while violet has a shorter wavelength.
• Any colour (e.g. red, magenta, or violet) can be defined by its hue, saturation, and brightness.
• Saturated colours are produced by a single wavelength of light or a narrow band of wavelengths.
• The brightness of a colour depends on the intensity of the light emitted by a light source (e.g., a coloured light bulb) and the amount of light reflected from a coloured surface.
  • So, for example, the texture of a surface can affect brightness even when the intensity of the light source remains constant.
• The intensity of light, along with factors such as phase and interference, are directly related to the amplitude of an electromagnetic wave.
• Amplitude measures the height of light waves from the centre-line of a waveform to its crest or to a corresponding trough.
• Colour brightness, light intensity, and the amplitude of a light wave can all be thought of in terms of the number of photons that strike the eye of an observer.
  • Therefore, increasing the amplitude of a wavelength of light will increase the number of photons falling on an object, making it appear brighter to an observer.