Dictionary Pods Tag: Colour brightness

Amplitude, brightness, colour brightness & intensity

About amplitude, brightness, colour brightness and intensity

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

Amplitude
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:
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.

Colour brightness

About colour brightness
  • In this resource, the term colour brightness is used to describe how things appear to a human observer in terms of their perception of colour.
  • Colour is what humans perceive in the presence of radiated or reflected light.
  • The brightness of the colour of an object or surface (colour brightness) depends on the wavelengths and intensity of light that illuminate it and the amount of light it reflects.
  • The colour brightness of a transparent or translucent medium may be influenced by the wavelengths and intensity of light that pass through or reflect off it and the amount it transmits or reflects.
  • Colour brightness is frequently influenced by the contrast between how a colour appears to an observer under well-lit conditions and its more subdued appearance when in shadow or under poor illumination.
  • The perception of colour brightness is also influenced by hue, as certain hues appear brighter than others to human observers. For example, a fully saturated yellow may appear relatively brighter than a fully saturated red or blue.

Colour brightness & light intensity

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.

HSB colour model & colour brightness

About the HSB colour model and colour brightness

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

  • The RGB and HSB colour models differ only in the way colours are represented in terms of colour notation and handled in software and applications.
  • Both the HSB and RGB colour models involve mixing red, green, and blue light to produce other colours.
  • HSB is popular because it offers an intuitive method for selecting and adjusting colours within applications like Adobe Creative Cloud, which is commonly used in design, photography, and web development.
  • The HSB colour model can be used to describe any colour on a TV, computer or phone screen.

In the HSB colour model:

  • Hue refers to the perceived difference between one colour and another and accounts for colour names such as red, yellow, green or blue.
    • Hue can be measured as a location on a colour wheel and expressed in degrees between 00 and 2590.
  • Saturation refers to the perceived difference between one colour and another in terms of purity.
    • Saturation is measured between a fully saturated colour (100%) and an unsaturated colour that appears dull and washed out, eventually reaching a monochromatic grey tone (0%).
    • A fully saturated colour is produced by a single wavelength or a narrow band of wavelengths of light.
    • On HSB colour wheels, saturation is typically shown to increase from the centre to the circumference.
  • Brightness (colour brightness) refers to the difference between a hue that appears bold and vivid at maximum brightness (100%) and then appears progressively darker in tone until it appears black at minimum brightness(0%).
  • Colour brightness is often evident in the distinction between how a colour appears to an observer under well-lit conditions compared to its more subdued appearance when in shadow or under poor illumination.