In this resource, a pure colour is a single unique spectral colour and so a fully saturated colour produced by a single wavelength of light.
In this resource, the vividness of a colour refers to its brightness. When a colour is at its most vivid then it is at maximum brightness (100%). As colours lose their brightness they appear progressively darker in tone until at minimum brightness they appear black (0%).
About an additive approach to colour
An additive approach to colour refers to a method of mixing different wavelengths of light to produce other colours.
An additive approach to colour is used to produce the vast array of hues an observer sees on the screens of TV’s, computers and phones.
Colour models that rely on an additive approach to colour include:
About additive colour and the RGB colour model
The RGB colour model used by TV, computer and phone screens involves additive colour mixing. The RGB colour model produces all the colours seen by an observer simply by combining the light emitted by arrays of red, green and blue pixels (picture elements) in different proportions.
- RGB colour is an additive colour model that combines wavelengths of light corresponding with red, green and blue primary colours to produce other colours.
- Red, green and blue are called additive primary colours in an RGB colour model because just these three component colours can produce any imaginable colour if mixed in the right proportion.
- Different colours are produced by varying the brightness of the component colours between fully off and fully on.
- When fully saturated red, green and blue primary colours are combined in equal amounts, they produce white.
- A fully saturated hue is produced by a single wavelength (or narrow band of wavelengths) of light.
- When any two fully saturated additive primary colours are combined, they produce a secondary colour: yellow, cyan or magenta.
- Some implementations of RGB colour models can produce millions of colours by varying the brightness of each of the three primary colours.
- The additive RGB colour model cannot be used for mixing pigments such as paints, inks, dyes or powders.
- The RGB colour model does not define the exact hue of the three primary colours so the choice of wavelengths for each primary colour is the principal determinant of their admixture.
- The RGB colour model can be made device-independent by specifying a colour profile such as sRGB or Adobe RGB (1998) which ensures consistent results regardless of the device used to output an image.
About amacrine cell functions
Amacrine cells are known to contribute to narrowly task-specific visual functions such as:
- Efficient transmission of high fidelity visual information with a good signal-to-noise ratio.
- Maintaining the circadian rhythm which keeps our lives tuned to the cycles of day and night and helps to govern our lives throughout the year.
- Measuring the difference between the response of specific photoreceptors compared with surrounding cells (centre-surround antagonism), so enabling edge detection and contrast enhancement.
- Motion detection and the ability to distinguish between the movement of things across the field of view and our own eye movements.
About amplitude, brightness, colour brightness and intensity
The terms amplitude, brightness, colour brightness and intensity are easily confused.
Amplitude
Brightness
- 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 the difference between the way a colour appears to an observer in well-lit conditions compared with 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:
- 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 measures the energy carried by a light wave or stream of photons:
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- 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.
- The intensity of light 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 centre-surround antagonism
Centre-surround antagonism refers to the way retinal neurons organize their receptive fields.
- Centre-surround antagonism refers to the way that light striking the human retina is processed by groups of light-sensitive cone cells.
- The centre component is primed to measure the sum-total of signals received from a small number of cone cells directly connected to a bipolar cell.
- The surround component is primed to measure the sum of signals received from a much larger number of cones around the centre point.
- The two signals are then compared to find the degree to which they disagree.
About colour models
A colour model is the how-to part of a 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.
A colour model is a way to:
- Make sense of colour in relation to human vision, to the world around us and to different media and technologies.
- Understand the relationship of colours to one another.
- Understand how to mix a particular colour from other colours to produce predictable results.
- Specify colours using names, codes, notation, equations etc.
- Organise and use colour for different purposes.
- Use colours in predictable and repeatable ways.
- Work out systems and rules for mixing and using different media (light, pigments, inks).
- Create colour palettes, gamuts and colour guides.
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:
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
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.
Distinct colour theories are evident in: