Spectral Colour & the RGB Colour Model
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This diagram shows six spectral colours, red, orange, yellow, green, blue and violet.
- Spectral colours are produced by a single wavelength of light.
- Some spectral colours can also be produced by mixing two wavelengths of light together.
Understanding the diagram:
- Above the line of coloured circles are the wavelengths of light that produce each spectral colour.
- Of the six colours (ROYGBV), red, green and blue can only be produced by a single wavelength of light.
- The other three spectral colours, orange, yellow and violet, can be produced either by a single wavelength of light or by additive mixing of pairs of primary colours.
- The bottom line of colours shows the proportions of red, green or blue used to produce orange, yellow and violet.
- The wavelength corresponding with each colour is shown in nanometres (nm). The wavelengths shown for each colour are for illustration only.
- In practice, the choice of wavelengths for primary colours usually depends on factors such as the colour model being used, the gamut of colours that a display device can produce and the context in which colours are to be viewed.
Description
Spectral Colour & the RGB Colour Model
TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
About the diagram
About the diagram
- This diagram shows six spectral colours – red, orange, yellow, green, blue and violet.
- Spectral colours are produced by a single wavelength of light.
- Some spectral colours can also be produced by mixing two wavelengths of light together.
Understanding the diagram
- Above the line of coloured circles are the wavelengths of light that produce each spectral colour.
- Of the six colours (ROYGBV), red, green and blue can only be produced by a single wavelength of light.
- The other three spectral colours, orange, yellow and violet, can be produced either by a single wavelength of light or by additive mixing of pairs of primary colours.
- The bottom line of colours shows the proportions of red, green or blue used to produce orange, yellow and violet.
- The wavelength corresponding with each colour is shown in nanometres (nm). The wavelengths shown for each colour are for illustration only.
- In practice, the choice of wavelengths for primary colours usually depends on factors such as the colour model being used, the gamut of colours that a display device can produce and the context in which colours are to be viewed.
Remember that:
- The bands of colour we see in rainbows correspond with the spectral colours red, orange, yellow, green, blue and violet.
- Spectral colours are produced naturally when light is refracted and dispersed by a prism or by rain.
- A spectral colour is produced by a single wavelength of light.
- The visible spectrum contains a continuum of spectral colours between red and violet.
- The visible spectrum is a small part of the electromagnetic spectrum.
- In a continuous spectrum, separate colours may be indistinguishable to the human eye.
- The fact that we see distinct bands of colour in a rainbow is an artefact of human colour vision.
Spectral and RGB colours
- Spectral colour should not be confused with RGB colour.
- Spectral colours are components of the visible spectrum.
- RGB colours are produced by mixing wavelengths of light corresponding with the three additive primary colours – red, green and blue.
- A diagram of spectral colour is usually presented in the form of a continuous linear spectrum organised by wavelength, so with red at one end and violet at the other.
- A diagram of RGB colour is often represented in the form of a colour wheel and shows the colours produced by mixing adjacent colours on the wheel.
Some key terms
Primary colours are a set of colours from which others can be produced by mixing (pigments, dyes etc.) or overlapping (coloured lights).
- The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet. It is the sensitivity of the eye to the electromagnetic spectrum that results in the perception of colour.
- A set of primary colours is a set of pigmented media or coloured lights that can be combined in varying amounts to produce a wide range of colours.
- This process of combining colours to produce other colours is used in applications intended to cause a human observer to experience a particular range of colours when represented by electronic displays and colour printing.
- Additive and subtractive models have been developed that predict how wavelengths of visible light, pigments and media interact.
- RGB colour is a technology used to reproduce colour in ways that match human perception.
- The primary colours used in a colour space such as CIELAB, NCS, Adobe RGB (1998) and sRGB are the result of an extensive investigation of the relationship between visible light and human colour vision.
The visible part of the electromagnetic spectrum is called the visible spectrum.
- The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.
- As light travels through the air it is invisible to our eyes.
- Human beings don’t see wavelengths of light, but they do see the spectral colours that correspond with each wavelength and colours produced when different wavelengths are combined.
- The visible spectrum includes all the spectral colours between red and violet and each is produced by a single wavelength.
- The visible spectrum is often divided into named colours, though any division of this kind is somewhat arbitrary.
- Traditional colours referred to in English include red, orange, yellow, green, blue, and violet.
ROYGBV are the initials for the sequence of colours that make up the visible spectrum: red, orange, yellow, green, blue, and violet.
- The visible spectrum refers to the range of colours visible to the human eye.
- White light, when passed through a prism, separates into a sequence of individual colours corresponding with ROYGBV which is the range of colours visible to the human eye.
- White light separates into ROYGBV because different wavelengths of light bend at slightly different angles as they enter and exit the prism.
- ROYGBV helps us remember the order of these spectral colours starting from the longest wavelength (red) to the shortest (violet).
- A rainbow spans the continuous range of spectral colours that make up the visible spectrum.
- The visible spectrum is the small band of wavelengths within the electromagnetic spectrum that corresponds with all the different colours we see in the world.
- The fact that we see the distinct bands of colour in a rainbow is an artefact of human colour vision.
A secondary colour is created by mixing two primary colours in equal parts within a particular colour model. The colour space can belong to either an additive colour model, which combines different light wavelengths, or a subtractive colour model, which mixes pigments or dyes.
- In additive colour models such as the RGB colour model, which deals with the effects of mixing coloured light, a secondary colour results from the overlap of the primary colours: red, green, and blue. The secondary colours produced by mixing pairs of primary colours in the RGB model are cyan, magenta, and yellow.
- In subtractive colour models such as the CMY colour model, which is concerned with mixing dyes and inks, a secondary colour results from the overlap of the primary colours: cyan, magenta, and yellow. The secondary colours produced by mixing pairs of primary colours in the CMY model are red, green, and blue.
The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.
- As light travels through the air it is invisible to our eyes.
- Human beings don’t see wavelengths of light, but they do see the spectral colours that correspond with each wavelength and colours produced when different wavelengths are combined.
- The visible spectrum includes all the spectral colours between red and violet and each is produced by a single wavelength.
- The visible spectrum is often divided into named colours, though any division of this kind is somewhat arbitrary.
- Traditional colours referred to in English include red, orange, yellow, green, blue, and violet.
A colour model is a system or framework used to understand, organise, and manipulate colour. It ranges from basic concepts, such as the sequence of colours in a rainbow, to more advanced models like RGB, CMYK, and CIE, which are essential for accurate colour reproduction in various fields, including digital media, printing, and manufacturing.
- A colour model, underpinned by colour theory, provides a precise and replicable approach to understanding:
- How the human eye perceives light and interprets colour.
- Different types of colour, including those produced by mixing lights, pigments, or inks.
- How to manage the diverse ways colour is processed by devices such as cameras, digital screens, and printers.
- Colour models enable us to:
- Make sense of colour in relation to human vision and the world around us.
- Use colours in logical, predictable, and replicable ways.
- Understand how to mix specific colours, whether using lights, pigments, inks, or dyes.
- Specify colours using names, codes, notations, or equations.
- Organise and apply colour for different purposes, from fabrics and interiors to vehicles.
- For more information see https://lightcolourvision.org/dictionary/definition/colour-model/
The spectral colour model represents the range of pure colours that correspond to specific wavelengths of visible light. These colours are called spectral colours because they are not created by mixing other colours but are produced by a single wavelength of light. This model is important because it directly reflects how human vision perceives light that comes from natural sources, like sunlight, which contains a range of wavelengths.
- The spectral colour model is typically represented as a continuous strip, with red at one end (longest wavelength) and violet at the other (shortest wavelength).
- Wavelengths and Colour Perception: In the spectral colour model, each wavelength corresponds to a distinct colour, ranging from red (with the longest wavelength, around 700 nanometres) to violet (with the shortest wavelength, around 400 nanometres). The human eye perceives these colours as pure because they are not the result of mixing other wavelengths.
- Pure Colours: Spectral colours are considered “pure” because they are made up of only one wavelength. This is in contrast to colours produced by mixing light (like in the RGB colour model) or pigments (in the CMY model), where a combination of wavelengths leads to different colours.
- Applications: The spectral colour model is useful in understanding natural light phenomena like rainbows, where each visible colour represents a different part of the light spectrum. It is also applied in fields like optics to describe how the eye responds to light in a precise, measurable way.
RGB colour is an additive colour model in which red, green and blue light is combined to reproduce a wide range of other colours.
- The primary colours in the RGB colour model are red, green and blue.
- In the RGB model, different combinations and intensities of red, green, and blue light are mixed to create various colours. When these three colours are combined at full intensity, they produce white light.
- Additive colour models are concerned with mixing light, not dyes, inks or pigments (these rely on subtractive colour models such as the RYB colour model and the CMY colour model).
- The RGB colour model works in practice by asking three questions of any colour: how red is it (R), how green is it (G), and how blue is it (B).
- The RGB model is popular because it can easily produce a comprehensive palette of 1530 vivid hues simply by adjusting the combination and amount of each of the three primaries it contains.
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