Dictionary tag: C

• A colour space defines the range of colours available for an artist, designer, or technician to work with. It can be broad, encompassing a wide spectrum of colours, or narrow, limiting the palette to a specific set. The underlying colour theory and model used in a workflow partially determine the colour space.
• Colour spaces are essential for colour management, especially when working across devices in a digital environment. They help ensure consistent colour reproduction across screens and printers. To match a specific device like a projector or printer, you can specify its type and model during the editing process.
• When the intended output device is uncertain, adding a colour profile like sRGB or Adobe RGB to a digital file can help guarantee accurate colour reproduction. A colour profile is essentially a set of instructions that tells a device how to interpret and process colour information, ensuring the final output matches the original intent.

Perceptual colour space

• A perceptually based colour space can encompass all the colours visible to a person with average eyesight or can be limited, for example, to colours that are monochrome, analogous, complementary or contrast with one another.
• Perceptually based colour spaces can be based on informal subjective preferences or based on rigorous scientific and mathematical methodologies as is the case with:
  • LMS colour space – One of the first systematic demonstrations of tristimulus colour theory.
  • CIE 1931 XYZ – based on measurements of human colour perception and the basis for almost all subsequent colour spaces.
  • The CIE xy chromaticity diagram – an implementation of the CIE 1931 XYZ colour space.
  • CIELUV 1976 –  a modification of CIE 1931 XYZ used to display additive mixtures of light more conveniently.
  • CIELAB 1976 – commonly used for surface colours, but not for mixtures of light.
• CIE refers to the International Commission on Illumination.
• Whilst RGB colour spaces use red, green and blue as primary colours and CMYK use cyan, magenta and yellow, purely perceptually based colour spaces associated with the trichromatic colour model such as the LMS colour space.

Artist’s colour space

• When an artist chooses a limited number of tubes of oil paint to add to a palette they have committed themselves to a colour space aligned with the RYB subtractive colour model and each selected colour helps to define the colour space they plan to work within.

Digital colour space

• When a designer using the Adobe Creative Clouds apps such as Illustrator is selecting a colour space when they choose the RGB, HSB, CMYK or greyscale colour model from the Colour Panel.
• Selections made in the Colour Panel of Adobe apps are often referred to as intermediate colour spaces, used during the editing of images but not part of end-to-end colour management.
• When an additive or subtractive colour model is selected for a workflow then a choice is made between an additive or subtractive colour space.
• The choice of swatch library and harmony rules can add further definition to the colour space chosen for a particular project or workflow.
• A digital colour space can be device dependent or be part of an end-to-end and device-independent system of colour management.

Examples of colour models used for device-dependent intermediate colour spaces

• • RGB colour model
  • HSB colour model
  • CMY colour model
  • Greyscale colour model
  • These are device-dependent colour spaces because the way colours appear and are reproduced depends on the capabilities and set-up of other independent devices.

Examples of device-independent colour spaces

• • • sRGB
    • Adobe RGB (1998)
    • CIE (1931) XYZ colour space
    • Prophoto RGB
      • Every colour model has its own system of notation used to identify colours in a human and machine-readable form.
      • Examples of colour notation include:
        • RGB colour values
        • HSB colour values
        • CMYK colour values
        • LMS tristimulus values

Colour space diagrams

• Colour spaces are conceptual tools that conceive of colour as partially or completely filling a physical space.
• Think of a colour space as a room in which colours have been carefully stored and ordered.
• Colour spaces are often represented (modelled or mapped) in diagrams using graphs with two, three or four axes.
  • The axes of the RGB colour space correspond with the three primary colours, red, green and blue.
  • The axes of the HSB colour space correspond with hue, saturation and brightness.
  • The axes of the CMYK colour space correspond with cyan, magenta, yellow and black.
  • The axes of a trichromatic CIE 1931 XYZ colour space correspond with XYZ tristimulus colour values.
  • The axes of a trichromatic LMS colour space correspond with LMS tristimulus colour values.
  • The axes of the CIE 1931 xy chromaticity diagram map hue and saturation whilst excluding brightness.
• Colour spaces can be presented as tables of data or visualized as:
  • 3D shapes such as cones, cubes, cylinders and stacked disks
  • 3D volumes that appear to be solid objects
  • 2D colour wheels, grids or chromaticity diagrams.

Colour theories discussed here at lightcolourvision.org include:

• CMY colour model
• Greyscale colour model
• HSB colour model
• Lab colour model
• RGB colour model
• Spectral colour model
• Trichromatic colour model

Other important references include:

• Munsell colour system – a standardized and perceptually uniform colour model that defines colours based on their hue, value (lightness), and chroma (colour purity).
• Pantone Colour Matching System (PMS) – a standardised system for the colour printing industry.
• RAL colour space system – used mainly for powder coating, varnish, and plastic colouring.

Colour theories underpin:

• Colour management
• Colour model/s
• Colour space/s
• Colour wheel/s, colour picker/s, colour swatches
• Colour profile/s for digital workspaces, monitors, printers etc.

Human perception of colour

The aspect of colour theory concerned with human perception 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 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

How-to methods for managing colour

The aspect of colour theory concerned with how-to methods for working with 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 media and applying them to fabrics, interiors and vehicles.
• Creating colour palettes, gamuts and colour guides.
• Managing the consistent reproduction of digital colour from start to finish.

Contributors to contemporary theories of colour

Some important contributors to contemporary theories of colour include:

• Leone Battista Alberti (c. 1435)
• Leonardo da Vinci (c. 1490)
• Isaac Newton: Opticks (1704)
• Johann Wolfgang von Goethe: Theory of Colours (1810)
• Michel Eugène Chevreul: The Law of Simultaneous Color Contrast (1839)
• Charles Hayter:  A New Practical Treatise on the Three Primitive Colours Assumed as a Perfect System of Rudimentary Information (1826)
• Ogden Rood: Modern Chromatics (1879)
• Albert Henry Munsell:  Book of Colour (1915)
• Wilhelm Ostwald: Colour Atlas (1919)
• The Bauhaus: including  Johannes Itten,  Wassily Kandinsky, Paul Klee and Joseph Albers (1919 – 1933)

RGB colour model

The RGB colour model uses both decimal and hexadecimal triplets for colour notation. Each of the three components within a triplet contains a value corresponding to red, green or blue. The colour values within RGB triplets appear as follows:

• The colour values in decimal notation for orange: R=255, G=128, B=0.
• The colour value in hexadecimal RGB notation for orange: #FF8000.

HSB colour model

The HSB colour model uses decimal triplets for colour notation. Each of the three components within a triplet contains a value corresponding to hue, saturation or brightness. The colour values within HSB triplets appear as follows:

• The colour values in decimal notation for orange: H=30.12, S=100, B=100.

CMYK colour model

The CMYK colour model uses decimal quadruplets for colour notation. Each of the four components within a quadruplet contains a value corresponding to cyan, magenta, yellow or black. The colour values within CMYK quadruplets appear as follows:

• The colour values in decimal notation for orange: C=0, M=61.48, Y=100, K=0.

RGB colour values

RGB colour values are expressed as decimal triplets (yellow = 255, 255, 0) or hexadecimal triplets (green = #00FF00). Computer software is programmed to recognise RGB colour values.

In both cases, the triplets determine the amount of red, green and blue used to produce a specific colour.
A decimal triplet comprises three numbers between 0 and 255 divided by commas.
A hexadecimal triplet starts with a # sign followed by three two-digit numbers with values between  00 and FF written without spaces between.

RGB colour values are based on decimal notation (triplets with a base 10) or hexadecimal notation (triplets with a base 16).

• Decimal notation uses 10 digits from 0 to 9: 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.
• The hexadecimal notation uses 16 digits from 0 to F: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E and F.
• Hexadecimal notation for values between 16 and 31 are 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1A, 1B, 1C, 1D, 1E and 1F.

RGB decimal values

• In decimal notation, an RGB triplet represents the values of red, green, then blue. A range of decimal numbers between 0 to 255 can be selected for each value.
  • Red = 255, 0, 0
  • Yellow = 255, 255, 0
  • Green = 0, 255, 0
  • Cyan = 0, 255, 255
  • Blue = 0, 0, 255
  • Magenta = 255, 0, 255

RGB hexadecimal values

• In hexadecimal notation, an RGB triplet represents the value of red, green, then blue. A range of hexadecimal numbers from 00 to FF can be selected for each value.
• The hash symbol (#) is used to indicate hex notation.
  • Red = #FF0000
  • Yellow = #FFFF00
  • Green = #00FF00
  • Cyan = #00FFFF
  • Blue = #0000FF
  • Magenta = #FF00FF

• Colour is not a property of electromagnetic radiation, but a feature of visual perception.
• The human eye, and so human perception, is tuned to the range of wavelengths of light that make up the visible spectrum and so to the corresponding spectral colours between red and violet.
• Light, however, is rarely of a single wavelength, so an observer will usually be exposed to a spread of different wavelengths of light or a mixture of wavelengths from different areas of the spectrum.
• An observer’s perception of colour is a subjective process as the eyes and brain respond together to stimuli produced when incoming light reacts with light-sensitive cells within the retina at the back of the eye.
• The perception of colour can be influenced by various factors, such as lighting conditions, surrounding colours, and individual differences in colour perception.

• A colour wheel is a perceptual tool used to explore a colour model.
• Colour models that use colour wheels include:
  • RGB colour model – Used for mixing light.
  • RYB colour model – Used for mixing opaque pigments
  • CMY colour model – Used for mixing semi-transparent inks.
• Colour wheels are not used to explore the spectral colour model because each colour corresponds with a single wavelength of light rather than mixtures of primary colours.
• The spectral colour model is usually portrayed as a strip of colours with red at one end and violet at the other.

• The minimum number of segments in a colour wheel is three with a primary colour in each.
• Segments between primary colours are used to explore the result of mixing adjacent pairs of primary colours to produce secondary colours.
• Segments between secondary colours can be used to explore the result of mixing further pairs of adjacent colours.
• Wheels of increasing complexity are produced by further subdivisions.

• The colours produced between the primary colours in a colour wheel are called secondary colours.
• The colours produced between the secondary colours are called tertiary colours.
• Colour wheels used to explore additive and subtractive colour models start with different sets of primary colours.
  • An RGB colour wheel, used to explore additive mixing of light, starts with red, green and blue primary colours.
  • An RYB colour wheel, used to explore subtractive mixing of pigments starts with red, yellow and blue primary colours.
  • A CMY colour wheel, used to explore subtractive mixing of printing inks starts with cyan, magenta and yellow primary colours.

• Pairs of complementary colours always involve one primary colour and a secondary colour that are opposite one another on a colour wheel. The secondary colour on an RGB colour wheel or HSB colour wheel can always be produced by mixing the other two of the three primaries.
• Complementary colours always juxtapose one cool colour with a warm colour. Reds, oranges and yellows are the warm colours, while blues, greens, and purples are the cool colours.
• In the context of light, complementary colours result from the additive mixing of wavelengths of light. When all three primary colours are mixed they produce white.
• In the context of paints and inks, complementary colours result from the subtractive colour mixing of pigments. When all three primary colours are mixed they produce black.
• The mixing of pigments such as powder colours is more complex than mixing known wavelengths of light. When all three primary colours (cyan/magenta/yellow inks or red/yellow/blue powder colours) are mixed they often produce muddy brown or purple colours.

• A compound (chemical compound) is formed when different elements react, forming bonds between their atoms.
• A molecule is the smallest indivisible unit of a compound that retains its chemical properties.
• Different elements react and form bonds between their atoms to create a compound.
• Compounds have unique properties that are different from the properties of their constituent elements.
• Introducing a new element to a compound can lead to additional reactions and the formation of new compounds.

• Compounds can be categorized into four types based on the type of bonding between constituent atoms:
  • Compounds held together by covalent bonds form molecules.
  • Ionic compounds are formed by the attraction between positively and negatively charged ions.
  • Intermetallic compounds are held together by metallic bonding between metal atoms.
  • Complexes are formed through coordinate covalent bonds between a central atom and ligands.

• Compounds are one type of substance encountered in chemistry. Other types of substances include:
  • Mixtures: A substance consisting of two or more different substances that are physically combined.
  • Solutions: A homogeneous mixture where one or more substances (solutes) are dissolved in another substance (solvent).
  • Alloys: A homogeneous mixture of two or more metals, or a metal with a non-metal.
  • Colloids: A mixture where particles of one substance are dispersed throughout another substance but do not settle out or dissolve.
  • Isotopes: Different forms of an element with the same number of protons but different numbers of neutrons in their nuclei.

• Concept maps help to visually organize knowledge, making it easier to understand complex topics by showing how ideas are related. They are often used in education, research, and planning to:
  • Clarify relationships: Concept maps show how different ideas connect, helping people to understand connections between concepts that might not be immediately obvious.
  • Simplify complex subjects: By breaking down large topics into smaller, manageable parts, concept maps help people grasp complicated subjects more easily.
  • Facilitate learning and memory: Visually representing information helps learners see the big picture, making it easier to recall and understand the relationships between ideas.
  • Encourage critical thinking: Building a concept map involves analyzing and organizing information, which promotes deeper thinking and understanding.
• In practice, a concept map might start with a central idea (like “light and colour”) and branch out to related subtopics, each with its own linked concepts (e.g., “visible spectrum,” “wavelengths,” “perception”).