Chemical bond

chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds.

  • A chemical compound consists of two or more atoms from different elements chemically bonded together.
  • There are two types of chemical bond: covalent bonds and ionic bonds:
    • A covalent bond forms when two atoms share a pair of electrons.
    • Atoms can lose or gain electrons in chemical reactions. When they do this they form charged particles called ions.
  • Chemical bonds occur because opposite charges attract via the electromagnetic force.
  • Negatively charged electrons orbiting the nucleus of an atom and the positively charged protons in the nucleus attract each other.
  • An electron positioned between two nuclei will be attracted to both of them, and the nuclei will be attracted toward electrons in this position. This attraction constitutes the chemical bond.
  • Due to the matter-wave nature of electrons and their smaller mass, they must occupy a much larger amount of volume compared with the nuclei, and this volume occupied by the electrons keeps the atomic nuclei in a bond relatively far apart, as compared with the size of the nuclei themselves.
  • The physical world is held together by chemical bonds, which dictate the structure and the bulk properties of matter.

https://en.wikipedia.org/wiki/Chemical_bond

Chromophore

The chromophore is the part of a molecule responsible for its colour.

  • Things appear to have colour because they absorb some wavelengths of light and reflect others.
  • The chromophore is the region of a molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum.
  • A  molecular orbital describes the location and wave-like behaviour of an electron in a molecule.
  • Visible light that hits the chromophore can be absorbed by exciting an electron from its ground state into an excited state.

https://en.wikipedia.org/wiki/Chromophore

Colour

Things appear coloured to an observer because colour corresponds with a property of light that is visible to the human eye. The visual experience of colour is associated with words such as red, blue, yellow, etc.

Colour

Things appear coloured to an observer because colour corresponds with a property of light that is visible to the human eye. The visual experience of colour is associated with words such as red, blue, yellow, etc.

Why we see colour
Light and colour
  • Light is electromagnetic radiation (radiant energy), which, detached from its source, is transported by electromagnetic waves (or their quanta, photons) and propagates through space. Even if humans had never evolved, electromagnetic radiation would have been emitted by stars since the formation of the first galaxies over 13 billion years ago.
  • The experience of colour is a feature of human vision that depends first of all on the construction of our eyes and the wavelength, frequency and brightness of visible light that strikes the retina at the back of each eye.
  • Because colour is a visual experience that is specific to each and every one of us at any given moment, we share our experiences of colour using language but to make sure we are talking about the same colour we use examples.
White light
  • The name given to light that contains all wavelengths of the visible spectrum at equal intensity is white light.
  • The term white light doesn’t mean light is white as it travels through the air. As light travels through the air it is invisible to our eyes.
  • When white light strikes a neutral coloured object, and all wavelengths are reflected, then it appears white to an observer.
Observation of colour
  • 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 this small part of the electromagnetic spectrum that results in the perception of colour.
  • The colour an observer sees depends on:
    • The wavelengths of visible light emitted by a light source.
    • The wavelengths transmitted through a medium or reflected off an object.
  • Although a human observer can distinguish between many thousands of wavelengths of light in the visible spectrum our brains often produce the impression of bands of colour.
  • As light travels from one medium to another, such as from air to glass, the wavelength changes but the frequency remains the same so the colour seen by an observer remains the same.
References
  • https://en.wikipedia.org/wiki/Color

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.

About colour brightness
  • In a general sense, brightness is an attribute of visual perception in which something appears to an observer to be radiating or reflecting light.
  • 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 colour brightness of a medium, object or surface include:
    • Chemical composition
    • Three dimensional form
    • Texture
    • Reflectance
  • Perceptual factors affecting colour brightness include:
About brightness
Colour theory
  • When an observer asks themselves about the colour of something, they will often unconsciously think in terms of a particular colour theory associated with:
    • Spectral colours with names associated with atmospheric rainbows
    • Pigments, where powders are mixed with water, oil or acrylic to produce different colours
    • Objects and surfaces which transmit, reflect and absorb wavelengths of light in different proportions
  • A broader vocabulary of names can be used to describe colours such as dark red, vermilion, golden yellow, lemon yellow, pale yellow, greenish-yellow, chartreuse, leaf green or light green.
  • A colour model derived from a theory of colour allows for a more exact and reproducible approach to colour.
Brightness, Intensity, amplitude

In this dictionary:

  • Brightness is used in connection with the perception of colour.
  • Intensity is used in connection with the amount of light that is produced by or falls on an object.
  • Amplitude is used in connection with the properties of electromagnetic waves.
Colour brightness and light intensity
  • The perception of colour in the world around us depends on the spread of wavelengths that reach the eyes of an observer.
  • The perception of brightness of a colour depends on the amount of light an object emits, absorbs or reflects.
  • The perception of  brightness depends on the amplitude of the oscillation of light waves. Amplitude is a measure of the height of light waves from trough to peak.
  • The amplitude of a light wave or the intensity of light can be thought of in terms of the volume of photons that it carries.
  • Increase the amplitude of a wavelength of light and the volume of photons falling on an object will increase its apparent brightness to an observer.
References

Colour constancy

Colour constancy refers to the ability of the human eye and brain to automatically compensate when objects change colour because of changes in illumination.

  • Colour vision relies on colour constancy to enable an observer to perceive the colour of an object as almost unchanged as levels of illumination change and the spectral distributions of light changes.
  • A human observer will often not notice when the colour of object changes as the source of illumination changes e.g. sunlight to artificial light.
  • Colour vision allows us to distinguish different objects by their colour. In order to do so, colour constancy can keep the perceived colour of an object relatively unchanged when the illumination changes among various broad (whitish) spectral distributions of light.
  • Colour constancy is achieved by chromatic adaptation. The International Commission on Illumination defines white (adapted) as “a colour stimulus that an observer who is [chromatically] adapted to the viewing environment would judge to be perfectly achromatic and to have a luminance factor of unity. The colour stimulus that is considered to be the adapted white may be different at different locations within a scene.
  • The effect of changes in colour balance is very noticeable when comparing photographs of the same subject taken in different lighting conditions. Cameras use white balance to compensate for changes in illumination.

https://en.wikipedia.org/wiki/Color_constancy

Colour model

A colour model is a mathematical system used to describe colours using a set of numeric values.

A colour model is a way of:

  • Making sense of the colours we see around us in the world.
  • Understanding the relationship of colours to one another.
  • Understanding how to mix each type of coloured media to produce predictable results.
  • Specifying colours using names, codes, notation, equations etc.
  • Organising and using colours for different purposes.
  • Using colours in predictable and repeatable ways.
  • Working out systems and rules for mixing and using different types of colour.
  • Creating colour palettes, gamuts and colour guides.

Colour model

Colour models are the how-to part of 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.

These days, the most practical colour models are built into applications such as Adobe Creative Cloud which allow easy digital output to TV’s, computers and phones or printing onto paper and other surfaces.

About colour models?

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 colours for different purposes.
  • Use colours in predictable and repeatable ways.
  • Work out systems and rules for mixing and using different media (light, powders, inks).
  • Create colour palettes, gamuts and colour guides.
Why use colour models?
  • Colour models help to relate colours to:
    • One another
    • Light sources, objects and materials
    • Perceptions and experiences.
  • Colour models make sense of the fact that coloured lights, transparent inks and opaque paints (etc.) all produce different results when mixed.
  • Colour models help us manage the fact that colours mean and feel different and have different associations depending on context.
  • Colours models help us manage the fact that colours behave and appear differently:
    • When emitted by different types of light source.
    • When applied to, mixed with, or projected onto different materials.
    • When used for different purposes (fabrics, electrical wiring and components, print media, movies etc.)
    • When seen or used in different situations (indoors, in sunlight, in low light, on a digital display etc.)
Additive and subtractive colour

There are two principal types of colour models, additive and subtractive. Additive colour models are used when mixing light to produce colour. Subtractive colour models are used for printing with inks and dyes.

Three models used by graphic designers on a day to day basis are the additive RGB and HSB models on their computers and the CMYK model for digital printing.

Remember that:

  • Seeing colour results from how our eyes respond to light.
  • In the real world, colours are changing all the time, appear differently in different situations and are infinitely variable.
  • So colour models help us mediate our relationships with the world.
Spectral colour model

The spectral colour model is an additive colour associated with rainbows and the refraction and dispersion of wavelengths of light into bands of colour.

RGB colour model

RGB (red, green, blue) is an additive colour model based on the trichromatic theory of colour vision. It is widely used in video cameras, for producing colour on digital screens and with software such as Adobe Creative Cloud.

CMY(K) colour model

CMY (cyan, magenta, yellow) is a subtractive colour model. It is the standard colour model for digital printing. Printers include a fourth component, black ink (K), to increase the density of darker colours and blacks.

RYB colour model

RYB (red, yellow, blue) is a subtractive colour model. It is the standard colour model used for artist paints and when mixing inks, dyes and pigments.

HSB colour model

HSB (hue, saturation, brightness) is a popular additive colour model. Many people find it more intuitive and so easier to use than RGB, particularly when adjusting colour using digital applications such as Adobe Creative Cloud.

HSB is one of a family that also includes HSV (hue, saturation, value) and HSI (hue, saturation, intensity).

Applications of colour models

Colour models have many applications including:

  • Understanding colour vision.
  • Mixing different coloured media eg. lights, paints, inks and dye.
  • Using colour with different equipment and technologies.
  • Storing and sharing colour information eg. notation systems and file types.
  • Describing and naming colours in a consistent way.
  • Nomenclature for describing similar things eg. systems for describing birds according to their colour.
  • Comparing colours eg. swatches and samples.
Colour models, colour spaces and colour systems
  • A colour model is device-dependent. This means that a colour specified as R=220, G=180, B=140 might appear differently on two digital monitors or when printed by different printers with the same specifications. In other words, the exact colour produced depends on the device that produces it not on the colour model itself.
  • A colour space describes the range of colours that an observer might see. Colour spaces can be very limited when a photo is printed on a low price digital printer, large when the same image is viewed on a high definition digital display , or huge when the original scene is viewed in bright sunlight on a summer day.
  • A colour system considers all the factors that affect how an image appears including the colour theory/model, how information is encoded before sending to an output device, the circumstances in which it is viewed and factors that affect observation.

https://en.wikipedia.org/wiki/Color_model

Colour notation

Colour notation refers to the method used by colour models to identify and store colour values in a form recognisable to both computers and humans.

Colour models and notation
  • The RGB colour model uses both decimal and hexadecimal triplets for colour notation.
    • Decimal RGB colour value for orange is: R=255, G=128, B=0.
    • Hexadecimal RGB notation for orange is: #FF8000.
  • The HSB colour model uses decimal triplets for colour notation.
    • Decimal HSB colour value for orange is: H=30.12, S=100, B=100.
  • The CMYK colour model uses decimal quadruplets for colour notation.
    • The CMYK colour value for orange is: C=0, M=61.48, Y=100, K=0.
RGB colour notation

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 is made up of 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 is 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 as follows, 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.
  • The hexadecimal notation uses 16 digits from 0 to F as follows, 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 as follows 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1A, 1B, 1C, 1D, 1E and 1F.
RGB decimal notation
  • In decimal notation, an RGB triplet is used to represent the values of red, then 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 notation
  • In hexadecimal notation an RGB triplet is used to represent the value of red, then 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
References
  • https://en.wikipedia.org/wiki/Comparison_of_color_models_in_computer_graphics

Colour space

A colour space refers to a method used to organize the relationship between a range of colours in a recognisable and reproducible way.

About colour spaces
  • A colour space can be defined by assigning a set of colour swatches with names or numbers. This is the type of space used by the Pantone colour collection.
  • When an artist chooses a limited number of oil paints to add to their palette they establish a colour space within which they plan to work.
  • A digital colour space is defined mathematically or programmatically to produce a range of inter-related colours each with its own colour value.
  • Digital colour spaces are often used to define the range of colours that can be produced by a particular device (eg. printer or projector) or file type (eg. JPEG file).
About the Adobe RGB colour space
  • The Adobe RGB (1998) colour space is designed to encompass the colours that can be output by CMYK colour printers.
  • When the RGB colours model is used on a modern computer screen, the Adobe RGB (1998) colour space encompasses roughly 50% of the range of colours seen by an observer.
  • The Adobe RGB (1998) colour space improves on the gamut of the sRGB colour space, primarily in cyan-green hues.
References
  • https://en.wikipedia.org/wiki/Adobe_RGB_color_space>
  • https://en.wikipedia.org/wiki/Pantone
  • https://en.wikipedia.org/wiki/CIELAB_color_space

Colour values

Colour values are the sets of numbers and/or characters used by colour models to systematically identify and store colour information in a form of colour notation recognisable to both computers and humans. Every colour within a colour model is assigned its own unique colour value.

Colour models and notation

The RGB colour model uses both decimal and hexadecimal triplets for colour notation.

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

The HSB colour model uses decimal triplets for colour notation.

  • The decimal HSB colour value for orange is: H=30.12, S=100, B=100.

The CMYK colour model uses decimal quadruplets for colour notation.

  • The CMYK colour value for orange is: C=0, M=61.48, Y=100, K=0.
RGB colour notation

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 is made up of 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 as follows, 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.
  • The hexadecimal notation uses 16 digits from 0 to F as follows, 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 as follows 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1A, 1B, 1C, 1D, 1E and 1F.
RGB decimal notation
  • In decimal notation, an RGB triplet is used to represent the values of red, then 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 notation
  • In hexadecimal notation an RGB triplet is used to represent the value of red, then 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
References
  • https://en.wikipedia.org/wiki/Comparison_of_color_models_in_computer_graphics

Colour vision

Colour vision is the human ability to distinguish between objects based on the wavelengths of the light they emit, reflect or transmit. The human eye and brain together translate light into colour.

  • The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet. Light, however, is rarely of a single wavelength, so an observer will usually be exposed to a range of different wavelengths of light or a mixture of wavelengths from different areas of the spectrum.
  • Colours can be measured and quantified in various ways; indeed, a person’s perception of colour is a subjective process whereby the brain responds to the stimuli that are produced when incoming light reacts with several types of cone cells in the eye. In essence, different people see the same illuminated object or light source in different ways.

Colour vision

Colour vision is the human ability to distinguish between objects based on the wavelengths of the light they emit, reflect or transmit. The human eye and brain together translate light into colour.

About seeing in colour
  • 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 their eye.
About trichromatic colour vision (Trichromacy)

The trichromatic colour theory explains the system the human eye uses to see colour.

  • Trichromatic colour theory is based on the presence of three types of light-sensitive cone cells in the retina at the back of our eyes, each sensitive to a different spread of colour.
  • All the colours we observe result from the simultaneous response of all three types of cones.
  • The sensitivity of cone cells is the physiological basis for trichromatic colour vision in humans.
  • The fact that we see colour is, in the first instance, the result of interactions among the three types of cones, each of which responds with a bias towards its favoured wavelength within the visible spectrum.
  • The result is that the L, M and S cone types respond best to light with long wavelengths (biased towards 560 nm), medium wavelengths (biased towards 530 nm), and short wavelengths (biased towards 420 nm) respectively
References
  • https://en.wikipedia.org/wiki/Color_vision

Colour wheel

A colour wheel is a diagram based on a circle divided into segments. The minimum number of segments is three with a primary colour in each. Segments added between the primaries can then be used to explore the result of mixing adjacent pairs of primary colours together. Additional segments can then be added between all the existing segments to explore the result of mixing further pairs of adjacent colours.

  • 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 this small part of the electromagnetic spectrum that results in the perception of rainbow colours.
  • Colour wheels are often used in technologies which reproduce colour in ways that match the light sensitivity of the three different types of cone cells and the rod cells in the human eye.
  • Colour wheels exploring additive colour models and subtractive colour models use different sets of primary colours.
  • An RGB colour wheel, used to explore additive mixing of light, starts with red, green and blue primary colours.
  • The colours produced in between the primary colours in a colour wheel are called secondary colours.
  • The colours produced in between the secondary colours in a colour wheel are called tertiary colours.
  • A CMY colour wheel, used to explore subtractive mixing of pigments and inks (used in digital printing) starts with cyan, magenta and yellow primary colours.
  • An RYB colour wheel used to explore the subtractive mixing of art pigments and paints starts with red, yellow and blue primaries.
  • The colour wheels described above all depend on trichromatic colour vision which involves three receptor types (cone cells) processing colour stimuli.

Colour wheel

A colour wheel is a diagram based on a circle divided into segments. The minimum number of segments is three with a primary colour in each. Segments added between the primaries can then be used to explore the result of mixing adjacent pairs of primary colours together. Additional segments can then be added between all the existing segments to explore the result of mixing further pairs of adjacent colours.

  • 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 this small part of the electromagnetic spectrum that results in the perception of rainbow colours.
  • Colour wheels are often used in technologies which reproduce colour in ways that match the light sensitivity of the three different types of cone cells and the rod cells in the human eye.
  • Colour wheels exploring additive colour models and subtractive colour models use different sets of primary colours.
  • An RGB colour wheel, used to explore additive mixing of light, starts with red, green and blue primary colours.
  • The colours produced in between the primary colours in a colour wheel are called secondary colours.
  • The colours produced in between the secondary colours in a colour wheel are called tertiary colours.
  • A CMY colour wheel, used to explore subtractive mixing of pigments and inks (used in digital printing) starts with cyan, magenta and yellow primary colours.
  • An RYB colour wheel used to explore the subtractive mixing of art pigments and paints starts with red, yellow and blue primaries.
  • The colour wheels described above all depend on trichromatic colour vision which involves three receptor types (cone cells) processing colour stimuli.

https://en.wikipedia.org/wiki/Color_wheel

Complementary colours

In the context of a discussion of light, complementary colours are pairs of colours that, when mixed together produce white and when placed next to each other create the strongest contrast.

About complementary colours and colour wheels
  • Complementary colours are always opposite one another on a colour wheel.
  • The complementary colour of a primary colour is always a secondary colour on a colour wheel.
  • The pairs of primary and secondary colours that produce complementary colours depend on the colour model:
  • Whilst the secondary colours in a subtractive RYB colour wheel are green, purple and orange, mixing pigments (eg. paints or inks) is a complicated business.
  • Combinations of two complementary colours of light at full intensity produces white.
Complementary colours and the the RGB colour model
  • When using the RGB colour model, the primary/secondary pairs of complementary colours are red-cyan, green-magenta and blue-yellow.
  • Combining the wavelengths corresponding with all three RGB primary colours produces the impression of white for a human observer.
  • When working with the RGB colour model the secondary colour that pairs with any primary colour is produced by mixing the other two primaries together.

https://en.wikipedia.org/wiki/Complementary_colors

Compound

A compound is a substance made from the combination of two or more elements and held together by chemical bonds that are difficult to break. The bonds form as a result of sharing or exchanging electrons among atoms. The smallest unbreakable unit of a compound is a molecule.

  • A compound is formed when different elements react with each other, forming bonds between atoms that produce molecules.  When a compound is exposed to a new element further reactions can take place which produce new compounds.
  • A compound differs from a mixture because the atoms in a mixture are not bonded together. In this case, different elements mix together but no chemical reaction takes place, so each element remains separate and distinct.

Cone cell

Cone cells, or cones, are one of three types of photoreceptor cells (neurons) in the retina of the human eye. They are responsible for colour vision and function best in relatively bright light, as opposed to rod cells, which work better in dim light.

  • Cone cells are cone-shaped whilst rod cells are rod-shaped.
  • Cone cells are most concentrated towards the macula and densely packed in the fovea centralis, but reduce in number towards the periphery of the retina.
  • There are believed to be around six million cone cells in the human retina.