Chemical bond

A 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

Colour

Things appear coloured 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.

The colour an observer sees depends on:

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 amplitude 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 can try and share our experiences of colour using language but colour cannot be defined without examples.

The name given to light that contains all wavelength of the visible spectrum is white light.

When white light strikes a neutral coloured object, and all wavelengths are reflected, then it appears white to an observer.

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.

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 and on which of those wavelengths are 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.

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

Colour

Things appear coloured 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.

  • 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 amplitude of visible light that strikes the retina at the back of each eye.
  • 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 and on which of those wavelengths are 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.

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 notation

The most common forms of colour notation used with computer software and by digital equipment are the triplets of the  RGB and HSB colour models and the quadruplets used by CMYK model.

  • RGB notation can be represented in decimal or hexadecimal formats.
    • Decimal RGB notation for orange is: R=255, G=128, B=0.
    • Hexadecimal RGB notation  for orange is: #FF8000.
  • HSB notation is represented in a decimal format.
    • The HSB notation for orange is: H=30.12, S=100, B=100.
  • CMYK notation is represented in a decimal format.
    • The CMYK notation for orange is: C=0, M=61.48, Y=100, K=0.

Colour vision

Colour vision is the ability of an organism or machine to distinguish objects based on the wavelengths (or frequencies) 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. But an observer’s perception of colour is a subjective process whereby their brain responds to stimuli that are produced when incoming light reacts with light-sensitive cells at the back of their eye. As a result, different people may see the same illuminated object or light source in different ways.

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

Colour vision

Colour vision is the ability of an organism or machine to distinguish objects based on the wavelengths (or frequencies) 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 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

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.

Complementary

In the context of a discussion of light (as opposed to pigments) complementary colours are two colours that, when mixed together, produce white light.

  • When working with the RGB colour model, combining the wavelengths corresponding with red, green and blue primary colours produces white for a human observer.
  • The complementary colour of each primary colour when working with the RGB colour model is the secondary colour produced by combining the other two primaries.
  • The complementary primary–secondary combinations of light are red–cyan, green–magenta, and blue–yellow.
  • Combinations of complementary primary–secondary colours at full intensity make white light because together they contain wavelengths corresponding with all three primaries.
  • A complementary colour plus a primary colour combine to produce white because each complementary colour is the product of combing two primaries.
  • So a complementary colour produced by combining green and blue primaries makes white when combined with red.

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.

  • The three types of photoreceptor cells (neurons) in the retina of the human eye are cone, rod and ganglion cells.
  • 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 and 90 million rod cells in the human retina.

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

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.

Crest

The crest is the point on a wave with the maximum value of upward displacement within a wave-cycle. A trough is the opposite of a crest, so the minimum or lowest point in a wave-cycle.

  • On a wave at sea, the crest is a point where the displacement of water is at a maximum. A trough is the opposite of a crest, so a trough is a point where the displacement of the medium is at a minimum.
  • In the case of an electromagnetic wave which has an electric and a magnetic axis then a crest on either axis refers to maximum displacement in the positive direction whilst a trough refers to minimum displacement.

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

Crest and trough

The crest is the point on a wave with the maximum value of upward displacement within a wave-cycle. A trough is the opposite of a crest, so the minimum or lowest point in a wave-cycle.

  • On a surface wave, the crest is a point where the displacement of the medium (water for example) is at a maximum. A trough is the opposite of a crest, so a trough is a point where the displacement of the medium is at a minimum.
  • In the case of an electromagnetic wave which has an electric and a magnetic axis then a crest on either axis refers to maximum displacement in the positive direction whilst a trough refers to minimum displacement.

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

Critical angle

The critical angle for light approaching the boundary between two different media is the angle of incidence above which it undergoes total internal reflection. The critical angle is measured with respect to the normal at the boundary between two media.

  • Internal reflection is a common phenomenon so far as visible light is concerned but occurs with all types of electromagnetic radiation.
  • Internal reflection takes place when light travelling through a medium strikes the boundary of another medium with a lower refractive index at an angle greater than the critical angle.
  • For example, internal reflection takes place when light reaches air from glass at an angle greater than the critical angle, but not when light reaches glass from air.
  • In general, light will be partially refracted and partially reflected because of irregularities in the surface at the boundary.
  • However, if the angle of incidence is greater than the critical angle for all points at which light strikes the boundary then no light will cross the boundary, but will instead undergo total internal reflection.

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

Critical angle

The critical angle for light approaching the boundary between two different media is the angle of incidence above which it undergoes total internal reflection. The critical angle is measured with respect to the normal at the boundary between two media.

  • Internal reflection is a common phenomenon so far as visible light is concerned but occurs with all types of electromagnetic radiation.
  • Internal reflection takes place when light travelling through a medium strikes the boundary of another medium with a lower refractive index at an angle greater than the critical angle.
  • For example, internal reflection takes place when light reaches air from glass at an angle greater than the critical angle, but not when light reaches glass from air.
  • In general, light will be partially refracted and partially reflected because of irregularities in the surface at the boundary.
  • However, if the angle of incidence is greater than the critical angle for all points at which light strikes the boundary then no light will cross the boundary, but will instead undergo total internal reflection.

Crown glass

Crown glass is a type of optical glass. It is made without lead or iron and is used in the manufacture of lenses and other tools and equipment concerned with the visible part of the electromagnetic spectrum.

  • Crown glass is produced from alkali-lime silicates containing approximately 10% potassium oxide and is one of the earliest low dispersion glasses.
  • As well as the specific material called crown glass, there are other optical glasses with similar properties that are also called crown glasses.

https://en.wikipedia.org/wiki/Crown_glass_(optics)

Cosmic Microwave Background

The Cosmic Microwave Background (CMB) is a form of electromagnetic radiation dating from an early stage of the Universe. It is the oldest known form of electromagnetic radiation. With a traditional optical telescope, the space between stars and galaxies is completely dark but a sufficiently sensitive radio telescope reveals the CMB as a faint glow not associated with any star, galaxy, or other objects.

  • The glow of the cosmic microwave background is strongest in the microwave region of the electromagnetic spectrum.
  • The CMB is an emission of uniform thermal energy coming from all parts of the sky. As a result, it is often described as being homogeneous and isotropic.
  • The CMB is considered to provide demonstrable evidence for the Big Bang theory.
  • The CMB appears in the microwave region of the spectrum today because the gamma waves emitted at the start have been stretched by the continuing expansion of the universe over time.

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

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.

Why use colour models?

  • Colour models help to relate colours to:
    • One another
    • Light sources, objects and materials
    • Experience and perception.
  • 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 model, 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. The most common colour models used by graphic designers on a day to day basis are the RGB model on their computer displays and the CMYK model for digital printing.

Remember that:

  • Seeing colour results from how our eyes process light waves.
  • In the real world, colours are changing all the time, appear differently in different situations and are infinitely variable.
  • So colour models help to make sense of a chaotic world.

What colour models do?

A colour model helps to do any of the following:

  • Decide what colours to mix to get the colour you want.
  • Know what happens when you mix two or more colours together.
  • Provide a name or code for a colour or a series of colours you want to use again.
  • Give you a list of colours produced by a rainbow or by a digital display.
  • Provide a system to mix a palette of colours from red, green and blue (RGB) or from cyan, magenta and yellow (CMY).

Spectral colour model

The spectral colour model (red, orange, yellow, green, blue, violet)  is 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 often 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 opaque pigments.

HSB colour model

HSB (hue, saturation, brightness) is a popular colour model because it is more intuitive and so easier to use when adjusting colour with digital software 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

  • Colour models are 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 printers, large when the same image is viewed on a high definition digital displays, or huge when the original scene is viewed in bright sunlight on a summer day.
  • A colour system considers all the factors that affect the observer, the colour model, how information is encoded before sending to the output device and the circumstances in which it is expected to be viewed.

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