Dictionary tag: C

To find out exactly what a colour model is then start here !!

• The primary colours in the CMY colour model are cyan, magenta and yellow.
• The CMY colour model is a subtractive colour model used with transparent or translucent inks or filters.
• The CMY colour model along with its system of notation enables an exact and reproducible approach to colour printing and other similar applications.
• The CMY colour model is deeply embedded in all contemporary digital printer technologies and underpins industrial standards for the printing industry.

Subtractive colour mixing

• The CMY colour model can be explained by imagining that an observer is presented with a well-illuminated surface such as a highly reflective sheet of white paper.
• In the diagram below a torch is used to illuminate the paper, producing a round pool of light.
• The surface appears white because it is illuminated by white light, so by light containing all the wavelengths of the visible spectrum.
• Cyan, magenta and yellow filters or inks are then placed between the light source and the paper or between the paper and the observer.
• The diagram below shows the effect of placing the filters or patches of ink onto the paper so they partially overlap.

• Where pairs of the primary coloured C, M and Y filters/inks overlap they produce secondary colours and where all three overlap, all wavelengths of light are blocked producing a dark area in the centre.
  • • A red filter will transmit red light but absorbs all other colours including green and blue.
    • A green filter will transmit green light but absorbs all other colours including blue and red.
    • A blue filter will transmit blue light but absorbs all other colours including red and green.

• Where two overlapping filters are placed between the light source and the paper or between the paper and the observer the results are as follows:
  • A red filter absorbs both green and blue and a green filter absorbs blue and red, as a result, red, green and blue are all absorbed where they overlap and that area appears black.
  • A green filter absorbs both blue and red and a green filter absorbs blue and red, as a result, red, green and blue are all absorbed where they overlap and that area appears black.
  • A blue filter absorbs both red and green and a red filter absorbs green and blue, as a result, red,  green and blue are all absorbed where they overlap and that area appears black.

• Where all three filters are placed between the light source and the paper or between the paper and the observer the result is that red, green and blue are all absorbed where they overlap and that area appears black.

• Cyan, magenta and yellow filters that correspond with the secondary colours in the RGB colour model but are the primary colours in the CMY colour model behave as follows.
  • A cyan filter absorbs red but transmits green and blue light. Green and blue together appear cyan to the human eye.
  • A magenta filter absorbs green but transmits red and blue light. Red and blue together appear magenta to the human eye.
  • A yellow filter absorbs blue but transmits red and green light. Red and green together appear yellow to the human eye.

• Lastly, where two overlapping CYK filters are placed between the light source and the paper or between the paper and the observer so that they overlap, the results are as follows:
• A cyan filter transmits green and blue light whilst a magenta filter transmits red and blue. Green and red cancel out producing blue.
• A magenta filter transmits red and blue light whilst a yellow filter transmits red and green. Blue and green cancel out producing red.
• A yellow filter transmits red and green light whilst a cyan filter transmits green and blue light.  Red and blue cancel out producing green.

CMY and the trichromatic colour model

• • • To make sense of the physiological basis of the CMY colour model we to relate it to how the trichromatic colour model explains colour vision.
    • The trichromatic colour theory established that there are three types of cone cells in the human eye that carry out the initial stage of colour processing that ultimately produces the world of colours we see around us.
      • Cone cells are daylight photoreceptors which means they are able to convert light into electrical charges through a process called photo-transduction.
      • The sensitivity of cone cells was established using spectroscopy which measures which wavelengths are absorbed and which are reflected.
      • The three types of cone cells were identified along with the range of wavelength they absorbed:
        • L = Long (500–700 nm)
        • M = Medium (440 – 670 nm)
        • S = Short (380 – 540 nm)
    • Trichomatic colour theory also established the visual effect of exposing a human observer to mixtures of light produced by three monochromatic light sources, one in the red, one in the green, and one in the blue part of the spectrum.
    • It proved that by incrementally adjusting the intensity of the light produced by each source an observer can be induced to see any colour within the visible spectrum.
    • The outcome was that a match was produced between how the L, M and S cone cells responded to light of different wavelengths and calibrated mixtures of wavelengths of light corresponding with R, G and B.
    • The fact that mixtures of red, green and blue light at different levels of intensity can be used to stimulate the L, M and S cones types to produce any human observable colour underpins almost every form of colour management in practice today.

 

In the diagram torch

 

• • • ICMY works by applying and overlaying colours that partially or entirely mask the background colour (usually white). The ink reduces the range of wavelengths of light that are reflected off the paper and so the colours seen by an observer.

CMY is called a subtractive colour model because the inks “subtract” the colors red, green and blue from white light.
White light minus red leaves cyan, white light minus green leaves magenta, and white light minus blue leaves yellow. ??

<h6 style=”font-family: ‘Montserrat’, sans-serif;”>Half-tone printing<h6>

Halftone is the reprographic technique that simulates continuous-tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient-like effect.[1] “Halftone” can also be used to refer specifically to the image that is produced by this process.[1]

Where continuous-tone imagery contains an infinite range of colors or greys, the halftone process reduces visual reproductions to an image that is printed with only one color of ink, in dots of differing size (pulse-width modulation) or spacing (frequency modulation) or both. This reproduction relies on a basic optical illusion: when the halftone dots are small, the human eye interprets the patterned areas as if they were smooth tones. At a microscopic level, developed black-and-white photographic film also consists of only two colors, and not an infinite range of continuous tones. For details, see film grain.

Just as color photography evolved with the addition of filters and film layers, color printing is made possible by repeating the halftone process for each subtractive color – most commonly using what is called the “CMYK color model”.[2] The semi-opaque property of ink allows halftone dots of different colors to create another optical effect: full-color imagery.[1]

• • • Every colour created using the CMY colour model is the result of:
      • half-toning, a process in which tiny dots of each primary colour are printed in a pattern small enough that humans see solid areas of colour. Half-toning allows for a continuous variation in the colour perceived by a viewer by adjusting the number and size of dots.
    • mixing the three primary colours in different proportions and at different levels of intensity.CMYK is based on the CMY color model and is the standard model used for colour printing.
      CMYK refers to the four ink plates used in some color printing: cyan, magenta, yellow, and ‘key’ (black).

<h6 style=”font-family: ‘Montserrat’, sans-serif;”>Half-tone printing<h6>

 

• • The CMY colour model is helpful in developing an understanding of how combinations of cyan, magenta and yellow primary colours can be used to produce a wide range (gamut) of colours when light reflected off a surface and wavelengths of light are filtered out by the inks before and reaching the eyes of an observer.
  • The CMYK colour model (sometimes called four-colour or process printing) uses the same three primary colours as CMY but uses a fourth component, black ink (K), to increase the density of darker colours and blacks.
  • CMYK printing typically relies on:
    • Using white paper with good reflective properties to produce the brightest possible highlights by reflecting the maximum amount of light back towards the observer.
    • Creating highlights by using the minimum amount of coloured ink and printing without black.
    • Producing fully-saturated mid-tones by relying on the brilliance and transparency of printing inks and dyes.
    • Adding black ink when the maximum amounts of cyan, magenta and yellow are insufficient to produce rich black tones in areas of shadow and where black text is required.

The CMY colour model is a subtractive color model.
CMYK is based on the CMY color model and is the standard model used for colour printing.
CMYK refers to the four ink plates used in some color printing: cyan, magenta, yellow, and ‘key’ (black).

The CMYK model works by applying and overlaying colours that partially or entirely mask the background colour (usually white). The ink reduces the light that would otherwise be reflected.
CMY is called a subtractive colour model because the inks “subtract” the colors red, green and blue from white light.
White light minus red leaves cyan, white light minus green leaves magenta, and white light minus blue leaves yellow. ??

Colour management for a photographic workflow

• In the case of photography, the primary goal of colour management is to control the recording of original colours and determine how particular colours or entire gamuts of colour are reproduced from start to finish of the creative process.
• When producing a photo, colour management is used to achieve a consistent output across devices such as digital cameras, scanners, monitors, TV screens, computer printers and offset printing presses.
• Colour management compensates for the fact that different technologies, devices and media have distinct capacities when reproducing gamuts and intensities of colour that can result in unintended shifts in appearance.
• At the consumer level, all operating systems include some form of colour management by default.
• Most hardware and software concerned with visual design and the reproduction of images provide colour management options, that may be set by default or require configuration according to purpose.
• A comprehensive industrial standard for cross-platform colour management is the International Colour Consortium’s (ICC) colour management system.

The principal components of a colour management system include:

• A colour theory
• A colour model
• A colour space
• Colour profile/s
• Colour notation
• Colour wheel/s, colour picker/s etc.

Colour management in practice

A typical colour management workflow starts by ensuring that colours seen through a camera viewfinder are captured and digitally recorded. Editing software such as Adobe CC allows extensive choices to be made about the appearance of images. When the workflow demands it, the calibration of monitors ensures information is accurately reproduced when viewed on screen. A successful outcome is one where all the decisions made during the editing process are accurately rendered in the resulting image.

A. Image capture   B. Image editing   C. Monitoring images   D. Image output

(Attribution: https://helpx.adobe.com/nz/photoshop-elements/using/setting-color-management.html)

A. Image capture

• Digital cameras provide settings to allow colour profiles to be selected that affect how colours are recorded, these deal with:
  • White balance
  • Photo style setting includes control over sharpness, depth of field, contrast, saturation and tone (including monochrome) etc.
• Digital file formats enable control over the quantity and types of information stored about an image:
  • Raw file formats store all the recorded information without compression.
  • JPEG, TIFF and PNG use algorithms to produce a balance between file size and image quality.

B. Image editing

• Software suites such as Adobe CC allow for almost limitless choices when editing visual material.
• Applications within Adobe CC such as Photoshop and Illustrator allow workspaces to be selected prior to editing.
• A workspace in Adobe apps is an intermediate colour model-related colour space used during the editing process.
• A global setting for the colour mode of a workspace in Illustrator can be selected in the Document colour mode dialogue box during the set-up of a new document.
• Workspaces can also be temporarily switched between CMYK, HSB, RGB, Greyscale and Websafe RGB in the Colour Settings dialogue box without affecting the Document colour mode.

C. Monitoring images

• Monitor profiles control the translation of data within image files into a monitor’s colour space.
• On-screen controls may include:
  • Contrast
  • Brightness
  • Colour levels
  • Colour temperature
  • Transparency
  • Sharpness
  • Resolution
• Monitor calibration tools ensure accurate colour across the visible spectrum and fine tonal adjustment. Professional monitor calibration packages include:
  • Datacolor SpyderX
  • Calibrite ColorChecker
  • Wacom Colour Manager
  • SpectraCal Colorimeter

D. Image output

• Colour management systems use output device profiles to prepare and translate the data in edited documents to match the capabilities of an output device and ensure the best possible match.
• To ensure consistency across applications, Adobe CC provides options to be selected in the Colour Settings dialogue box that ensures all applications are synchronized to use the same device-independent colour space.
  • RGB Colour Settings options include:
    • Adobe RGB (1998)
    • Prophoto RGB
    • sRGB
  • An extensive range of CMYK colour space options are also available.

A. Lab colour space (entire visible spectrum)   B. Documents (working space)   C. Devices 

This diagram illustrates the generic colour gamuts of different types of devices and documents.

(Attribution: https://helpx.adobe.com/nz/photoshop-elements/using/setting-color-management.html)

• In a wave diagram used to illustrate electromagnetic waves, a centreline may be used to show either:
  • The point where the electric and magnetic fields intersect and so illustrating the axis along which a wave propagates.
  • A point halfway between the crest and trough of a wave and so illustrating the axis along which a wave propagates.

• Colour is what humans see in the presence of radiated or reflected light.
• The brightness of the colour of an object or surface (its colour brightness) depends on the wavelengths and intensity of light that falls on it and the amount it reflects.
• The colour brightness of a transparent or translucent medium may depend on the wavelengths and intensity of light that falls on it and the amount it transmits or reflects.
• Colour brightness often depends on 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.
• The impression of colour brightness can be affected by hue because some hues appear brighter than others to human observers. So a fully saturated yellow may appear relatively brighter than a fully saturated red or blue.

• Optical factors affecting colour brightness include:
  • The angle at which incidence light approaches a medium, object or surface.
  • The composition of incident light in terms of wavelength, frequency and energy.
  • The polarization of incident light.

• 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:
  • Adjacent colours: The presence and illumination of adjacent colours can affect both the apparent hue and brightness of a target colour.
  • Attributes of visual perception.

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:

• Decimal notation for orange: R=255, G=128, B=0.
• Hexadecimal RGB notation for orange: #FF8000.

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:

• Decimal notation for orange: H=30.12, S=100, B=100.

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:

• Decimal notation for orange: C=0, M=61.48, Y=100, K=0.

• A colour space frames the range of colours that an artist, designer or technician has available to work with.
• A colour space may aim to restrict the number of colours or establish the widest possible gamut to work with.
• A colour space is partly predetermined by factors such as the colour theory and the colour model underpinning a workflow.
• Colour spaces are an important part of colour management and are particularly useful when working with a range of equipment across a digital environment.
• Digital colour spaces are commonly used to select and work with a range of colours that can be displayed and output to digital screens and printers in a consistent or predictable way.
• When a selected colour space is to be matched with a specific digital device such as a projector or printer, the type and model can be specified during the editing process.
• When the future handling of an image is uncertain, colour profiles dedicated to sRGB or Adobe RGB can be added to a digital file to ensure accurate colour reproduction.
• A colour profile is a program that allows a piece of equipment such as a digital printer to know how to handle and process the colour information it receives so that it produces the intended colour output.

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 are:
  • 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 are:
  • 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-recognisable 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 LMS tristimulus colour values.
  • The axes of a trichromatic CIE 1931 XYZ colour space correspond with XYZ 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 visualised 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.

• Things appear to have colour because they absorb some wavelengths of light and reflect others.
• The result of wavelengths of light within the visible spectrum entering the human eye is the experience of colour for an observer.

• The chromophore is the region of a molecule where there is an energy difference between two separate molecular orbitals.
• A  molecular orbital describes the location and wave-like behaviour of an electron as it travels around the nucleus of an atom.
• If the energy difference of a chromophore falls within the range of the visible spectrum (2 to 2.75 electron volts) then it will produce colour.
• The colour produced by a surface or object corresponds with wavelengths of light that are not absorbed during its interaction with the chromophore.

• Chromatic dispersion means dispersion according to colour.
• Chromatic dispersion is the result of the relationship between wavelength and refractive index.
• When light propagates from one medium (such as air) to another (such as water or glass) every wavelength is affected to a different degree according to the refractive index of the media concerned. There result is that each wavelength changes direction and speed. In the case of a light source producing white light, the separate wavelengths fan out with red at one extreme and violet at the other.
• A familiar example of chromatic dispersion is when white light strikes raindrops and a rainbow becomes visible to an observer.
• Remember that wavelength is a property of electromagnetic radiation, whilst colour is a feature of visual perception.

• 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 object.
• The glow of the cosmic microwave background is strongest in the microwave region of the electromagnetic spectrum.
• The CMB is a remnant of the Big Bang and so dates back to the earliest history of the Universe. The radiation that it produced has taken over 13 billion years to reach earth and so to become visible to us today.
• The CMB was initially composed of gamma wave radiation of an infinitely small wavelength, but the expansion of the Universe over time means it appears today as microwave radiation.
• The CMB is detected as an emission of uniform thermal energy, a faint glow coming from all parts of the sky.

• A colour model derived from a colour theory is the how-to part of exact and reproducible approach to:
  • The way the human eye responds to light and experiences colour.
  • Managing different types of colour such as the colours produced by lights, pigments and inks.
  • Deal with the different ways colour is handled by equipment such as camera, digital screens and printers.
• Whether or not we recognise it, whenever we are working with colour, we are adopting a colour theory, a colour model and a colour space.
• A colour theory and related colour model can be used to establish terms and definitions, rules or conventions and systems of notation for encoding colours and managing their relationship with one another.
• The most practical colour models are part of everyday life and enable accurate input and output of colour information to TVs, computers, phones and printers.
• Widely used colour models include:
  • CMY colour model
  • HSB colour model
  • RGB colour model
  • Spectral colour model
  • Trichromatic colour model

A colour model enables us to:

• Make sense of colour in relation to human vision, to the world we see around us.
• Use colours in logical, predictable and repeatable ways.
• Understand how to mix a particular colour from light or pigments, inks and dyes to produce predictable results.
• Specify colours using names, codes, notation, equations etc.
• Organise and use colour for different purposes and in different contexts, eg. on fabrics, interiors or vehicles.

• 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.

• Three key factors affect the colour of an object:
  • The light source and what happens to the light on its journey towards an object.
  • What happens when light strikes a material or medium.
  • Factors related to an observer that affect the way they perceive things.