CMY colour model

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.