John McDaid

Applications Technical Lead,

Sales and Technical Services.

Graphic Arts & Print Markets

KAYELL AUSTRALIA

COLOUR THEORY 101

COLOUR: A INTRODUCTION

Colour is vital in our world. Often referred to as a universal language colour can sway our thinking, invoke emotional response’s and influence our subconscious. Ten million colours, this is the estimated number of colour's human photopic vision can differentiate. (1) So with customers possessing such a high sensitivity to colour variance, it is logical brand managers, printers and designers place high importance on colour consistency and repeatability.

However, colour science is often an unknown and misunderstood premise.

When asked ‘what is colour’ people regularly answer that colour is propriety of an object; the apple is red, the tree is green the sky is blue. Although correct, it is only one part of the equation.

THE COLOUR OCCURRENCE

Colour in human photopic vision has three key ingredients required for a colour occurrence (also known as a colour event); an illuminate, the object and an observer. Interestingly these three ingredients represent in three of the hard sciences; physics, chemistry, and biology.

Without all three it can be argued that there is no colour. Similar to the age-old philosophical thought; "If a tree falls in a forest and no one is around to hear it, does it make a sound?"

THE COLOUR OCCURRENCE: THE ILLUMINANT


The first participant in the three-part colour occurrence is the Illuminate; also known as our light source. The illuminate generates the energy which eventually our vision system interprets as light.

Light is a form of electromagnetic radiation, explained in quantum mechanics as an elementary particle, the photon. Each photon is born and dies with a specific energy level. The photon’s energy level does not change the speed at which the photon travels through any given medium, the speed of light is constant for all photons, regardless of energy levels. Instead, the energy level of the photon determines how fast it pulsates. (2) This pulsation is measured in wavelengths. The higher the energy level, the shorter the wavelength.

The characteristics of the illuminate have a profound effect on our experience of colour, affecting both the second and third elements in the colour occurrence. Therefore, in colour management, it is crucial that the illuminate is clearly defined and standardized. The CIE (Commission Internationale de’l’Eclairage, or the International Commission on Illumination) defines many CIE Standard Illuminates; Illuminate A, B, C and so on which stipulate colour temperature and the corresponding spectral energy.

The illuminate is our first hard-science, physics.

THE COLOUR OCCURRENCE: THE OBJECT

The second participant is the object. Light generated from the illuminate strikes the object's surface, interacting with the atoms of the object and then re-emerge. The object absorbs part of the wavelength while others are reflected. Therefore, the reflected light isn’t the same as that incoming.

In a subtractive colour model, the unabsorbed wavelength is that which remain visible.

The changes to the wavelength of the light by the atoms and molecules of the object is why we categorise the second participant within the hard-science, chemistry.

THE COLOUR OCCURRENCE: THE OBSERVER

Third and arguably the most critical and complex participant is the observer. In the human photopic vision, this begins with the eye, continues through the optic nerve and deep into the brain. Not only influenced by our biology but also psychology, human vision can be a variable that is difficult to standardise. 

The fundamental basis for all colour reproduction is the three channel design of the human retina. Our eye has three types of colour sensors, corresponding to reds, greens, and blues allowing us to reproduce colour just using three primary pigments on paper or with three primary phosphors in a monitor. The retina is a complex layer of nerve cells lining the back of your eye. The nerve cells that respond to light are called photoreceptors and come in two types, Rods, and Cones. In each eye there are about six million cones, one hundred million rods and one million nerve fibres (3) Rods provide monochromatic vision in low-light conditions, Cones are functional in bright light conditions. Cones themselves fall into three types, each having a higher response to long, medium and short light wavelengths. (4) This response to the three wavelengths is referred to as Trichromacy.

The trichromatic structure of the human retina makes possible both the additive and subtractive primary colour models. Additive, starting from black (no wavelengths) and adding portions of the three primary colours, red, green and blue until white (all wavelengths in even proportions). Subtractive, starting from white and adding our subtractive primary, cyan, magenta and yellow which subtracts wavelengths from an otherwise white light source.

Both additive and subtractive primaries work by manipulating the wavelengths that enter our eyes and stimulate our three types of cone receptors.

THE SPECTRUM

As light is a form of electromagnetic radiation and with an understanding how the human visual system responds to such radiation it is possible to quantify, measure and plot these energy levels via their wavelength (distance between wave’s peaks) into what is known as the electromagnetic spectrum.

At one end of the spectrum with high energy, short wavelengths are gamma and x-rays, around 1-nanometer ‘nm’ (one billionth of a meter). At the opposite end with low energy, long wavelengths are radio/long range radio, measured in meters to several kilometres. Human photopic vision falls between 400nm to 700nm, known as the visible spectrum.

Did you know that white light comprises of coloured light?

Pink Floyds famed 1973 cover artwork for their album ‘Dark Side of the Moon’ is a modern homage to the experiments conducted by Sir Isaac Newton in 1666. These experiments are the foundations of today’s understanding of colour. Using a prism of glass and directing daylight through at a particular angle he was able to separate the light beam into visually distinct colours. Violet, Blue, Green, Yellow, Orange, and Red.

With further experimentation, Newton drew that white light was not merely a homogeneous entity but in-fact composed of a mixture of all those colour in the spectrum. (5)

COLOUR: A SCIENCE

The topics covered above is just a drop into the ocean of colour science. Scientist today are still making discovers into the physics, chemistry, and biology of colour and the human visual system. Moreover, while modern, sophisticated colour management systems are making repeatable colour more certain variables in the process can prove challenging.     

REFERENCES

1.     Judd; Wyszecki: (1975) Colour in Business

2.     Fraser; Murphy; Bunting: (2005) Real Word Colour Management

3.     Fraser; Murphy; Bunting: (2005) Real Word Colour Management

4.     Hunt; Pointer: (2011) Measuring Colour, Forth Edition

5.     Hunt; Pointer: (2011) Measuring Colour, Forth Edition