Colour Design

Theories and Applications

Janet Best, Janet Best

• Publisher: Woodhead Publishing
• Year: 2012
• ISBN:
  9780857095534
• Topic: Psychology
• Subtopic: Cognitive Psychology & Cognition
• Index: Psychology

Given its importance in analysing and influencing the world around us, an understanding of colour is a vital tool in any design process. Colour design provides a comprehensive review of the issues surrounding the use of colour, from the fundamental principles of what colour is to its important applications across a vast range of industries.Part one covers the main principles and theories of colour, focusing on the human visual system and the psychology of colour perception. Part two goes on to review colour measurement and description, including consideration of international standards, approval methods for textiles and lithographic printing, and colour communication issues. Forecasting colour trends and methods for design enhancement are then discussed in part three along with the history of colour theory, dyes and pigments, and an overview of dye and print techniques. Finally, part four considers the use of colour across a range of specific applications, from fashion, art and interiors, to food and website design.With its distinguished editor and international team of contributors, Colour design is an invaluable reference tool for all those researching or working with colour and design in any capacity.

• Provides a comprehensive review of the issues surrounding the use of colour in textiles
• Discusses the application of colour across a vast range of industries
• Chapters cover the theories, measurement and description of colour, forecasting colour trends and methods for design enhancement

Part I

Colour and colour perception

1

What is colour?

A.R. Hanson, National Physical Laboratory, UK

Abstract:

Colour is incredible! It is an important sense providing us with essential information about our world, but it is not simple. This chapter describes how we resolve light the way we do, through an attempt to create a space to contain all the colours that exist. Human colour vision is a sensation of three dimensions so the space will necessarily comprise three dimensions; however, as there are many uses of colour, several such spaces have been developed.

Key words

spectrum

hue

colour spaces

subtractive colour mixing

additive colour mixing

1.1 Introduction

Turning to dictionaries to answer the question ‘What is colour?’, the reader finds that in general it is defined by negatives: ‘the visual property of light which is not related to lightness, saturation, texture, glossiness or translucency.’ Such technical definitions underplay the enormously positive value colour brings our species and the impact it has upon us. From a survival point of view, it is the primary sense in distinguishing ripe from unripe fruit and safe from unsafe meat; it informs us of the quality of beer or honey and tells us how strong a cup of coffee is or the quality of tomato puree. It adds richness and immediacy to complex visual information, for example in maps and warning signals. It identifies football teams, snooker balls and political parties. It affects mood and performance, dominates fashion aesthetics, while its symbolism permeates fine art, national flags and corporate branding. For human beings as sensory, intellectual animals with a high proportion of information about the world surrounding us channelled through vision, colour is a highly significant component of our everyday life.

One of the most curious things about colour is its intangible nature. It is a human sense that is very hard to replicate in mathematical software or robotic hardware, and research into its complicated functionality is as active today as it has ever been. The colour we see is to some extent time-averaged: the different persistences of various phosphors in fluorescent lighting means that the colour of their illumination changes imperceptibly cyclically 100 times a second. If we stare at a static scene for about 20 seconds we see after-images. As we age, the lens in our eye, our window upon the world, yellows and (although we tend not to notice this) blues dull. Spatially, colours influence each other through the process called simultaneous contrast (Chevreul and Birren 1981). The impressionist artist Van Gogh appreciated this in his vibrant paintings, often juxtaposing complementary colours (such as blue against yellow and green against red) for enhanced effect. For various reasons, even simple colour tests will generate wide ranges of responses from the same observer at different times, and between different observers. We see colour differently according to illumination type and level. It is not unusual for a person’s left and right eye to see colour slightly differently. Taking these factors into account, one starts to realise that any model of human colour vision is going to be very complicated. At best we can create one which will work under a very limited set of conditions. Designing a machine to predict when a printed photograph matches the original scene is a very tall order. In fact, photographic film manufacturers have long known that beyond colour fidelity, their customers have a more sales-worthy colour preference. For example, there are distinct ways in which Japanese and European photographic film stock represent the colour of grass. Such is the complexity and influence of colour that some designers shy from its use (Batchelor, 2000).

To see colour involves several components – a source, a detector and usually a medium. The light source may be coloured, the eye provides discriminatory resolution over the range of visible light and the medium alters the light source colour through its optical properties (reflection, refraction, scattering, absorption, fluorescence and so on). Altering any of these components, and indeed the viewing conditions, can lead to a change in the relative and absolute colours in a scene. When a light source illuminating a scene is changed, the human visual system largely adapts, seemingly referencing colours to the whitest visible entity in the scene, in the same way that the white point may be adjusted for a digital camera or image. The human visual system performs many intriguing operations, several of which lead to odd visual effects such as simultaneous contrast mentioned previously. These are the basis of several fascinating optical illusions such as that shown in Fig. 1.1, but present considerable challenges to someone wishing to organise colour, build a machine to measure it or construct a numerical model comprehensively describing its perception.

1.1 Optical illusion demonstrating simultaneous contrast. There are only three colours in this image: black, yellow and one green.

Nassau (2001) comprehensively collates the various causes of colour in media, ranging from the chemical properties of atoms and molecules to physical optics. For example, he explains that the sky is blue (and the setting sun red) because atmospheric molecules scatter light of different wavelengths by enormously different amounts – violet light is scattered about 16 times more than red light. A scientific definition of colour is that it is a variation in the spectral power distribution of light as discriminated by the human visual system. It is qualitative perception of light.

In the rest of this chapter, we shall begin with a description of light, and how the eye has a limited range of its detection. We shall see how three sensor species within human eyes resolve the visible spectrum into three dimensions of colour, and how the nature of these three dimensions changes as neural signals move from retina to brain. Many systems are used to specify colour, each with a rationale based on the understanding of colour at the time of derivation or a particular set of observations or practicalities such as the implementation of colour mixing systems.

1.2 Visible light

Natural light illuminating human activity on earth has a range limited by the light source, and by our eyes. Light is the carriage of energy by distortions of an electromagnetic field. The field does not require a physical medium to support it – light can travel through a vacuum, as it does when moving from the sun to the earth. Light has electrical and magnetic properties, refracting and diffracting like a wave, so is called an electromagnetic wave.

It is useful to understand a little of the wave properties of light. Light can be described as having a wavelength, a frequency and a speed. Ocean waves might typically hit a beach with a frequency of 10 every minute, have a wavelength (distance between waves) of about 25 m, and travel at roughly 4 m/s (about 9 mph). In a vacuum, light of all wavelengths (or frequencies) travel at the same speed (about three thousand million metres per second or 186 thousand miles per hour) and a typical (actually bluish-green) visible wavelength of light would be about 530 millionths of a millimetre, normally described as 530 nanometres, written as 530 nm. This same blue–green light has a frequency of about 566 million million oscillations per second. From now on, this chapter will describe light in terms of wavelength (expressed in nm) only. White light is a mixture of different wavelengths. In normal dispersive materials, such as a glass and water, different wavelengths of light travel at slightly different speeds (blue light travels slower than red light) causing the splitting of spectra by prisms and rain through the process of refraction. The resulting continuum of wavelengths of visible light appears to us as different spectral colours as exhibited in a rainbow.

Three properties constrain the range of solar light illuminating us. The first is the relative spectral power distribution of the sun, which depends on its temperature. Planck’s Law can be applied to calculate – to a good approximation – the amount of light present at each wavelength, giving appreciable fluxes from the ultraviolet (UV) to the mid-infrared. Wien’s Law may be used to find the peak wavelength as a function of the surface temperature of the sun which, depending on the assumption of temperature, ranges from 480 to 520 nm. Second, fine gaps in the solar spectrum called the Fraunhofer lines are caused by gases within the sun absorbing very narrow ranges of optical wavelengths. Finally, the nature of the earth’s atmosphere and other surfaces (clouds, oceans, grasslands, etc.) reflect and absorb light by varying amounts over the spectrum. Atmospheric ozone absorbs a proportion of UV radiation while the so-called ‘greenhouse gases’ (principally water and carbon dioxide) absorb some visible and infrared wavelengths. As a result of these various factors, the final spectrum of daylight reaching us at sea level has a somewhat complicated spectral distribution.

Eye physiolo...