1
Fundamentals of colour and colour vision
This chapter deals with some of the fundamental principles related to the nature of colour and how we see colour. An understanding of these principles is desirable in order to appreciate information in other chapters of the book and to recognize some of the problems associated with colour reproduction and its control.
COLOUR AND LIGHT
Colour is an experience enjoyed by almost all the human race from a very early age. As we grow we learn to recognize, and often name, specific colours such as 'sky blue' and 'postbox red' yes we can never be sure that everyone derives precisely the same sensation from a given stimulus. There are an important minority of people, especially male, with defective colour vision (said to be 'colour blind') who do not, but we generally expect that the remainder do. All we can really assume is that the sensation received is similar.
Our perception of colour is quite a colour is quite a complicated process as it results from interactions of a physical, physiological and psychological nature. When we consider the physical causes of colour it is apparent that these may be defined easily, therefore personal differences of perception are very much concerned with the physiological and psychological processes. In order to gain a full appreciation of colour theory, nd the problems of colour matching and reproduction, it is essential to consider these processes in some detail. However, before moving to this some background knowledge is required.
The physical nature of light and colour
The sensation of colour is achieved when electromagnetic waves between the limits of approximately 380 and 780 nanometres (nano = 10-9) are incident upon the eye. These particular electromagnetic waves are commonly referred to as light waves and they form the visible spectrum. Light waves are only a small part of the range of electromagnetic radiation that extends from short gamma waves at one end of the scale to broadcasting waves at the other. Figure 1.1 shows that shorter visible wavelengths produce the sensation of violet and as the wavelength increases the sensation changes to blue, green, yellow, orange and red, progressively. Thus, whenever a visual sensation is received which is red, for example, it means that the light falling on the eye has a predominance of long waves.
Having said that light which appears red contains a predominance of long waves to some extent begs a question. In the real world, the objects around us appear to have a variety of colours and yet the sources of light energy, such as daylight,