frequently appear to have little or no colour. What is it then that gives rise to the appearance of colour in these objects? The answer lies in the demonstrations of Newton that 'white' light contains all the wavelengths within the visible spectrum, and the fact that when light falls on the objects in the real world it is diminished by them.
For an observer to see an object, it is necessary for him/her to receive a complex pattern of light rays which have come from that object and contain the information required. Yet the majority of object do not in themselves emit light, as can be demonstrated easily by removing any sources of light energy. It is quite obvious, therefore, that the light necessary for colour perception generally comes from an outside source of energy and it is the way in which this is altered by the object that determines the colour that is seen.
When light waves fall on an object the following possibilities arise. They may be: transmitted, reflected, absorbed, or any combination of the three. These possibilities are illustrated in Figure 1.2. In the case of combination, a proportion of the light waves are shown to be reflected from the surface, a proportion are absorbed, and the remainder pass through the sample (transmitted) to be reflected back from the underlining surface. The combination case is typical of a transparent ink printed on paper.