Lighting-Viewing Methods

This chapter provides qualitative descriptions of a variety of lighting and viewing methods (LVMs). These are presented in alphabetical order, since there is no natural structure for such a list (Table 40.1 ). There are usually five elements within an image acquisition sub-system: light source, illumination optics, image-enhancement optics, main lens and sensor. The positions of these relative to each other and the object being observed must be carefully selected, to obtain a digital image that is easy to process electronically. The physical layout of the optical sub-system and the choice of appropriate components are of equal importance. Chapter 7 describes the light sources available, while optical components are discussed in Chaps.​ 5 and 6. Scanners and cameras and are described in Chaps.​ 9 and 10 respectively. Chapter 8 explains some of the concepts necessary to appreciate the methods described here. Of particular note is that of an illumination diagram. This explains, in graphical form, the shape and position and of the light source in relation to the widget and camera. Notice that the diagrams included in this chapter are not drawn to scale; they merely suggest a design for the lighting-viewing sub-system in broad conceptual terms. A multitude of combinations of the methods described below is possible.

When designing the image acquisition sub-system, a vision engineer should normally follows the following steps:

Step (1) is very simple, yet it is always in danger of being omitted. The phrase that summarises this design process is “Experiment, look and observe”. Over a period of many years, involving numerous applications, the author has found this procedure to be very effective indeed. Never attempt to design an image acquisition system without moving from the desk!.