Image Formation

Abstract

In this chapter we discuss how images are formed and captured, the first step in robot and human perception of the world. From images we can deduce the size, shape and position of objects in the world as well as other characteristics such as color and texture.

It has long been known that a simple pin-hole is able to create a perfect inverted image on the wall of a darkened room. Some marine molluscs, for example the Nautilus, have pin-hole camera eyes. All vertebrates have a lens that forms an inverted image on the retina where the light-sensitive cells rod and cone cells, shown previously in Fig. 10.6, are arranged. A digital camera is similar in principle - a glass or plastic lens forms an image on the surface of a semiconductor chip with an array of light sensitive devices to convert light to a digital image.

The process of image formation, in an eye or in a camera, involves a projection of the 3-dimensional world onto a 2-dimensional surface. The depth information is lost and we can no longer tell from the image whether it is of a large object in the distance or a smaller closer object. This transformation from 3 to 2 dimensions is known as perspective projection and is discussed in Sect. 11.1. Section 11.2 introduces the topic of camera calibration, the estimation of the parameters of the perspective transformation. In Sect. 11.2.3 we discuss the inverse problem, how to reconstruct 3-dimensional world points given a 2-dimensional image. Section 11.3 introduces alternative types of cameras capable of wide-angle or panoramic imaging.