1.1  Fundamentals of stereo visualization

The word “stereo” is derived from the Greek term “stereos” which can be translated by “solid” or “hard”. In the french language, this term gradually evolved to “stère de bois” which corresponds to a volumetric unit for a pile of wood. Stereo visualization thus refers to the visual perception of the solid three-dimensional (3D) properties of some objects. Developments in stereo visualization were initiated in 1838 when Sir Charles Wheatstone described the “Phenomena of Binocular Vision” [103]. Binocular vision relates to the interpretation of two slightly different views of the same object seen by both human eyes. From two different views, Wheatstone showed that the viewer can mentally reconstruct the object in three dimensions. To illustrate the concept, Wheatstone prototyped a device known as the “stereoscope”, which paints two different images of the same object directly onto the viewer retina. The initial implementation of the stereoscope, illustrated by Figure 1.1 is composed of two mirrors, A and A’, that project onto both eyes, the image of two different hand-drawn views E and E’ of a wire-frame cube. It is interesting to note that these early developments in stereoscopic visualization were made prior to the invention of photography.

Figure 1.1 The initial implementation of the stereoscope is based on two mirrors that project two views of the same object onto both human eyes. From these two views, the human visual system mentally derives a three-dimensional representation of the cube.

The presented conceptual principle that relates two 2D images to a 3D representation of an object, can be extended. More specifically, it can be intuitively deduced that a more accurate 3D description of the object can be obtained from a set a multiple views. Therefore, stereoscopic 3D properties of a scene can be derived from multiple views or multi-view images captured by a set of multiple cameras. For example, the background and foreground orientation and the relative positions of objects in the 3D scene can be extracted by analyzing the multi-view images. Starting with this elementary concept, we can now outline several applications for multi-view images.