**2. Space**

Hundreds of years of spatial representation using linear perspective led us to accept the cyclopean model in which everything is seen from a single point. The viewing hole in Filippo Brunelleschi's *tavoletta*, the single point of view used by Leon Battista Alberti (1404–1472) in his perspective method, and all the subsequent perspectivist developments are a demonstration of a dioptrical approach to the representation of three-dimensional space. Like projecting a scene through a lens, light passes through the focal point. Even in photography and its correlates, the cinematographic camera or the virtual camera in computer graphics software, the single point of view is imposed. It is an egocentric position, the center of the world. Perspective is a shackle. The holographic space breaks with this geometric convention.

In my synthetic hologram, *Tractatus Holographis* (2005), I presented a fictitious 16th century treatise on holography (Figure 1). Written in Middle French and containing animated 3D illustrations, a page turns when the viewer moves laterally. On the first and second page, the traditional perspective model is presented with its pyramidal field of view emanating from a single point. On the third page is a short explanation of the holographic setup and on the fourth page is an illustration of the holographic space as two joined truncated pyramids (for an analysis of the holographic space, see: Pepper 1989).

**Figure 1.** Tractatus Holographis, 2005. Two views of the synthetic hologram, 60 cm × 40 cm, created by author. (see: http://www.i-jacques.com/tractatusen.html).

The traditional perspective model places the viewer in the center of the world at a pivot point from which a single angle of view is projected on a plane. Instead, by reconstructing the light waves originating from a scene, holography creates a field in which the viewer can move freely and observe

the hologram content from many angles of view. The holographic *dispositif* transfers the pivot point to the hologram window and, therefore, expands the viewer's freedom of observation.

This is an important feature of the holographic *dispositif* that has significant consequences on its aesthetics and creative possibilities. The multiple perspectives of this continuous parallax optical system are what will usually define the holographic space as three-dimensional, or "3D". As an artistic representation, it means that what you see from here is different than what you see from there, that the frontal centered axis of view is only one angle among many others. Content can become variable with the viewer's movements without cinematic or mechanical animation.

In fact, this three-dimensionality affects the construction of a scene for holography in an unexpected manner. Voids occupy real optical three-dimensional spaces that determine the visibility of forms and the spatial relationship with the viewer. In the composition of a 3D holographic image, voids are not simply emptiness; they are volumes of space that are constructed by the artist to make "this" visible from "there".

Production techniques and the direction of illumination define whether the holograms are "transmission" or "reflection". Differentiating between these two types of holograms, Stephen A. Benton and V. Michael Bove, in their book *Holographic Imaging* (Benton and Bove 2008), present the analogy of holograms that are "windowlike" for transmission holograms, and "mirrorlike" for reflection holograms. Most holograms exhibited in art are "reflection holograms", which means that they are illuminated from the front. While these two categories refer to the orientation of illumination in the holographic process, this analogy can be extended to the holographic *dispositif.* Moving in front of a hologram, the viewer will see a variation of perspectives similar to the perspective variations that we see when we move in front of a mirror. Moreover, when we look at the history of the art of spatial representation, the mirror is sometimes referred to as an ideal. Alberti suggests using a mirror as a visual tool. The architect and sculptor Filarete (c.1400–c.1469), commenting on Brunelleschi's experiment on perspective, writes: "*It is certainly a subtle and beautiful thing to discover how to do it by rule from what the mirror shows you*". And for Leonardo Da Vinci (1452–1519), the mirror is "the painter's master". From a dioptric model, holography seems to reach into a catoptric model. While we can establish a comparison with images of the 2D world or sculptures of the 3D world, the holographic space is different because it is essentially an optical field in front and behind the hologram plane. When, in the 1990s, 3D computer graphics became accessible, it was often said that the artist had to think in 3D. In holography, the artist has to think spatially.
