A volumetric display device is a display device that forms a visual representation of an object in three physical dimensions, as opposed to the planar image of traditional screens that simulate depth through a number of different visual effects. One definition offered by pioneers in the field, Barry Blundell and Adam Schwarz, is that volumetric displays create 3D imagery via the emission, scattering, or relaying of illumination from well-defined regions in (x,y,z) space. A true volumetric display produces in the observer a visual experience of a material object in three-dimensional space, even though no such object is present. The perceived object displays characteristics similar to an actual material object by allowing the observer to view it from any direction, to focus a camera on a specific detail, and to see perspective – meaning that the parts of the image closer to the viewer appear larger than those further away. Volumetric 3D displays are a type of autostereoscopic display, in that they provide a different view to each eye, thus creating three-dimensional imagery that can be viewed by unaided eyes. However, they have the advantage over most flat-screen autostereoscopic displays, that they are able to provide realistic focal depth in addition to providing motion parallax and vergence, thus avoiding vergence-accommodation conflict. Volumetric displays are one of several kinds of 3D displays. Other types are stereoscopes, view-sequential displays, electro-holographic displays, "two view" displays, and panoramagrams. Although first postulated in 1912, and a staple of science fiction, volumetric displays are not widely used in everyday life. There are numerous potential markets for volumetric displays with use cases including medical imaging, mining, education, advertising, simulation, video games, communication and geophysical visualisation. When compared to other 3D visualisation tools such as virtual reality, volumetric displays offer an inherently different mode of interaction, providing the opportunity for a group of people to gather around the display and interact in a natural manner without having to don 3D glasses or other head gear.
Types Many different attempts have been made to produce volumetric imaging devices. There is no officially accepted "taxonomy" of the variety of volumetric displays, an issue which is complicated by the many permutations of their characteristics. For example, illumination within a volumetric display can either reach the eye directly from the source or via an intermediate surface such as a mirror or glass; likewise, this surface, which need not be tangible, can undergo motion such as oscillation or rotation. One categorization is as follows:
Swept-volume display Swept-surface (or "swept-volume") volumetric 3D displays rely on the human persistence of vision to fuse a series of slices of the 3D object into a single 3D image. A variety of swept-volume displays have been created. For example, the 3D scene is computationally decomposed into a series of "slices", which can be rectangular, disc-shaped, or helically cross-sectioned, whereupon they are projected onto or from a display surface undergoing motion. The image on the 2D surface (created by projection onto the surface, LEDs embedded in the surface, or other techniques) changes as the surface moves or rotates. Due to the persistence of vision, humans perceive a continuous volume of light. The display surface can be reflective, transmissive, or a combination of both. Another type of 3D display that is a candidate member of the class of swept-volume 3D displays is the varifocal mirror architecture. One of the first references to this type of system is from 1966, in which a vibrating mirrored drumhead reflects a series of patterns from a high-frame-rate 2D image source, such as a vector display, to a corresponding set of depth surfaces. An example of a commercially available Swept-volume display is the Voxon VX1 from Voxon Photonics. This display has a volume area that is 18 cm × 18 cm × 8 cm (7.1 in × 7.1 in × 3.1 in) deep and can render up to 500 million voxels per second. Content for the VX1 can be created using Unity or using standard 3D file types such as OBJ, STL and DICOM for medical imaging.
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