# Application of Three-Dimensional Vision Technology in Dance
## 2 Three-Dimensional Vision Technology
### Three-Dimensional Vision Technology Types
#### 2.2.3 Real Three-Dimensional Vision Technology  
Real 3D vision technology can provide nearly real 3D image information and physical depth of field, which has essential research value in many fields. Currently, holographic and volumetric 3D vision technologies are the most widely researched.  
Holographic 3D vision technology records and reproduces an object's complete light field information by recording and reproducing it, thus enabling viewers to see an image with a real stereoscopic sense under specific conditions [30; 31; 32]. As shown in Figure 7, the production of holographic images requires two light beams: one is the reference light, and the other is the object light [31]. They are superimposed on the object, and interference occurs; the phase and amplitude of each point on the object are converted into varying-intensity information and recorded, forming a holographic image. When the holographic image is illuminated with appropriate light, the eyes can observe the real 3D image again. Holographic 3D vision technology can have a realistic 3D effect and a broader viewing angle range. Still, the recording and display equipment is more costly and more disturbed by ambient light.  
Volumetric 3D vision technology utilizes luminous body prime points to present the object stereoscopic sense, which is currently mainly divided into scanning 3D vision technology and solid-state 3D vision technology. In scanning 3D vision technology, a sequence of 2D images is projected onto a rotating or moving screen. At the same time, the screen moves at a speed that is imperceptible to the observer because of the human  
Figure 6: (**a**) Multi-angle parallax barrier technology (Reprinted from Ref. [15]); (**b**) column lens array technology (Reprinted from Ref. [18]); (**c**) direction backlight technology (Reprinted from Ref. [21]).  
visual holdover, which creates 3D vision [33]. Therefore, it can realize a true 3D vision in 360\({}^{\circ}\). In the system, light beams of different colors are projected onto the display medium by a light deflector, which allows for the medium to reflect a wide range of colors. At the same time, the medium allows for the light beams to produce discrete visible points, which are voxels, corresponding to any point in the 3D image. As for solid-state 3D vision technology, an excitation source shines two laser beams onto the imaging space in a transparent stereoscopic space made of a special material [34]. After refraction, the two beams of light intersect at a point, forming the smallest unit of the stereoscopic image with its physical depth of field--a voxel. Each voxel point corresponds to an actual point that constitutes a real object. When the two laser beams move rapidly, countless intersections are formed in the imaging space. In this way, the numerous voxel points constitute a true 3D vision with a real physical depth of field.  
Volumetric 3D vision technology is mainly realized by projection, interference, or imaging methods. A projection display utilizes a high-speed laser beam to project an image into space, forming a stereoscopic display [35]. Interference display produces interference patterns by overlapping two laser beams, creating a stereoscopic projection. Imaging display utilizes transparent layers and lenses to split the image into multiple layers so that images with different depths can be presented, forming a stereoscopic effect. Volumetric 3D vision can provide a 3D vision effect in the whole observation space, but the complexity and cost of this technology are high [36].