3D display systems are visual and optical systems designed to present an impression, representation or experience of three-dimensional space. They range from conventional stereoscopic screens and 3D cinema to autostereoscopic, light-field, holographic, volumetric and virtual-reality displays.
There is no single form of 3D display. Different systems reproduce different combinations of perspective and depth cues, use different viewing arrangements, and provide very different relationships between the observer, image surface and represented spatial reality.
Some 3D displays provide separate images to the two eyes. Others change the image according to viewing position, create images within an apparent volume, surround the observer with a wide field of view, or combine several of these methods. The resulting degree and type of three-dimensional appearance therefore depends upon the complete capture, representation, display and viewing system.
What Is a 3D Display System?
A 3D display system is a system for presenting visual information in a form that conveys spatial depth or three-dimensional structure.
The displayed image may remain physically located on a flat screen while producing a strong illusion of depth, or the system may employ curved, volumetric, holographic or near-eye arrangements that provide additional spatial information.
Three-dimensional appearance can be produced using monocular perspective cues, binocular cues, multiple viewing angles, movement, focus, parallax, changing viewpoint, wide field of view and other visual or optical processes.
Consequently, the term 3D display refers to a family of perspective technologies rather than to one universal display method.
3D Does Not Mean Stereoscopic Alone
A common mistake is to equate 3D exclusively with stereoscopic vision.
Stereoscopy is one important way of adding depth to a displayed image, but human beings can perceive convincing three-dimensional space from many other cues. Ordinary paintings, perspective drawings, photographs, films and television images can produce strong impressions of depth even when both eyes receive essentially the same image.
Such images employ monocular perspective information including diminution of size, foreshortening, occlusion, convergence, texture, light and shade, aerial perspective and other depth cues.
A 3D display should therefore be understood according to which depth and perspective cues it actually provides, rather than simply whether it is described as “3D”.
Principal Types of 3D Display
The Dictionary of Perspective identifies several principal forms of 3D display system, including:
- Stereoscopic 3D displays
- Light-field 3D displays
- Lenticular and autostereoscopic displays
- Holographic 3D displays
- Swept-plane and volumetric displays
- Virtual or near-eye 3D displays
These groups can overlap. A particular system may combine binocular, multi-view, virtual, optical and computational processes within the same complete perspective system.
Stereoscopic 3D Displays
Stereoscopic displays present different but corresponding perspective images to the left and right eyes.
Because the two images represent slightly different viewpoints, binocular disparity can provide the visual system with information from which stereoscopic depth or stereopsis is perceived.
This principle is used in stereoscopic photographs, 3D cinema, head-mounted displays and many virtual- and augmented-reality systems.
Stereoscopic depth is nevertheless only one component of spatial realism. The displayed scene also normally contains monocular perspective cues, and the relationship between the stereoscopic image, viewing position, scale, field of view and display geometry can substantially affect the result.
Autostereoscopic 3D Displays
Autostereoscopic displays attempt to provide separate left-eye and right-eye image information without requiring conventional stereoscopic glasses.
Lenticular screens and related directional-display methods can direct different image information towards different viewing positions, producing binocular parallax and a stereoscopic appearance.
The effective result depends strongly upon observer position. The viewing region may be divided into zones within which particular image views are delivered to the eyes.
Lenticular 3D Displays
A lenticular 3D display uses an array of small lenses to direct different parts of an underlying image towards different viewing directions.
Different images can therefore be delivered to the two eyes or to observers occupying different positions. The resulting effect can provide stereoscopic or parallax-based depth without conventional 3D glasses.
Lenticular technology demonstrates an important principle of 3D display design: the image presented to the observer can be made direction-dependent rather than remaining identical from every viewing position.
Light-Field 3D Displays
Light-field displays attempt to reproduce a more extensive set of directional light information than a conventional flat screen.
Instead of presenting only one fixed image surface, a light-field system can provide different visual information according to direction and may combine stereoscopic information with additional focusing or viewpoint-related depth cues.
The aim is to reproduce more of the structured optical information associated with viewing three-dimensional spatial reality.
Holographic 3D Displays
Holographic displays represent another important approach to 3D imaging. Holographic images can provide different image information from different viewing positions and therefore support multi-angular depth information.
A multi-angular holographic image may provide combinations of monocular perspective, stereoscopic information, binocular parallax, changing viewpoint and changing visible object form as the observer moves.
Holographic perspective is therefore fundamentally different from displaying a single fixed stereoscopic pair. The observer may obtain a succession of different perspective views rather than only two predetermined images.
However, even holographic systems do not automatically reproduce every depth cue present in direct physical vision. The realism of a holographic display depends upon factors such as viewing-angle range, resolution, focus behaviour, scale, movement and the optical characteristics of the displayed image.
Volumetric 3D Displays
Volumetric displays generate visible image information within, across or apparently occupying a three-dimensional volume rather than limiting the complete display to an ordinary flat image surface.
Some volumetric systems allow displayed content to be observed from multiple directions. The resulting image may therefore possess a different relationship with the surrounding physical space from that of an ordinary television or cinema screen.
It is important, however, to distinguish a genuinely viewpoint-dependent multi-view display from a spatially extended screen that merely presents the same fixed image to observers at different positions.
Swept-Plane 3D Displays
A swept-plane display is one form of volumetric display in which a rapidly moving or rotating display surface creates an apparent volume of light.
A succession of two-dimensional image sections is presented at changing physical positions so rapidly that the observer perceives an apparently three-dimensional illuminated form.
Such systems can permit viewing from a wide range of directions and illustrate how temporal image sequencing can be combined with physical display geometry to produce a volumetric appearance.
Virtual Reality Displays
Virtual-reality displays normally use near-eye screens or optical projection systems to provide computer-generated views directly within the observer’s field of vision.
Separate left-eye and right-eye images can provide stereoscopic depth, while head tracking allows the displayed perspective to change continuously as the user moves or turns.
This changing relationship between observer and represented space is particularly important. Rather than merely looking at one fixed image, the user can explore a computational spatial model from a potentially very large number of changing viewpoints.
Virtual reality can therefore combine stereoscopy, perspective projection, changing viewpoint, motion, wide field of view and apparent immersion within one integrated display system.
Augmented and Mixed-Reality Displays
Augmented and mixed-reality displays combine visual information from physical spatial reality with additional represented or computational image information.
The artificial image must be positioned, scaled and transformed in relation to the observer and surrounding physical environment if it is to appear spatially coherent.
These systems therefore combine several perspective processes: direct viewing of physical reality, computational generation or transformation of imagery, optical display, and final perception through the human visual system.
Near-Eye and Distant 3D Displays
3D displays can also be classified according to their distance from the observer.
- Near-eye displays place the display or optical system close to the eyes, as in virtual- and augmented-reality headsets.
- Distant displays are viewed across ordinary physical space, as with stereoscopic cinema screens, televisions, monitors and large public displays.
This distinction affects apparent field of view, image scale, optical arrangement, viewing position and the relationship between displayed image space and the observer’s physical environment.
Flat, Curved and Volumetric Displays
The physical geometry of the display surface is another important part of 3D display design.
A display may be:
- flat or planar;
- curved, cylindrical or spherical;
- volumetric; or
- based upon another real-space, projected or optical image arrangement.
The geometry of the screen and the geometry of the displayed perspective image are not the same thing. A curved screen does not automatically contain a curved or multi-view perspective image, just as a flat display can present imagery constructed using many different projection systems.
Curved Screens and Immersive Displays
Large curved, cylindrical and spherical displays can extend imagery across a much greater portion of the observer’s visual field than an ordinary flat screen.
This can produce a powerful sense of spatial enclosure and apparent immersion. Cinema systems, dome theatres, panoramic displays, LED volumes and large surrounding screen environments exploit this relationship.
However, a surrounding display is not necessarily a genuine multi-view display. If every observer sees the same fixed image regardless of position, the physical screen may be spatially extended while the image itself remains essentially uni-angular.
A genuinely multi-view system must additionally provide different viewpoint-dependent image information to different observer positions.
Uni-Angular and Multi-Angular 3D Displays
An important distinction in 3D display systems concerns the number of perspective viewing angles provided by the displayed image.
A uni-angular image represents a scene from one principal viewing position or viewing arrangement. A conventional perspective image on a monitor is a familiar example.
A multi-angular image provides different perspective information for different viewing positions. As an observer moves, previously hidden surfaces may become visible, projected shapes may change and other viewpoint-dependent perspective phenomena can occur.
This distinction is fundamental because physically walking around a fixed 2D picture does not transform it into a genuine multi-angular image.
Three Different Display Relationships
3D display systems can be understood by distinguishing three broad relationships between image and observer:
- Uni-angular viewing of a uni-angular image — an ordinary fixed perspective image is viewed from a conventional position.
- Multi-angular viewing of a uni-angular image — the observer can move around or across a physically extended display, but the displayed image itself does not change according to viewpoint.
- Multi-angular viewing of viewpoint-dependent images — different observer positions receive different image information, allowing genuine image-based angular parallax and additional perspective changes.
The third arrangement provides a fundamentally different kind of perspective experience because observer movement can alter the represented view itself.
Depth Cues in 3D Displays
The apparent realism of a 3D display depends greatly upon the depth cues it provides.
These may include:
- perspective of form;
- diminution of size;
- foreshortening;
- occlusion;
- texture gradients;
- light and shade;
- motion parallax;
- binocular disparity and stereopsis;
- binocular vergence;
- focus-related information;
- changing viewpoint;
- changing visible shape; and
- wide-field and peripheral visual information.
No single display technology necessarily reproduces all of these cues. Different 3D systems therefore create different forms and degrees of spatial realism.
Field of View and 3D Display
Field of view is especially important in immersive 3D display systems.
A small distant display occupies only a limited part of the observer’s visual field, while a large, curved, spherical or near-eye display can present imagery across a much greater angular range.
Increasing the displayed field of view can strengthen the impression that represented space surrounds the observer rather than appearing only within a framed window.
However, field of view alone does not determine whether a display is genuinely multi-view or stereoscopic. It represents one dimension of the complete perspective display system.
Display Resolution and Spatial Realism
The resolution of a 3D display affects the amount of spatial and visual detail that can be presented.
Resolution interacts with screen size, viewing distance, field of view, image scale and the resolving ability of the observer. A system with a very wide field of view may require correspondingly large amounts of image information if fine detail is to remain visible across that field.
Spatial realism therefore depends not merely upon whether a display is stereoscopic or volumetric but upon the combined performance of the complete imaging and viewing system.
3D Display, Image Space and Object Space
A 3D display establishes a relationship between represented image space and the spatial reality or model from which that image derives.
The original target may be a real physical scene, a computational three-dimensional model, an imaginary environment or a combination of real and represented spaces.
Between this target space and the observer may lie several intermediate perspective processes: camera capture, mathematical transformation, rendering, image storage, projection, display geometry and finally human visual perception.
Understanding a 3D display therefore requires examination of the complete perspective image chain, not simply the final screen.
3D Display Systems and Perspective
Every 3D display is fundamentally a perspective system because it establishes relationships between spatial information, viewpoints, images, projection or display geometry, and an observer.
The displayed content may employ linear, curvilinear, spherical, panoramic, stereoscopic, multi-view or other forms of perspective. The final appearance depends upon how these image forms interact with the physical display and the human visual system.
A display therefore cannot be evaluated solely by its physical shape. The perspective geometry of the image and the geometry of the display must be considered together.
3D Display Systems and Perspective Category Theory
Within Perspective Category Theory, a modern 3D display can involve several perspective categories operating together or in sequence.
Mathematical Perspective may calculate the spatial transformations. New Media Perspective may generate, process or link the digital views. Instrument Perspective may capture, project or display the image. Optical Perspective describes the formation and transmission of visual images, while Visual Perspective Type 2 concerns the final retinal and perceptual experience of the human observer.
Virtual, stereoscopic, holographic and mixed-reality systems are therefore often examples of complex perspective processes rather than isolated technologies belonging to only one category.
3D Displays, Illusion and Immersion
Two important functions of 3D display systems are the creation of spatial illusion and the production of apparent immersion.
A stereoscopic screen may create an illusion that objects extend in front of or behind the physical display surface. A panoramic or spherical display may expand the represented environment around the observer. A virtual-reality system may continuously reconstruct perspective views as the observer turns or moves, creating a stronger apparent relationship between the user’s position and the represented space.
These are different kinds of three-dimensional experience and should not automatically be grouped together as though they were optically or geometrically identical.
How Realistic Can a 3D Display Be?
The most complete reproduction of spatial reality would require a very large combination of the depth, optical, movement and perspective cues available during natural viewing.
Current display methods reproduce only selected parts of this information. Stereoscopic systems provide important binocular cues but not every natural visual cue. Holographic and multi-view systems can add changing-viewpoint information. Virtual reality can combine stereoscopy, movement and wide-field perspective, but still operates within technical limits of display, resolution, optics and image generation.
There is therefore no single universally “true” 3D display. Different systems reproduce different aspects of three-dimensional visual experience.
3D Display Systems — Frequently Asked Questions
What is a 3D display system?
A 3D display system is a visual, optical or computational system designed to convey spatial depth or three-dimensional structure through one or more perspective and depth cues.
What are the main types of 3D display?
Major types include stereoscopic, autostereoscopic or lenticular, light-field, holographic, volumetric or swept-plane, and virtual or near-eye 3D displays.
Are all 3D displays stereoscopic?
No. Stereoscopic displays use separate left-eye and right-eye information, but other systems may use multi-view, holographic, volumetric, motion, monocular perspective or other depth cues.
What is an autostereoscopic display?
An autostereoscopic display provides different image information to the two eyes without requiring conventional stereoscopic glasses. Lenticular and directional-display systems are examples.
What is a volumetric display?
A volumetric display presents visible image information within, across or apparently occupying a three-dimensional volume rather than restricting the complete image to one ordinary flat screen plane.
Is a curved screen a true 3D display?
A curved screen can create a wide-field or immersive appearance, but curvature alone does not make the displayed image genuinely multi-view. A true multi-view display must provide different viewpoint-dependent image information to different observer positions.
What is the difference between stereoscopic and multi-view 3D?
A conventional stereoscopic system normally presents two related views, one to each eye. A multi-view system can provide additional perspective views corresponding to different observer positions, allowing the represented scene to change as viewpoint changes.
Why is perspective important to 3D displays?
Perspective determines how spatial objects and scenes are transformed into views and images from particular viewpoints. 3D displays depend upon these relationships to generate monocular, binocular, multi-view and immersive representations of spatial reality.
The Future of 3D Display Systems
The development of 3D displays can be understood as a continuing attempt to reproduce, extend or reorganise the spatial information available in natural vision.
Conventional perspective images provide powerful monocular depth. Stereoscopy adds binocular disparity. Multi-view and holographic systems add changing perspective with viewpoint. Volumetric systems alter the physical relationship between image and display space, while virtual and mixed-reality systems dynamically connect represented space with the observer’s position and movement.
Seen in this wider context, the history and future of 3D display systems form part of the larger history of perspective: the continuing search for more powerful ways to view, represent, communicate and apparently enter three-dimensional spatial reality.