17.4 3D imaging and holographic displays

3D imaging and holographic displays are revolutionizing how we see and interact with visual information. These technologies create immersive experiences by tricking our eyes into perceiving depth and dimensionality in flat images.

From stereoscopic glasses to autostereoscopic screens and true holography, 3D displays are evolving rapidly. They're changing everything from entertainment and gaming to medical imaging and scientific visualization, pushing the boundaries of visual technology.

3D Display Technologies

Stereoscopic and Autostereoscopic Displays

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• Stereoscopy creates an illusion of depth by presenting slightly different images to each eye
  • Requires special glasses (anaglyph, polarized, or active shutter) to separate the images for each eye
  • Used in 3D movies, virtual reality headsets, and some video games (Nintendo 3DS)
• Autostereoscopic displays provide a 3D effect without the need for special glasses
  • Use parallax barriers or lenticular lenses to direct different images to each eye
  • Limited viewing angles and sweet spots where the 3D effect is optimal
  • Examples include some smartphones (LG Optimus 3D) and portable game consoles (Nintendo 3DS)

Volumetric and Light Field Displays

• Volumetric displays create 3D images in a physical space by illuminating points in a volume
  • Use rapidly moving screens, laser beams, or stacked transparent displays to create the illusion of a solid object
  • Allows viewing from multiple angles without special glasses
  • Examples include the Voxon VX1 and the Ostendo Quantum Photonic Imager
• Light field displays recreate the light rays emanating from a scene, providing depth and parallax
  • Capture and display the direction and intensity of light rays, allowing for realistic 3D representation
  • Requires a high-resolution display and significant computational power
  • Examples include the Lytro Immerge and the Avegant Light Field Display

Holography

• Holography is a technique that records and reconstructs wavefronts of light to create 3D images
  • Holograms are created by interfering a reference beam with light scattered from an object
  • The interference pattern is recorded on a photosensitive material (holographic film or plate)
  • Illuminating the hologram with the reference beam reconstructs the original wavefront, creating a 3D image
  • Examples include security holograms on credit cards and holographic art displays

Holographic Display Components

Spatial Light Modulators and Parallax Barriers

• Spatial light modulators (SLMs) are devices that can modulate the amplitude, phase, or polarization of light
  • Used in holographic displays to control the wavefront of the reconstructed light
  • Examples include liquid crystal on silicon (LCoS) and digital micromirror devices (DMDs)
• Parallax barriers are vertical slits placed in front of a display to direct different images to each eye
  • Each eye sees a different set of pixels, creating a stereoscopic effect
  • The barrier blocks some of the light, reducing the overall brightness of the display
  • Used in some autostereoscopic displays (Nintendo 3DS)

Lenticular Lenses

• Lenticular lenses are arrays of cylindrical lenses placed over a display to direct different images to each eye
  • Each lens focuses on a specific set of pixels, creating a stereoscopic effect
  • Allows for multiple viewing zones, increasing the range of viewing angles compared to parallax barriers
  • Used in some autostereoscopic displays, such as digital signage and 3D postcards

Visual Perception in 3D Displays

Depth Perception and Binocular Disparity

• Depth perception is the ability to perceive the world in three dimensions and estimate the distance of objects
  • Relies on various cues, including binocular disparity, motion parallax, and occlusion
  • Binocular disparity is the difference in the images seen by the left and right eyes due to their separation
  • The brain processes these slightly different images to create a sense of depth (stereopsis)
  • 3D displays exploit binocular disparity to create the illusion of depth

Vergence-Accommodation Conflict and Motion Parallax

• Vergence-accommodation conflict occurs when the eyes converge on a different plane than the focal plane
  • In natural vision, vergence (eye rotation) and accommodation (lens focusing) are linked
  • Most 3D displays present images on a single plane, causing a mismatch between vergence and accommodation
  • This conflict can lead to visual discomfort, eye strain, and headaches
• Motion parallax is the apparent change in the position of objects relative to each other when viewed from different angles
  • Provides depth cues based on the relative motion of objects as the viewer moves
  • Some 3D displays, such as volumetric and light field displays, can reproduce motion parallax
  • Enhances the realism and immersion of the 3D experience