Signal Processing for Stereoscopic and Multi-View 3D Displays - Signal Processing Systems - page 9

textures. An example of mesh representation is shown in Fig. 3 d . More details on
3D scene representation formats can be found in [ 17 , 20 ] .

2.2 3D Displays

Three-dimensional displays are ones which aim to show a visually indistinguishable
copy of a real 3D scene. The ideal 3D display would recreate all depth cues of a
scene, regardless of their importance or applicability in a particular use scenario. In
practice, due to design constraints, only a subset of the depth cues is recreated.
Most often, a display earns its “3D” label by being able to provide separate
image for each eye of the observer. In a good stereoscopic pair, objects appear on
different horizontal coordinates in each image. The horizontal offset between the
observations is known as display disparity . When a stereoscopic image is observed,
display disparity induces retinal disparity, which in turn creates the stereoscopic
illusion of depth. The illusory distance to the object created by the stereoscopic
effect is called apparent depth . Positive disparity creates apparent depth behind the
screen plane and negative disparity creates apparent depth in front of the screen.
Most contemporary 3D displays do not recreate head parallax. Some models
can present limited head parallax by casting different images towards a set of
observation angles, usually limited to a horizontal head parallax only. Note, that by
using head-tracking it is possible to present a scene from different perspectives on
a monoscopic display, thus generating head parallax without binocular depth cues
[ 24 ] . Focal depth cues are very rarely recreated by 3D displays. One exception is
the stereo display prototype with multiple focal distances described in [ 25 ] . Finally,
pictorial depth cues can be recreated by most 2D and 3D displays (volumetric LED
cube displays [ 26 ] being an exception). More information about various types of 3D
displays can be found in [ 27 - 30 ] .

2.2.1 Classification

A general taxonomy of 3D displays divides them into three basic types; holographic,
volumetric and multiple-image screens [ 27 , 28 , 31 ] . Holographic displays use
holographic methods to reconstruct the light field of a scene, volumetric displays
attempt to approximate a 3D scene by light elements (voxels) positioned in 3D
space and multiple image screens cast a number of different images, each one seen
from a different angle. There are two types of multiple-image screens. The first
type works by tracking the observer's eyes and utilizes steerable optics to beam
different images towards each eye. The second type uses fixed optics and beams a
number of different images (called “ views ”) in different directions; the directions
are selected in such way that the eyes of an observer standing in front of the screen
perceive different images. In [ 27 ] these two types are said to create eye-gaze-related
image and fixed-plane image correspondingly. The taxonomy in [ 28 ] is different;