Signal Processing - September 2016 - 123

When presenting legacy sRGB content,
the device is operated in a conventional
three primary mode without any adjustments. Therefore, the display hardware
is flexible enough to support existing
content without any tradeoffs while also
supporting emerging color spaces.
Trends in the display industry are
clear: higher resolutions and wider color
gamuts will become commonplace in
the near future. Increasing resolution
will be provided by advanced nanofabrication technology and potentially
driven by factored image generation
algorithms. Factored spectral displays,
on the other hand, provide a viable
solution for adaptive, wide color gamut
display that could be seamlessly integrated into cinematic projection systems,
home theaters, and office projectors.

DMD Projector

External, Fiber-Coupled
Light Engine

(a)
Optimized 3-D Gamut

Light field displays
Here we discuss emerging light field
Y
display technology and a number of
unconventional applications. The physical world contains light rays of diverse
intensities and colors running in various
directions. The light field is a function
that describes the amount and color of
y
x
light flowing in every direction through
every point in space. A binocular viewer moving through the light field per(b)
ceives various depth cues. Binocular
cues are created because the two eyes Figure 3. Adaptive color display with factored spectral projector. The device uses a custom light engine with
receive different light rays. Motion par- (a) six LEDs. The total addressable gamut of the display spans most of the CIE xy space, but the refresh rate
allax cues are created because the eyes of the digital micromirror device (DMD) only allows for up to four primaries to be used for any projected imreceive different rays as the viewer's age. Factored image synthesis allows for the content-specific optimal color gamut spanned by four primaries
to be computed while simultaneously solving (b) the gamut mapping problem.
head moves. Accommodation (focus)
cues are created because different parts
but different tradeoffs can be made to create reasonable approxiof the viewer's pupil receive different light rays. Light field dismations of natural light fields.
plays are intended to recreate those cues with sufficient accuraOver a century ago, Frederic Ives conceived of parallax barcy to enable a high-fidelity 3-D viewing experience.
riers [1]. A barrier mask consisting of an array of pinholes or
A light field display emits a 4-D distribution of light rays,
slits would be mounted at a slight offset in front of a display
which varies over the two spatial dimensions of a display sursuch that a viewer would perceive only a subset of the display
face but also over the horizontal and vertical viewing angle of
pixels from any given perspective. The display would render
each pixel. The display primitives of conventional displays are
an image that contains the corresponding, interlaced perspec2-D pixels (picture elements), those of volumetric or multiplane
tives of the light field. Soon after, Gabriel Lippmann built the
displays are 3-D voxels (volume elements), and those of 4-D
first light field camera and display using integral imaging [2].
light field displays are light rays, each carrying radiance at some
Instead of pinhole arrays, he mounted microlens arrays on
location into a specific direction. Figure 4 illustrates the common
photographic plates, exposed and developed these plates with
two-plane parameterization of a light field: a plane x is located
the lens arrays in place, such that they could be viewed as a
on the physical display screen and another plane u coincides with
light field or glasses-free 3-D image after the fact. The main
the pupils of the viewer. To pass our Turing test for displays, i.e.,
drawback of parallax barriers and integral imaging is the spato create a sufficiently persuasive 3-D experience, a 4-D light
tioangular resolution tradeoff: adding more light field viewing
field display would have to provide appropriate stereoscopic,
zones comes at the cost of reduced spatial display resolution.
motion parallax, and focus cues. No such display exists today,
IEEE SIgnal ProcESSIng MagazInE

September 2016

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Table of Contents for the Digital Edition of Signal Processing - September 2016