Displays: basic LCD technology Basic LCD technology Basic LCD

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11/10/2016
Gianni Ramponi
http://www.units.it/ramponi
Gianni Ramponi
Digital Image Processing
Displays: basic LCD technology
LCs are mesophases between crystalline solids and isotropic liquids.
calamitic (=elongated) molecules are used in LCDs
Basic LCD technology
Longitudinally asymmetric (chyral) molecules can be used, which
organize themselves into cholesteric structures
4-n-pentyl-4-cyano-biphenyl
The aromatic biphenyl (C₆H₅)₂
component is the rigid core, the
hydrocarbon chain is the flexible tail.
The core favors both orientational
and positional order while the tail
does not. With balanced rigid and
flexible parts, the molecule exhibits
liquid crystal phase
To permit light propagation, a
suitable relationship must exist
between the direction of the
electric field of the light
(polarization) and the orientation
of the molecules
D.-K. Yang and S.-T. Wu,
Fundamentals of Liquid Crystal Devices,
© 2006 John Wiley & Sons
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D.-K. Yang and S.-T. Wu, Fundamentals of Liquid Crystal Devices, © 2006 John Wiley & Sons
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In a twisted nematic display the LC is anchored parallel to the cell
surface by the alignment layers. The total twist angle is 90 deg here.
When a sufficiently high electric field is applied across the cell, the
liquid crystal is tilted toward the field direction
Normalized transmittance
Temperature effects
• LCD's will recover from brief exposure to isotropic temperatures.
• Temperatures above +100º C damage the display's internal coatings.
• At low temperatures the display's response time increases due to the
fluid's increased viscosity.
• Change to crystalline state does not imply permanent damage.
Typ. threshold voltage vs. temperature of a TN fluid
Threshold increase
starts below ~15°
and is significant
(compare to voltage
values in the
transmittance curves
in previous slide)
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Due to optical anisotropy of liquid crystals and off-axis light leakage
from crossed polarizers, the contrast of a TN cell rapidly decreases in
the upper direction and in the lower diagonal directions. In the lower
direction the contrast remains high, but gray-scale inversion is
observed (not shown in figure).
Twisted nematic (TN),
thin-film-transistor (TFT)
technology
A pair of wide-view films can reduce the effect
Iso-contrastratio plots
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IPS - LCD technology
Equipotential lines
In-Plane-Switching
(normally black)
analysis
polarizer:
.
thinner display
reduced parallax error
input
polarizer:
• Note light is transmitted when V = on
• A problem with IPS: above the electrodes the electric field is
unable to twist the LC
the light transmittance is lower
http://www.merck-performance-materials.com/en/display/function_of_lcd_technologies/function_of_lcd_technologies.html
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FFS - LCD technology
Google: 3M lcd optics 101
Fringe-Field-Switching
here, the strip electrodes have the same electrical potential, so that they
can be placed close together. This in turn allows higher transmission,
since the area above the electrodes can also contribute to the switching
process.
and find detailed animated
info on lcd display structure
Source: Hitachi
analysis
polarizer:
.
input
polarizer:
http://www.merck-performance-materials.com/en/display/function_of_lcd_technologies/function_of_lcd_technologies.html
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iPhone 6+
5.5-inch (diagonal)
1920 x 1080
IPS
401 ppi
1300:1 contrast ratio
500 cd/m2 max
brightness
- LCD technology
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(Lu 2007)
Transflective IPS
- "2k"=2560x1440
displays available
- 4k displays to come (to
be used e.g. in VR
headsets)
A λ/4 filter [oriented at 45° it converts linear pol. to circular; then
viceversa, at further 45°] is traversed twice by both the back (1x 2
filters = 90°) and reflected light (2x 1 filter = 90°)
BUT the two added filters absorb light
without sunlight, the display
looks washed-out
needs stronger backlight
power consumption,
heat
http://www.edmundoptics.co.uk/resources/application-notes/optics/understanding-waveplates/
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Increased luminance
LED-illuminated LCD
- 2006: wVGA (800x480) 4.5-inch aSi prototype
-2008: scheduled production of
handheld consumer products
Samsung (see
- Clairvoyante
pentileblog.com)
- 2012: Samsung uses PenTile
(RGBG) AMOLED display
Isamu Akasaki, Hiroshi Amano
Nagoya University, Japan
Shuji Nakamura
Univ. of California, Santa Barbara, CA,
USA
Necessity of white point control
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LED-illuminated LCD
LEDs differ from
old gas discharge
lamps:
- can be switched
fast,
- are available in
all colors,
- small,
- environmentally
friendly (??),
- low voltage
“for the invention [1990] of
efficient blue light-emitting
diodes which has enabled
bright and energy-saving
white light sources"
LED-illuminated LCD
LED spectra
compared to
Cold Cathode
Fluorescent
Lamp + colour
filters
NOTE: thin
and strong
peaks at RGB
freqs. can be
obtained using
QUANTUM
DOT devices
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QD Vision provided Nexxus Lighting (NC)
Quantum dot displays
Note: «Triluminos» was already used by Sony
in 2007 for a different, short-lived technology
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Modulated LED + LC displays
(Seetzen 03)
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Seetzen 07
Seetzen 07
Trentacoste 06
Trentacoste 06
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Seetzen 07
Seetzen 07
Trentacoste 06
Trentacoste 06
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Various prototypes / professional market products:
- 1380 2.5Watt LEDs on a 18.8mm hexagonal closepacking matrix, each
LED individually controlled with 256 steps.
- The LCD panel is a 37 in Chi Mei Optoelectronics V370H1-L01, 250:1
simultaneous contrast ratio and 1920 × 1080 resolution.
- For a full white box occupying the center third of the screen, the
maximum luminance is measured as 4760 cd/m2.
- For a black image, the min. luminance is zero,
all LEDs are off. (Trentacoste 2007)
Seetzen 07
SIM2 (HDR47ES6MB)
• Dolby
2202 LEDs, 6000 (2300?) cd/m2,
ANSI contrast 20,000,
air-cooled
Trentacoste 06
• Dolby prototype 2014:
18,000 LEDs ?
http://hdr.sim2.it/hdrproducts/hdr47es6mb
http://hdr.sim2.it/node/39
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Dual-layer LCD
Dual-layer LCD
later: Barco
The front- and rearpolarizers of the two
panels must be properly
oriented!
- 8+8=16 bit images
- Tmax = 2 %
(14%*14%)
- Lmax/Lmin = 90,000
(300:1)*(300:1)
- Basic image
processing:
Y= Y Y
Source: Philips Research - FIMI
Source: Philips Research - FIMI
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Dual-layer LCD
see industrial LCD datasheet (Kyocera)
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Plasma technology
More…
(IEEE Spectrum 2010)
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IEEE ELECTRON DEVICE LETTERS, VOL. 33, NO. 4, APRIL 2012, P.543-5
IGZO (InGaZnO) TFT
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IGZO (InGaZnO) TFT
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IGZO (InGaZnO) TFT
Oxide semiconductor thin-film transistors (TFTs) have
attracted attention as leading devices for nextgeneration displays because of their transparency,
flexibility, high-speed operations, and larger sizes. These
features are not available simultaneously in existing
silicon-based TFTs. The current drivability of amorphous
silicon TFTs is insufficient for use in organic LED (OLED)
displays, and the poor uniformity of polycrystalline
silicon TFTs is a critical issue for large-size displays. Oxide
semiconductor TFTs are expected to overcome such
shortcomings. The crystalline structure of InGaZnO4 was
found in 1985. So far, amorphous IGZO has been mainly
investigated as a TFT channel material. However,
reliability issues such as degradation under temperature
stress have not been solved sufficiently.
13.5-inch flexible OLED using
CAAC IGZO TFT drivers
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A c-axis aligned crystal
(CAAC) film is closer to a
single crystal than an
amorphous material. It has caxis alignment like a single
crystal, but its a-b plane has a
mosaic pattern and no grain
boundaries. The CAAC differs
from a polycrystal, which
generally has a, b, and c axes
oriented at random and with
clear grain boundaries. Figure
shows plane and crosssectional
transmission
electron microscopy (TEM)
images of our thin film,
respectively.
The
crystal
structure in the film is
hexagonal when seen from
the c-axis. It has a layered
structure when seen from the
direction perpendicular to
the c-axis.
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CAAC IGZO TFT
Projectors: LCD
http://www.sharp-world.com/igzo/
Projectors: LCoS
Liquid Crystal on Silicon
(Sony: SXRD, Silicon X-tal Reflective Display)
• Polarization is managed by
splitters
no films on the LC
• Is traversed twice by light
can be thin
fast
• High aperture ratio
efficient
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Projectors: LCoS
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Projectors: Digital Light Processing
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Projectors: light sources
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By combining a
laser, a fluorescent
element and an LED
Casio has created
an original mercuryfree hybrid light
source
capable of
generating high
brightness. Casio
has achieved
high brightness
output of green
light, (difficult with
conventional
semiconductor
light sources), by
efficiently
converting blue
laser light into
green light using a
fluorescent element.
Projectors: light sources
Performances
Barco @ Laser Display Conference, Yokohama, 2013
* 60.000 lm (55.000 ANSI lumen) laser projector
* Free-space coupled laser source (i.e. no fiber coupling)
* Semiconductor lasers:
* blue and red are direct diodes
* green is frequency converted IR laser diode
* Wavelengths: 460 nm for blue, 532 nm for green and 637 nm for red.
Resulting colour gamut completely encompasses DCI colour gamut.
* Total optical laser power: about 600W.
* The power of the lasers is white balanced to standard DCI (D63) white
point, without the need for electronic color correction.
* Optical architecture: 1.38” 4K DMDs, color splitting prism.
* Low Speckle
[Interference always exists between light and object features
(optical fibers, screen) having size close to wavelength
Light is
sourced by a laser is coherent
highly correlated
spatially and
temporally stable interference
SPECKLE NOISE]
Display
LCD
plasma
luminance
nit (cd/m^2)
contrast
n:1
300 - 500
1000 - 1500
500 - 1000 ...
1000 - 10,000 ...
luminous flux
lumen (cd*steradians)
Projector
LCD
DLP
700 - 3000
1000 - 3000
500 - 1000
2000 - 4000
Comment:
“Display manufacturers often employ various methods of distorting the
calculation of dynamic range, such as altering room illumination between
measurements” (Trentacoste 2007)
... or mixing up static (spatial) and dynamic (temporal) contrast values
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Performances
White paper, direct sunlight:
White paper, outdoor, sunny:
Dark objects, outdoor, sunny:
Dark object, indoor, natural light:
LCD Display, indoor, white:
LCD Display, indoor, black:
LCD Display, indoor, off:
CRT Display, indoor, white:
CRT Display, indoor, off:
3-D
18900 cd/m^2
1630 cd/m^2
60-70 cd/m^2
1.6 cd/m^2
269 cd/m^2
1.92 cd/m^2
1.15 cd/m^2
59.3 cd/m^2
3.17 cd/m^2
DLP projector, dark indoor, white (100”): 57.9 cd/m^2
DLP projector, dark indoor, black:
0.05 cd/m^2
Projection screen, indoor, natural light
39.7 cd/m^2
-- Bad case dynamic range: (57.9+39.7) / (0.05+39.7) = 2.5
DLP projector, dark indoor, white (69'‘)
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183 cd/m^2
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Digital image fundamentals
State of the Art in Stereoscopic
and Autostereoscopic Displays
Hakan Urey, Senior Member IEEE, Kishore V. Chellappan ,
Erdem Erden, Student Member IEEE , and Phil Surman
Proceedings of the IEEE | Vol. 99, No. 4, April 2011
Displays_3D_Urey11.pdf
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The type of 2-D signal f(x,y) we deal with is represented by a real
function of two integer variables
f ( x, y ) = f ( xTx , yTy ) = f ( xa , ya ) | xa = xTx , ya = yTy
Data domain
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• A 2-D function is causal if f(x,y)=0 for x,y<0
It is semicausal if f(x,y)=0 for x<0, (x=0 and y<0)
• A 2-D system is
causal
or
semicausal
if the "previous" input data are located left/above the dashed lines
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Frequency domain
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The Moiré pattern is an
aliasing effect, often
visible on finely textured
regions.
In this case it takes the
form of a low-frequency
vertically running sinusoid
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Digital image fundamentals: dithering
Adding noise before the quantization can improve the
appearance of coarsely quantized images.
• The existence of pixels having amplitude close to the
threshold(s) is made apparent.
Note: the
binarization
threshold is
the same
See Matlab
• A randomized version of halftone printing. More visually
effective algorithms exist (Floyd-Steinberg, error diffusion)
• Sub-pixel dithering can be used to increase the graylevel
resolution in (medical) colour displays

Displays: basic LCD technology Basic LCD technology Basic LCD

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