NEC Flat Panel Television LCD2180WG LED User Manual

NEC LCD2180WG-LED

Technical Background and Feature Overview

NEC Display Solutions

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Color Gamut of a Display

The size and position of the triangle are de-

termined by the purity of the primary colors.

The purer the color, the closer it is to the edge

of the CIE horseshoe. Colors along the edge of

the horseshoe are made up of pure monochro-

matic light.

Color displays are additive color devices. Color

is formed by adding different proportions of

red, green and blue light. These primary colors

are formed by the glow of different types of

phosphors in the case of a CRT display, or by

filtering white light into red, green and blue

on an LCD.

When a light source is viewed as a spectrum, it

is possible to see the relationship between it’s

spectrum and position on the CIE color chart.

Red + Green = Yellow

Green + Blue = Cyan

Blue + Red = Magenta

Red + Green + Blue = White

400

600

700

500

Light Wavelength (nm)

Monochromatic Light lies along the

edge of the CIE horseshoe

The color gamut of a display is limited by how

pure in color the red, green and blue primaries

are.

When viewed on a CIE xy color chart (a 2

dimensional plot of all colors visible to the hu-

man eye), the red, green, and blue primary col-

ors together form a triangle. Colors outside

of this triangle are outside of the displayable

color gamut.

400

600

700

500

The largest possible color gamut using 3 colors

would be obtained by using 3 monochromatic

light sources such as LASERs.

Light Wavelength (nm)

Light made up of a broader spectrum

lies inside the CIE horseshoe.

Typical LCD monitors use a broad-band light

source such as CCFLs, which radiate a wide

spectrum of colors, including unwanted colors

The LCD2180WG-LED avoids the need for narrower

spectrum color filters by fundamentally changing

the spectrum of the backlight source. By using

LCD Operation and Color Gamut

With an LCD display, the color gamut is deter-

mined by a combination of the light source

used to illuminate the LCD panel(known as the

backlight) and of the LCD panel itself.

such as oranges, yellows, cyans. Only the pure red, red, green and blue power LEDs, which output

green and blue parts of the backlight spectrum

are wanted in order to maximize the color gamut

of the display.

a very narrow spectrum of light, a huge gain in

displayable color gamut can be achieved without

the need for using narrower color filters on each

sub-pixel.

It is important to understand that the backlight

for the LED based display is still “white” light,

but it is made up of very narrow-band red, green

and blue light, which when combined together, is

perceived by the human eye as white light. If this

light were to be shown as a rainbow spectrum us-

ing a prism, only the red, green and blue portions

of the rainbow would be seen.

400

600

700

500

LCD Screen Sub-Pixel Structure

Light Wavelength (nm)

Typical CCFL Backlight Spectrum

Each pixel on the screen is made up of red, green

and blue sub-pixels. The colors of these sub-pix-

els are made by passing the backlight through

a color filter array. The characteristics of these

color filters in part determine the gamut of the

display.

In order to achieve a larger color gamut, it would

be necessary to filter the backlight into a nar-

rower spectrum of colors thus producing purer

red, green and blue. However, filtering into a nar-

rower spectrum is a technological challenge and

doing so also reduces the total amount of light

that is transmitted through the filter. This means

that the overall screen luminance is reduced or

must be compensated for by using more CCFL

backlights.

Backlight

TFT Array

Liquid Crystal

Color Filter Array

400

600

700

500

Light Wavelength (nm)

Combined LED Backlight Spectrum

LCD Color Filter Array

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The LCD2180WG-LED display further increases the

displayable color gamut by using a custom modi-

fied color filter on the blue sub-pixels reducing

the amount of cyan that passes through. This has

the effect of increasing the blue gamut beyond

that which is achievable using a blue LED and

standard blue filter.

AdobeRGB and beyond

Many mainstream output devices

such as ink jet printers can now pro-

duce colors that lie outside of even

the AdobeRGB colorspace.

The gamut of LCD2180WG-LED

exceeds AdobeRGB in the red and

magenta areas, making it possible to

view colors beyond AdobeRGB.

See diagram on page 9 for a more detailed expla-

nation of how the wide color gamut is achieved

and how it compares to a typical CCFL display.

The LCD2180WG-LED display complies

with the new AdobeRGB(1998) Refer-

ence Viewing Environment specifi-

cation. A preset for matching the

AdobeRGB color gamut is available

via the On Screen Display menu.

LED Backlight

The backlight source for the display is a linear

array of 48 individual red(18), green(20) and blue

(10) power LEDs. The light from these LEDs is

combined together to form white light, which is

the backlight source for the LCD panel.

increased intensity of the display makes direct

comparisons a reality.

Display Lifetime

Commercial LEDs have been around since the

early 1960s, however it is only within the last 10

years that blue LEDs have become available, and

only within the last couple of years that ultra

high brightness LEDs capable of replacing CCFLs

have become available with a comparable power

consumption. One of the major benefits of LEDs,

besides the narrow output spectrum, is the long

lifetime of typically 50,000 hours. This compares

to a typical CCFL based display lifetime of 25,000

hours.

Red, Green and Blue LED Array

Each LED that is used in the LCD2180WG-LED

display is individually chosen using a rigorous

screening process for color spectrum and lumi-

nance output in order to achieve the maximum

possible color gamut and color uniformity across

the display screen. Only a very small fraction

of the LEDs produced by the manufacturer are

deemed acceptable and chosen for use in the

display.

Display White Point

The intensity of the red, green and blue LEDs

can be individually controlled, allowing the white

point or color temperature of the resulting white

light to be adjusted. This represents a major ad-

vantage over traditional LCD displays that utilize

a CCFL backlight with a fixed color temperature.

Folded Light Guide Design

In order to allow the light from the individual red,

green and blue LEDs to mix together and appear

as a single white light source, the display features

a folded light guide design. Light from the row

of alternating colored LEDs is fed through a

light guide and curved mirrors at the rear of the

display.

Folded Light Guide and LED Array

In a traditional LCD display, the only way to

adjust the white point of the screen is by using

a look-up-table, which resides either in the host

computer’s video graphics adapter or internally

to the display itself.

Luminance

When compared to CRT monitors, the high bright-

ness of the power LED backlight allows for a much

higher screen intensity(brightness) to be used.

A typical intensity of 160 cd/m², regardless of the

white point setting, allows the display to be used

where traditionally a darkened room was neces-

sary. Also where direct side-by-side comparisons

with print samples in a light box were previously

difficult due to the difference in luminance, the

This allows the light from the individual LEDs a

greater distance in which to mix together, thus

giving a much more uniform light source without

significantly increasing the depth of the display.

Changing the white point from the display’s

native white point means that one or two colors

have to be reduced in luminance using the look-

up-table. This means that fewer displayable colors

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are possible due to the look-up-table being used

to compensate for the white point. Depending on

the display’s native white point and the desired

white point, a significant number of display-

able colors may be lost leading to color banding

issues. This is especially true for displays that

do not feature programmable internal look-up-

tables with a depth of 10 bits or more.

Additionally, with traditional LCD displays, the na-

tive white point of the backlight source is fixed,

and the white point is adjusted using look-up-

tables. Therefore, the greyscale color tracking

of the display is often poor, especially for very

dark colors. This is because for very dark colors

including black, no color corrections are possible

using the look-up-table. The color of black on the

screen will be the color of the backlight source

that leaks through the LCD panel, which may dif-

fer from the desired white point.

Another advantage of the LED Backlight is that

the contrast ratio of the display remains almost

constant as the white point is changed in inten-

sity and color. This is because the intensity and

color of black will also change due to the entire

backlight source being adjusted, rather than

having a fixed backlight and LUT adjustment with

a typical LCD display.

Gamut Mapping/Emulation

While the native color gamut of the display

exceeds that of even AdobeRGB, it is sometimes

necessary to preview images as they would be

seen on a display with a smaller colorspace.

The LCD2180WG-LED has presets for emulating

displays with both sRGB and AdobeRGB gamuts

by using internal color gamut mapping. These

presets can be selected with the touch of a but-

ton and will transform the displayed image into

either sRGB or AdobeRGB gamuts.

LED Backlight monitor

CCFL Backlight monitor

LUT Input

Typical CCFL Display LUT

However with the LCD2180WG-LED display, the

white point is adjusted by directly varying the

brightness of the red, green and blue LEDs. This

means that the full range of the internal 10

bit look-up-tables is available for performing

response curve and gamma adjustments.

Delta-E

Typical Color Tracking

With the LED backlight, the white point of the

entire backlight source is changed by varying the

intensity of the red, green and blue LEDs. So the

color of absolute black on the screen will be much

closer to the intended white point. This provides

vastly improved greyscale color tracking.

LUT Input

OmniColor Hue & Saturation Adjustment

Typical LED Display LUT

HOST COMPUTER

LCD2180WG-LED DISPLAY MONITOR

10 Bit Look Up Tables

Since the LCD2180WG-LED has internal 10 bit Look Up

Tables(LUTs), that can be programmed by the calibration

software, the 8x8 bit LUT on the Host Computer can be

set to linear. This means that no steps are lost in an 8x8

LUT and subsequent 8 bit DVI bottleneck(assuming 10

bit DVI functionality is not used).

8 bit x 3 colors

Frame Buffer

8 bit in x 8 bit out

x 3 colors LUT

(Set to Linear)

8 bits in x 10 bits out

x 3 colors LUT

LCD Panel

with LED Backlight

8 bit DVI

DDC/CI Adjustment

Also, since the white point of the display is controlled

directly by varying the intensity of the Red, Green and

Blue LEDs, the 10 bit LUTs in the display are only used

for gamma/tone response curve corrections. This pre-

serves the maximum number of discrete color levels.

HOST COMPUTER

TYPICAL CCFL DISPLAY MONITOR

8 bit x 3 colors

Frame Buffer

8 bit in x 8 bit out

x 3 colors LUT

8 bits in x 8 bits out

x 3 colors LUT

LCD Panel

with CCFL Backlight

8 bit DVI

On a traditional CCFL display monitor, the 8x8 LUT on the

host computer is used for both white point and gamma

/tone response curve corrections. This means a loss in

the total number of discrete color levels which can lead

to color banding issues.

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If necessary, custom gamuts can be achieved by

manual adjustment of the display using its ad-

vanced 6-axis color hue and saturation controls.

While other CCFL based LCD displays may claim to

have similar optical feedback systems, they typi-

cally only monitor the luminance of the backlight

source and not its true white point. CCFLs have

an operating temperature vs output color spec-

trum dependency which can produce a change in

the white point of the display as it warms up to

operating temperature; even if the overall lumi-

nance is compensated using a luminance based

optical feedback system.

called ColorComp which aims to reduce any

screen uniformity errors to almost unnoticeable

levels. This system works by applying a digital cor-

rection to each pixel on the screen to compen-

sate for differences in color and luminance.

These controls allow the hue and saturation of

red, yellow, green, cyan, blue and magenta areas

of the color gamut to be manipulated indepen-

dently.

Each display is individually characterized during

production using a fully automated system which

measures hundreds of points across the screen

at different grey levels. These measurements

are used to build a three dimensional correc-

tion matrix for the display screen which is then

stored inside the display. This data is used to

compensate for the screen uniformity, not only as

a function of position on the display screen, but

also as a function of grey level.

Color Stability

While LEDs have excellent light output and

lifetime characteristics, they are inherently

unstable devices and have very strong tempera-

ture and supply current dependencies. This would

normally make LEDs unsuitable for color critical

applications where a change in luminance of just

a fraction of a percentage would produce an

unacceptable color or luminance shift.

LED Backlight monitor

CCFL Backlight monitor

If desired, the ColorComp correction can be

turned off in order to maximize the screen

brightness.

Time after power on (minutes)

+85˚

+25˚C

-20˚C

Color Stability Comparison

Uncompensated Light Output vs Temperature

Temperature Compensation

Therefore the LCD2180WG-LED display employs a

unique internal optical feedback system which

constantly measures both the luminance and

color of the LED backlight source and automati-

The LCD2180WG-LED features a unique tem-

perature compensation system that constantly

monitors the internal temperature of the display

and corrects for changes in the LCD panel color

cally corrects for any short or long term changes. characteristics due to temperature shifts as

This means that the backlight source is constant well as changes in the sensitivity of the internal

and the screen can be used for critical color work optical feedback sensor. This compensation allows

Example Uniformity Without Correction

within a couple of minutes of powering on the

display. Short term changes such as the display

warming up, and longer term changes such as

aging decreasing the efficiency of the LED, are

automatically compensated for.

the display to achieve an unparalleled level of

color stability even as it warms up to full operat-

ing temperature. This means that the display

can then be used for color critical work within a

couple of minutes of turning on, compared to up

to 30-60 minutes for conventional displays.

Temperature

Sensor

Mura Compensation

All display monitors have some form of screen

uniformity errors, or mura, across the display

area due to a combination of non-uniformities

in the LCD panel itself, and the LCD backlight

system. This non-uniformity can be seen as

combination of shifts in color and/or luminance,

which, depending on the severity, may be very

noticeable and appear as uneven areas of color

across the display.

Folded Light Guide and LCD Panel

Color

Sensor

LED Array

Uniformity With ColorComp Correction

LED Power Driver

Dual Video Inputs

Microprocessor

The LCD2180WG-LED has two DVI video inputs for

connecting to two different host computers. The

input can be switched with the touch of a button.

The LCD2180WG-LED introduces a new screen

uniformity compensation and correction system

Optical Feedback System

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The need for 10 bit color depth

Normal color gamut display showing

available discrete colors with 8 bit

video (number of colors reduced for

purposes of explanation)

The increased color gamut of the display means that the

overall color “volume” of displayable colors has increased

significantly. However the number of discrete color levels

from the host system has not changed from the standard

16+ million colors, unless video graphics adapters, ap-

plications and Operating Systems, that all support 10 bit

graphic processing are used.

This means that there are fewer discrete displayable color

levels per unit of color volume on a wide gamut display

than on a standard gamut display, which can lead to color

banding issues.

The same number of discrete colors

on a wide color gamut display occupy

a larger volume.

Due to the LCD2180WG-LED being able to use the red, green

and blue LED intensity to adjust the white point, rather

than sacrificing displayable color levels using look-up-ta-

bles, this loss does not present a significant problem. How-

ever the display will be able to take advantage of future

generations of video graphics adapters, applications and

Operating Systems that are capable of outputting video

with the full 10 bit digital video depth that the display is

capable of accepting, thus providing an end-to-end color

palette of up to more than 1,000,000,000 displayable

colors.

When 10 bit video is used instead of 8

bit, up to ꢂꢀ times as many discrete

colors are available.

using a special spatial algorithm that ensures

The SpectraView_IIsoftware communicates with

the display directly using Display Data Channel

- Command Interface(DDC/CI), which is a two-way

communications link between the video graph-

ics adapter and display monitor that uses the

standard video signal cable. No extra cables are

necessary. All adjustments to monitor settings

10 Bit Interface

that adjacent pixels operate at different parts

of the Frame Rate Control cycle thus making

any artifacts of the Frame Rate Control process

imperceptible.

The LCD2180WG-LED features a video input that

supports 10 bit digital video using a single Dual-

Link DVI cable. This means that the full capabili-

ties of the 10 bit display can be realized without

being restricted to an 8 bit video input source.

Passive Cooling

The power LEDs used in the display dissipate heat are performed automatically using this commu-

While there are not currently any mainstream

video graphics adapters or operating systems

that support full 10 bit video processing and

output, the LCD2180WG-LED display is designed

for future compatibility and leads the way to the

time when 10 bit video will become mainstream.

during operation. The display uses a combination

of a large heat sink with convection cooling to

maintain the temperature of the display. This

nications link.

The LCD2180WG-LED features three internal 10

eliminates the need for a cooling fan which would bit LUTs(one for each color) that are programmed

introduce acoustic noise.

directly by SpectraView_IIvia DDC/CI. These tables

allow very precise adjustments to be made to the

display’s Tone Response Curve without signifi-

cantly reducing the number of displayable colors.

Because all of the Tone Response Curve adjust-

ments are done in a 10 bit domain within the

display itself, the host computer’s video graphics

adapter’s LUTs are set to linear, thus maximizing

the use of the 16+ million color palette in an 8 bit

color system.

Mercury Free Design

Advanced FRC

Unlike CCFL backlight based displays, which con-

tain mercury vapor inside the florescent lamps,

thereby restricting the usage in certain operat-

ing environments, the LCD2180WG-LED display is

mercury free and RoHS compliant.

The LCD panel on the LCD2180WG-LED display

achieves an effective output of 10 bits per color

by using an advanced Frame Rate Control dither-

ing algorithm. As with other 10 bit color displays,

the panel supports the most significant 8 bits

of video directly and the 2 least significant bits

are displayed by using a time-domain dither-

ing method known as Frame Rate Control, in

which pixels are changed in intensity according

to the level of the 2 lower bits at a rate that is

faster than the human eye can perceive. This

time-domain dithering is further enhanced by

Color Calibration

The optional SpectraView_IIcolor calibration

package offers further enhancements by provid-

ing a wide array of functions and features for

calibrating, profiling and monitoring the status

of the display.

The software allows custom target calibrations

to be created with preset or user definable white

points, intensity levels and tone response curves

(gamma curves). Advanced tone response curves

ꢃ

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such as DICOM, used for medical imaging, are also

available.

Once SpectraView_IIhas calibrated the display, the

OSD(On Screen Display) controls can be locked to

prevent accidental or unauthorized adjustment

which may invalidate the calibrated state of the

monitor.

Color Measurement

The output color spectrum of the LCD2180WG-

LED display presents a unique challenge to

the current generation of colorimeter devices

which were never designed to be used on such

a display, just as LCD displays were a challenge

to colorimeters that were only designed for

CRT displays.

The software features a Colorimeter function

which allows direct measurements to be taken

by the color sensor and the results displayed in a

variety of different formats.

To overcome this, the optional SpectraView_II

color calibration package for the LCD2180WG-

LED display includes a custom calibrated

Gretag iOne Display V2 colorimeter that has

been specifically calibrated for accurate

measurement of the display. The device can

continue to be used to measure standard LCD

displays as well, if a multi-monitor configura-

tion is used.

The SpectraView_IIsoftware integrates with the

NEC NaViSet Administrator network software

(Available separately from your NEC representa-

tive. Windows platform only) to provide remote

network access and monitoring of display

monitors. NaViSet Administrator is able to read,

display, and log the current calibration settings

and status of displays on a LAN. This feature is

particularly useful for large installations where

central monitoring and asset management is

needed.

Calibration Target Configuration

At the end of each monitor calibration proce-

dure, the display is automatically profiled and

highly accurate ICC/ColorSync color profiles are

generated and automatically registered with the

Color Management System. These profiles use the

Bradford Chromaticity Adaptation matrix.

NEC is actively working with manufacturers of

colorimeter devices to ensure that their fu-

ture standard products are able to accurately

measure the color characteristics of wide

color gamut displays.

Target and actual measured results are analyzed

and displayed, showing a wealth of information

about the display such as the measured color

gamut, greyscale color tracking, Delta-E, and lu-

minance values. Additional information about the

display monitor such as the model name, serial

Workﬂow Challenges With

Wide Color Gamut Displays

The use of a wide color gamut display is not with-

out its challenges. Many people who have used

While the LCD2180WG-LED ships with color profiles

for the factory preset color settings, the use of

a color calibration package is normally essential

for accurate custom calibration and profiling of

the display.

number and the total number of hours that it has a wide gamut display have come to realize that

been in use are also displayed.

while it is now possible to display colors that were

otherwise unable to be previewed on-screen,

challenges in other areas emerge.

For example, with being able to see colors on the

screen that were never before possible to display,

it is now easy to see problem areas in other parts

of the color workflow such as deficiencies in

printer or separation profiles.

The issue of having to continue to use some

legacy standard color gamut displays and

un-tagged source images in a color workflow is

another challenge.

Calibration Results Summary

Also it now becomes essential to utilize a color

management system with the display, by the cor-

rect use of ICC/ColorSync display profiles. Without

the use of a color management system, all colors

are mapped to the larger color gamut of the

display. This results in images that appear to be

super-saturated and distorted in color.

Sample Image

Accurate color profiles of the display allow the

color management system to correctly map the

source image gamut into the color gamut of the

display.

Color Tracking Report

Image Displayed Without Color Management

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