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Display Panels

I will go with this guide from a semi-commercial and semi-technnical aspect.

Ok firstly I will solve the common misconception of LED being a new
technology in Panels.
LED is just an alternative display backlight technology which reduces power
consumption and makes the panel slimmer and improves colour
reproduction(The colour reproduction difference is not practically
noticeable and if you think that the colours are better its just
psychological and price-tag based).

This guide is not only for the monitors but also for the TVs since they are
basically same except for different input options.

*Common Input/Output Ports*
*Analog*

*1.VGA-Video Graphics Array*
Probably the most common Input and output ports.They have been used for a
long a time and are still used.Present in almost all the Computers(Desktop and Laptop),Monitors and
also Projector.They are also found in some TVs which make it
easier to connect your Computer to the TV.

*2.Video Component*
The most common port used in TVs.Everybody is prett familiar with it.Those
Yellow,Red and White cable are a called video
component cables.The yellow is for the video and the red and white are for
audio.Since most TVs have 2 speakers the red
and white provide separate inputs to both the speakers so the audio
experience can be more life like.They are basically a
component analog signal split in 3 components hence the name.

*Digital*
* **1.DVI-Digital Video Interface*
It is usually seen in the new monitors it is just a video input/output
interface.It is also seen on the new GPUs and is very
unusual in TVs but is seen in some Korean and chinese brand TVs which is
really helpful since makes connecting new computers to the TVs really easy.

*2.HDMI-High Definition Multimedia Interface*
* *This input is really hyped about a but basically what is does is reduce
the multiple wires and provides a video interface like
DVI and High Def upto 8 (usually 5)Channel audio interface with just 1 port
instead of using 1 DVI port and 3 3.5mm Jacks which will provide better audio output since it will also include a subwoofer which the HDMI does not because you need an
amplifier for that.But still it is pretty great reduces the cable management
and also convinient to install.
It can also be considered as all the components cables in one port but in
digital format.It is seen in most of the flat screen
TVs and some Multimedia Monitors but still the Professionals prefer the DVI
due to some misconceptions.
There are many comparisons amongst the interfaces and generic comparisons
between the analog and digital signals.
But there is no sureshot answer that the digital is better in quality than
analog.They both have their ups and downs.One might argue that the need
of a converter box may not be needed when playing video through a digital
connection that is true which makes the video unaltered but since all
the output must be scaled according to the monitor’s calibre(Resolution and
stuff) so it is eventually going through conversion so it will be altered
and also once the data is lost in a Digital Line it cannot be recovered.So
there are ups and downs for both kinds of inputs.
Depends on what you are using and what will be the best for that situation.
But still looking at the current market scenario it is better to use Digital
since the analog interfaces will be phased out soon.

Some panel technologies will be discussed from a Commercial-Technical
aspect.
I wont be going in to the detail of the pixel shading and the RGB
active-matrix transistors and stuff but still the following information will
help you in your buying and understanding of some basic things and also you wont be
fooled by any advertisement and will get the spoofs in the company advertisements.
Like why is the Sony Bravia X series more expensive from god knows which all
letters they use.
The two commonly used backlights
*1.CCFL*
*2.LED*
*
*
*1.CCFL -Cold Cathode Fluorescent Lamps*
*
*
*2.LED – Light Emitting Diode*
*

There are 3 types of Panel Technologies.
*1.TN – Twisted Nematic*
*2.VA – Vertical Alignment*
*3.IPS – In Plane Switching*
*
*
*1.TN-Twisted Nematic -*
.It is also the most commonly used technology in most of the LCD TV and
Computer Monitors. TN panels are the cheapest of the three

technologies to make. The main advantages of TN panels are their
fast–usually 2ms–response time and, of course, low price. Their major
disadvantages are narrow viewing angles, relatively low brightness, and
inaccurate color reproduction.

*2.VA -Vertical Alignment -*
Mostly seen as S-PVA panels. VAs have improved viewing angles compared with
TNs, better color reproduction, and they typically have a much
higher maximum brightness. Also, they tend to have the lowest black levels
of all three panel technologies. Unfortunately, a VA panel’s response
time and input lag are not quite as fast as a TN panel. Also, you can expect
a VA-based monitor’s profile to be wider than a TN’s.And they are more expensive than the TN but cheaper than IPS.Our College has one of these
that I know of .Its in the FOSS lab EnTC Exten. Building 3rd Floor.It is rigged to the really cool HP Opteron.

*3.IPS – In-Plane Switching* –
IPS-based monitors are usually the most expensive; however, the new e-IPS
panels are cheap for a 22″ model. They also have the best viewing
angles of all three technologies and produce the most accurate colors;
however, their blacks are not as deep VA panels. IPS monitors are the
slowest of the bunch in both response time and input lag.Hitachi was the
inventor of this technology and Sony rarely uses this technology.All the
Apple Computer are so expensive because they make the best displays.All of
them are IPS panels and to put a cherry on the top they all have
LED back lighting people do not consider that but since a normal user has
nothing to do with the panel technology they are using nobody cares
about the expensive iMaCs in India.But some TVs which are inexplainably
expensive are IPS panels and no one even cares about this spec and
what they see is that the same size TV can be bought at a 77% lower price.

*In a Nutshell*
*
*TN*
+ Lowest price
+ Fastest response time
– Inferior color reproduction
– Very narrow viewing angles

*VA*
+ Good viewing angles
+ Deep blacks
+ Medium price
– Color shifting on extreme angles
– Relatively slow response times

*IPS*
+ Good response times
+ Great color reproduction
– Expensive (e-IPS are more “medium price” however)
– Blacks not as deep as VA

Some basic Monitor specifications

*Aspect ratio*: Although some people contend 4:3 monitors are still best for
surfing the Web, the vast majority of monitors available for purchase
today have a width to height proportion (or aspect ratio) of 16:10, with
16:9 coming in at a very close second. For the last few years, with the
advent of wide-screen monitors, most screens have been of the 16:10 variety.
Starting in late 2008–and picking up steam in 2009–monitor
vendors have really been pushing out 16:9 monitors as fast as they can make
them.

This shift to 16:9–and by association to a 1080p (1,920×1,080 pixel)
resolution–aspect ratios stems from the industry’s desire for monitors to
become more like HDTVs, and this seems to be the direction the computer
monitor industry is headed right now. Companies will most likely still
release professional-grade monitors where precise colors are crucial, in the
16:10 aspect ratio, as there really is no good reason to change
ratios.

Still, today it comes down to 16:10 or 16:9 ratios. The difference between
the two ratios is most prevalent while watching movies. On a 16:10
monitor, you have a choice when watching a movie filmed in 1.85:1 aspect
ratio, such as on “Sin City.” You can either watch it letterboxed format
at its original 16:9 aspect ratio, or watch it in full screen with the image
stretched to fit the screen. On a 16:9 monitor you can watch the same movie
in full screen with no stretching.

Movies shot in 2.35:1 (like “Iron Man”) are always letterboxed, whether on
16:9 or 16:10 monitors unless you zoom the image.

Essentially, a 16:9 monitor can display a full-screen 16:9 Blu-ray or
digital movie shot in 1.85:1 without stretching the image to fit the screen.
A 16:10 monitor will need to stretch the same movie’s image a bit to get it to
full screen without any black bars.

*Black Level: *No display can show black without some light seeping through.
Black level is a measurement of how much light emanates from the
display while showing black.

Brightness: A measurement of how much light a panel can produce. Luminance
is expressed in candelas per square meter (cd/m2). A measurement of 200 to 250 cd/m2) is OK for most productivity tasks; 300 to 400 cd/m2 is great for movies and games.

Contrast ratio: The difference in light intensity between the brightest
white and the deepest black.
While contrast ratios typically don’t exceed 1,000:1 on monitors; lately,
manufactures have been pushing Dynamic Contrast as a spec, and
sometimes misleadingly calling it contrast ratio.

Before a monitor is released to the public, panels go through testing in the
vendor’s own lab. These tests produce the specs that the vendor will
then publish with the release of the monitor. Specs such as maximum
brightness, pixel pitch, pixel response time, contrast ratio, and dynamic
contrast ratio are all determined in the vendor’s lab.

When testing normal contrast ratio, vendors use a device that measures
luminance to determine how much light is emanating from a display while
it’s showing both a completely black and a completely white screen. They
then take each number, do a bit of math, and come up with the contrast
ratio.

Now, aside from a relatively low number of LCDs that use LED-backlighting
technology, all LCDs have a lamp built in to their screens. When you
turn your brightness setting down, you’re actually just dimming the lamp in
the back. When the vendors dim the backlight to get the contrast ratio
score, they dim it to a point, but do not turn it off.

When they test to get the readings for Dynamic Contrast, however, they turn
off the backlight.

With the backlight off, the darkness of the black level increases by a
factor of 10 or more. At this point, the vendor takes its reading for the
dark screen and compares it with the white screen reading it recorded earlier.
Since this new dark screen level is so dark, it increases the contrast
ratio. The problem is that the screen only gets this dark when the video
signal is black or near black–not very useful when you’re watching a
movie, or playing a game, or doing pretty much anything. The primary reason
for including this feature is that the contrast ratio goes from 1,000:1
to 10,000:1, and even 30,000:1.

When vendors push Dynamic Contrast as a spec for LCDs that use
LED-backlighting technology, however, it may be more appropriate. Direct
contrast ratio works differently with LEDs than with lamp-based LCDs. When a
portion of an image in a movie is relatively dark, the LEDs in that
local area of the screen are dimmed. This occurs on a frame-by-frame basis
and lowers the black level in that dark area only. Unfortunately, this
implementation has its weaknesses, as well, as there can be some noticeable
visual glitches in the areas that darken.

Bottom line? Take all measured specs with a grain of salt; however, take
Dynamic Contrast specs with a huge bucket load of salt.

*DisplayPort:* Heralded as the successor to DVI and HDMI, DisplayPort is a
higher bandwidth connection that could facilitate thinner and lighter
monitors as they would no longer require special circuitry (and hardware to
run that circuitry) to receive video signal. Adoption of this technology
has been sparse, to say the least.

– Mihir Khatwani ( S.Y. Comp)

Categories: Technical
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  1. May 22, 2014 at 8:11 pm

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