before you buy an lcd

8/6/2019 Before You Buy an LCD

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Before You Buy an LCD TV

Flat panel televisions are quickly becoming quite commonplace on store shelves and in consumers'homes. LCD flat panel televisions, with their decreasing price points and performanceimprovements are becoming a very desirable alternative to the standard CRT set. However, beforeyou jump at the latest "great ad deal" on an LCD flat panel television, there are some useful tips to

take into consideration.

1. Find a place to put your LCD TV

Since LCD TVs are very thin, they can be either wall or table mounted. For a wall mounted LCD TV,avoid placing over a functioning fireplace. The heat from the fireplace may affect the performance

and longevity of the set. If you are using the provided table mount, take a tape measure to thedealer with you so you can make sure that the entire width of the set will fit in your space. Makesure you leave one or two inches on each side, the top, and back, for ventilation and connectionaccess.

y What is an LCD TV?

y Answer: An LCD TV is a flat panel television that utilizes the same basic Liquid Crystal Displcell phones, camcorder viewfinders, and computer monitors.

y LCD panels are made of two layers of a glass-like material, which are polarized, and are "glu

special polymer that holds the individual liquid crystals. Electric current is then passed throuor block light to create images.

y LCD crystals do not produce their own light, so an external light source, such as florescent oLCD to become visible to the viewer.

y Unlike standard CRT and Plasma televisions, there are no phosphors that light up, and, thusoperate. Because of the nature of LCD technology, there is no radiation emitted from the sc

y Unlike a traditional CRT televisions, the images on an LCD TV are not "scanned" by an electrturned off or on at a specific refresh rate. In other words, the entire image is displayed (or rof a second. For more specifics on what refresh rate is and how it works, check out my articl

y However, LCDs do not produce there own light. In order for an LCD TV to produce a visible ihappens is that the pixels are rapidly turned on and off depending on the requirements of tbacklight through, when they are on, they let the backlight through. For a more technical loWorks (How StuffWorks).

y Also, without the need for a picture tube, LCD TV can be made very thin, thus allowing them

a table, desk, dresser, or cabinet very easily.y Combining the above technology with the features of a traditional television, such as, AV inp

loudspeakers, TV tuner, and traditional television adjustment controls, bring to life a conceptheater viewing.

y What is the Difference Between an LCD TV and a Plasma TV?Answer: Outward appearances are definitely deceiving when it comes to LCD and Plasmatelevisions. Although both types of televisions are flat and thin, they employ differenttechnology in an attempt to deliver similar results.Plasma TV Overview

Plasma television technology is based loosely on the fluorescent light bulb. The display itselfconsists of cells. Within each cell two glass panels are separated by a narrow gap in whichneon-xenon gas is injected and sealed in plasma form during the manufacturing process. The

gas is electrically charged at specific intervals when the Plasma set is in use. The charged gasthen strikes red, green, and blue phosphors, thus creating a television image. Each group ofred, green, and blue phosphors is called a pixel (picture element).Although Plasma television technology eliminate the need for the bulky picture tube andelectron beam scanning of traditional televisions, because it still employs the burning ofphosphors to generate an image, Plasma televisions still suffer from some of the drawbacks oftraditional televisions, such as heat generation and screen-burn of static images.LCD TV OverviewLCD TVs, on the other hand, use a different technology (see also question #1 for this same

explanation).Basically, LCD panels are made of two layers of transparent material, which are polarized, andare "glued" together. One of the layers is coated with a special polymer that holds the individualliquid crystals. Current is then passed through individual crystals, which allow the crystals topass or block light to create images. LCD crystals do not produce their own light, so an external


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light source, such as florescent bulb is needed for the image created by the LCD to becomevisible to the viewer.Unlike standard CRT and Plasma televisions, since there are no phosphors that light up, lesspower is needed for operation and the light source in an LCD TV generates less heat than aPlasma or traditional television. Also, because of the nature of LCD technology, there is noradiation emitted from the screen itself.Plasma vs LCD

The ADVANTAGES of Plasma over LCD are:1. Larger screen size availability.2. Better contrast ratio and ability to render deeper blacks.3. Better color accuracy and saturation.4. Better motion tracking (little or no motion lag in fast moving images).The DISADVANTAGES of Plasma vs LCD include:1. Plasma TVs are more susceptible to burn-in of static images. However, this problem hasdiminished greatly in recent years as a result of the incorporation "pixel orbiting" and related

technologies.2. Plasma TVs generate more heat than LCDs, due to the need to light of phosphors to createthe images.3. Does not perform as well at higher altitudes.

4. Potentially shorter display life span - this used to be the case. Early Plasmas had 30,000hours or 8 hrs of viewing a day for 9 years, which was less than LCD. However, screen life spanhas now improved and 60,000 hour life span rating are now common, with some sets rated ashigh as 100,000 hours, due to technology improvements.LCD television ADVANTAGES over Plasma include:1. No burn-in of static images.2. Cooler running temperature.

3. No high altitude use issues.4. Increased image brightness over Plasma, which makes LCD TVs better for viewing in brightlylit rooms.5. Lighter weight (when comparing same screen sizes) than Plasma counterparts.6. Longer display life used to be a factor, but now LCD and Plasma sets both have at least60,000 hour or higher lifespans.DISADVANTAGES of LCD vs Plasma televisions include:1. Lower contrast ratio, not as good rendering deep blacks, although the increasing

incorporation ofLED backlighting has narrowed this gap.2. Not as good at tracking motion (fast moving objects may exhibit lag artifacts) - However,

this is improving with the recent implementation of120Hz screen refresh rates and 240Hzprocessing in higher-end LCD sets.3. Not as common in large screen sizes above 42-inches as Plasma. However, the number is

growing fast, with 46 and 47-inch screen sizes becoming more common, and some LCD setshaving a screen size as large as 65-inches also available to the general public.

4. Although LCD televisions do not suffer from burn-in susceptibility, it is possible thatindividual pixels on an LCD televisions can burn out, causing small, visible, black or white dotsto appear on the screen. Individual pixels cannot be repaired, the whole screen would need tobe replaced at that point, if the individual pixel burnout becomes annoying to you.

5. LCD televisions are typically more expensive than equivalent-sized Plasma televisions(although this is changing).

2. Native Pixel ResolutionLCD flat panel sets have a fixed number of pixels on the screen surface. The key is to get as high anative pixel count as possible. Most LCD TVs 23-inches and up in screen size offer at least a1280x720 (720p) or 1366x768 (768p) native pixel resolution. These are the minimum pixel countsyou should look for in an LCD television.

In addition, most larger screen LCD TVs (especially those 40-inches and larger) now offer

1920x1080 (1080p) native pixel resolution, which is even more desirable, especially if you have,or plan to purchase a Blu-ray Disc player.

y Are All LCD TVs Also HDTVs?Answer: Almost all LCD TV are HDTVs. However, some of the smaller screen sets may not be. Thefollowing is an explanation on how to determine this.In order for any Television to be classified as an HDTV, the television must be able to display avertical resolution of at least 720 lines, represented as a 1280x720 pixel field (1280 pixels across

the screen and 720 pixels down the screen). Some smaller LCD TVs sets are referred to as EDTVs(Extended or Enhanced Definition televisions) as they only display a resolution lower than that of720 lines.EDTVs typically have a native pixel resolution of 852x480 or less. 852x480 represents 852 pixelsacross (left to right) and 480 pixels down (top to bottom) on the screen surface. The 480 pixelsdown also represent the number of lines from the top to the bottom of the screen. This is higher


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than standard television, but not HDTV resolution.The images on these sets can look good, especially for DVDs and standard digital cable, but it isnot HDTV. LCD TVs that are capable of displaying HDTV signals directly have a native pixelresolution of 1280x720 (where 720 also represents the number of lines from the top to bottom ofthe screen) or higher.Since LCD televisions have a finite number of pixels (referred to as a fixed-pixel display), signalinputs that have higher resolutions must be scaled to fit the pixel field count of the particular LCD

display. For example, a typical HDTV input format of 1080i needs a native display of 1920x1080pixels for a one-to-one point display of the HDTV image. Also, since LCD Television only displayprogressively scanned images, 1080i source signals are always either deinterlaced to 1080p orscaled down to 768p, 720p, or 480p depending on the native pixel resolution of the specific LCDtelevision.In other words, there is no such thing as a 1080i LCD TV. LCD TVs can only display video in aprogressive scan format, so if your LCD TV accepts a 1080i input resolution signal, the LCD TV hasto deinterlace and rescale the 1080i input signal to either 720p/768p on TVs with a 1366x768

native pixel resolution or 1080p on LCD TVs with a 1920x1080 native pixel resolution.Also, if your LCD television only has a pixel field of 852x480 or 1024x768, the original HDTV signalmust be scaled to fit the 852x480 or 1024x768 pixel count on LCD screen surface. HDTV signalinputs have to be scaled down to fit the LCD Television's native pixel field.

In conclusion, when shopping for a LCD Television, make sure you check to see if it is an EDTV oran HDTV. Currently, just about all LCD Televisions, 23-inches and larger, are indeed HDTVs, withmost having a 1280x720 (720p), 1366x768 (768p), or 1920x1080 (1080p) native pixel resolution,but some of the smaller (20-inch and less) units may not be.

y Definition of the Term: HDTV

Definition: HDTV stands for High Definition Television. HDTV refers to both a series of broadcaststandards approved by the FCC for consumer use and the high definition television hardwareneeded to display HDTV images.The two main standards used in HDTV broadcasting are:

720p (720 lines of resolution scanned progressively) is one of the HDTV standards. As such, ABCand FOX, have committed to 720p as their HDTV broadcasting standard. 720p provides a verysmooth, film-like image due to its progressive scan formula. Also, even though 720p is considered

high-definition, it takes up less bandwidth than 1080i, which is covered next.1080i (1,080 lines of resolution scanned in alternate fields consisting of 540 lines each) is the mostcommonly used HDTV format, and has been adopted by PBS, NBC, and CBS (as well as satelliteprogrammers HDNet, Showtime, and HBO through special feeds) as their HDTV broadcaststandard.In addition, 1080p, in which 1,080 lines of resolution are scanned progressively, is also in use,providing the most detailed high definition video image that is currently available.However, since 1080p is not a part of the FCC's approved over-the-air HDTV broadcast standards,

for that programming, it is displayed as a result of on-board video processing in a 1080p capableTV or Video Projector.In order to receive or display HDTV signals, you must have an HDTV.Also Known As: High Definition Television, High Def TV, HD Television, High Definition TV

y Definition of the Term: Pixel Density

Definition: Pixel Density is the actual amount of physical picture elements on a screen surface oran LCD/DLP projection chip. LCD/DLP projectors have a fixed number of pixels on their chips. Withreference to Video, the higher the native pixel count, the higher the resolution capability of thevideo display device. A native pixel count of 1024x768 (1,024 pixels across vs 768 pixels down) issufficient for DVD. However, 720p HDTV signals require a 1280x720 pixel count to give you a one-for-one signal representation, while a 1080i HDTV input signal needs a native pixel count of

1920x1080 for a one-for-one representation of the 1080i signal.Also Known As: Native Pixel Resolution, Native Screen Resolution, Screen Resolution

Scaling

Scaling is a process where a television's video processor will match the resolution of the incomingsignal to its native pixel resolution. This means that lower resolution signals will be upscaled, butthe processor will downscale higher resolution signals so that they can be displayed at the TVsnative resolution.

Poor scaling can result in artifacts, such as jagged edges and inconsistent detail. It must also benoted that results also depend on the quality of the incoming signal.

y Definition of the Term: UpscalingDefinition: Upscaling is a process that mathematically matches the pixel count of the output of a


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standard or non-hi-def signal (such as standard DVD) to the physical pixel count on an HDTV,which is typically 1280x720 (720p) or 1920x1080 (1080i or 1080p) .720p represents 1,280 pixels displayed across the screen horizontally and 720 pixels down thescreen vertically. This arrangement yields 720 horizontal lines on the screen, which are, in turn,displayed progressively, or each line displayed following another.1080i represents 1,920 pixels displayed across a screen horizontally and 1,080 pixels downascreen vertically. This arrangement yields 1,080 horizontal lines, which are, in turn, displayed in

two successive fields of 540 lines (interlaced scan).1080p represents 1,920 pixels displayed across a screen horizontally and 1,080 pixels down ascreen vertically. This arrangement yields 1,080 horizontal lines, which are, in turn, displayedprogressively.

Also Known As: Up Scaling, Video Upscaling

Motion Response TimeThe ability for an LCD TV to display fast moving objects has, in the past, been a weakness of LCD

technology. However, this has improved dramatically. This does not mean that all LCD TVs arecreated equal in this area.Check the specifications for Motion Response Time (ms = milliseconds). A good LCD TV now shouldhave a Response Time of either 8ms or 4ms, with 4ms being optimum, especially if you watch lots

of sports or action films. Be wary of LCD TVs that do not list their motion response time.Another factor that can add support to response time is Screen Refresh Rate.

y Video Frame Rate vs Screen Refresh RateShopping for a television these days is certainly not as easy as it once was. With terms being

tossed around like HDTV, ProgressiveScan, 1080p, Frame Rate, and

Screen Refresh Rate, theconsumer is getting drowned with tech terms that are difficult to sort through. Of these terms, two

of the most difficult to make sense of are Frame Rate and Refresh Rate.What Frames AreIn video (both analog and high definition), just as in film, images are displayed as Frames.However, there are differences in the way the frames are displayed on a television screen. Interms of traditional video content, in NTSC-based countries there are 30 separate frames displayedevery second (1 complete frame every 1/30th of a second), while in PAL-based countries, there

are 25 separate frames displayed every second (1 complete frame displayed every 25th of asecond). These frames are either displayed using the Interlaced Scan method or the ProgressiveScan method.However, since film is shot at 24 frames per second (1 complete frame displayed every 24th of a

second), in order to display film on a typical television screen, the original 24 frames must beconverted to 30 frames by a process known as 3:2 pulldown.What Refresh Rate Means

With the introduction of television display technologies, such LCD, Plasma, and DLP, and also Blu-ray Disc and HD-DVD, another factor has entered into play that affects how frames of videocontent are displayed on a screen: Refresh Rate. Refresh rate represents how many times theactual Television screen image is completely reconstructed every second. The idea is that the more

times the screen is "refreshed" every second, the smoother the image is in terms of motionrendering and flicker reduction.In other words, the image looks better the faster the screen can refresh itself. Refresh rates oftelevisions and other types of video displayed are measured in "hz" (Hertz). For example: ATelevision with a 60hz refresh rate represents complete reconstruction of the screen image 60times every second. As a result, this also means that each video frame (in a 30 frame per secondsignal) is repeated twice every 60th of a second. By looking at the math, one can easily figure outhow other frames rates related to other refresh rates.

Frame Rate vs Refresh RateWhat makes things confusing is the concept of how many separate and discreet frames aredisplayed every second, verses how many times the frame is repeated every 1/24th, 1/25, or

1/30th of a second to match the refresh rate of the Television display.TVs have their own screen refresh capabilities. A television's screen refresh rate is usually listed inthe user manual or on the manufaturer's product web page.The most common refresh rate for today's Televisions are 60hz for NTSC-based systems and 50hz

for PAL-based systems. However, with the introduction of some Blu-ray Disc and HD-DVD playersthat can actually output a 24 frame per second video signal, instead of the traditional 30 frame persecond video signal, new refresh rates are being implemented by some television display makersto accommodate these signals in the correct mathematical ratio.

If you have a TV with a 120hz refresh rate that is 1080p/24 compatible (1920 pixels across thescreen vs 1080 pixels down the screen, with a 24 frame per second rate). The TV ends updisplaying 24 separate frames every second, but repeats each frame according to the refresh rateof the TV. In the case of 120hz each frame would be displayed 5 times within each 24th of asecond.In other words, even with higher refresh rates, there are still only 24 separate frames displayed


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every second, but they may need to be displayed multiple times, depending on the refresh rate.To display 24 frames per second on a TV with a 120hz refresh rate, each frame is repeated 5 timesevery 24th of a second.To display 24 frames per second on a TV with a 72hz refresh rate, each frame is repeated 3 timesevery 24th of a second.To display 30 frames per second on a TV with a 60 hz refresh rate, each frame is repeated 2 timesevery 30th of a second.

To display 25 frames per second on a TV with a 50 hz refresh rate (PAL Countries), each frame isrepeated 2 times every 25th of a second.To display 25 frames per second on a TV with a 100 hz refresh rate (PAL Countries), each frame isrepeated 4 times every 25th of a second.

NOTE: The above explanation is with pure frame rates. If the TV also has to do a 24 frame persecond to 30 frame per second or vice versa frame rate conversion, then you also have to dealwith 3:2 or 2:3 Pulldown, which adds more math. 3:2 pulldown can also be performed by a DVD orBlu-ray Disc player, or other source device, before the signal reaches the TV. For more details,

check out an explanation posted by HH Gregg.How TVs Handle 1080p/24 If a TV is 1080p/60 or 1080p/30 - only compatible, it would not accept the 1080p/24 input.Currently, only Blu-ray Discs and HD-DVD discs are the main sources of 1080p/24 material.

However, most Blu-ray Disc and HD-DVD players convert the outgoing signal to either 1080p/60or 1080i/30 so that the information can be processed by a TV properly for screen display if it is notcompatible with 1080p/24.

NOTE:Although 1080p/60-only TVs cannot display 1080p/24 - 1080p/24 TVs can display1080p/60 via video processing.Final TakeThe whole thing boils down to the concept of separate frames vs repeated frames. In the case of

frame rate vs refresh rate calculations, repeated frames are not considered separate frames as theinformation in the repeated frames is identical. It is when you move to a frame with differentinformation that you count it as a new frame.With more sophisticated technologies being employed in today's HDTVs, it is important thatconsumers arm themselves with the knowledge of what is important and what isn't. With HDTV,the concept ofScreen Refresh Rate is indeed important, but don't get bogged down with thenumbers.The important thing to take into consideration is how the increase in Refresh Rate improves, or

doesn't improve, the perceived screen image quality for you, the consumer. Let your own eyes beyour guide as you comparison shop for your next television.

Contrast Ratio

Contrast ratio, or the degree of variation of the whitest and darkest parts of the image, is a very

important factor to note. If the LCD TV has a low contrast ratio, dark images will look muddy andgray, while light images will look washed out.Also, don't get seduced by Contrast Ratio marketing hype. When checking contrast ratio numbers,look for Native, Static, or ANSI contrast, not Dynamic or Full On/Full Off contrast. ANSI contrastrepresents the difference between black and white when both are on the screen at the same time.Dynamic or Full ON/OFF contrast only measures black by itself and white by itself.

y Definition of the Term: Contrast RatioDefinition: Contrast ratio is the difference between the brightest whites and the blackest blacksthat a television or video projector can display. High contrast ratios deliver whiter whites andblacker blacks and a greater degree of gray values in between. If the contrast ratio is low, even ifthe image is bright, your image will look washed out. Beware of outrageous contrast ratio numbersbased on "Dynamic" or "On/Off" numbers. Look for contrast ratio numbers that refer to "Native" or

"ANSI" numbers.

y The Contrast Ratio Game

A Popular Trend: Playing with Contrast Performance FiguresBig numbers sell better, and manufactures know this very well.

This number battle is everywhere, from the use of interpolated, instead of true opticalimage resolutions in digital image scanners and cameras, to the latest 240Hz and

480Hz refresh rates in LCDs and the 600Hz sub-field drive in plasma displays. It is as

if manufactures do their best to come with the biggest number to deliver the messagethey have the best product.However numbers on their own do not mean anything; unless you know what you arereally talking about, one may end up misinterpreting facts.The same applies to contrast ratio. By 2004, TV makers came up with an

unprecedented 4,000:1 contrast ratio. By 2007, figures for contrast ratio reached15,000:1 and in 2008 we saw the first 1,000,000:1 contrast rating for LED TVs andplasma HDTVs. Now we have multi-mega contrast ratios. There is really no limit to


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how much these numbers can continue to grow.

Yet this contrast ratio issue is more than just numbers. Apart from the fact that mostTV makers often fail to differentiate between static and dynamic contrast- some TV

manufactures are taking consumers for a ride by quoting ultra high ratings for

contrast ratio using unspecified test methodologies. Their purpose is to help sell theirproducts over that of the competition.

We are not saying that the latest mega-contrast ratings associate with some HDTVsare incorrect - most probably they are correct if measured in a totally dark roomenvironment. But...

What is actually being measured by these display manufactures?

Does this dark room setting represent the typical viewing environment,

andhow does ambient light affects the resultant contrast ratio of a

display device?

What is the implication on perceived contrast by the eye - is this as much

as manufacturers are trying to imply with their big numbers?

What is Contrast: Defining and Measuring Contrast RatioContrast is the ratio between the white and black parts in an image. A contrast rating of

300:1 means that the luminance or brightness level of the white areas in the image is300 times brighter than that of the blacks. The larger the contrast ratio, the greater the

difference between the brightest whites and the darkest blacks a display device can

produce.Contrast is an important image quality attribute that affects our ability to perceive bothimage brightness and image detail. Without a sufficient level of contrast, images appear

flat with the blacks and white taking a gray shade while finer image detail would be lost.Static or Dynamic?Static contrast refers to a display device native contrast ratio. It isthe more important of the two despite being smaller as it represents the 'true' contrast

i.e. the darkest blacks and the brightest whites that a display can simultaneously supportat any one time.

Instead, dynamic contrast refers to the maximum ratio between the deepest blacks adisplay can show and the brightest whites it can handle over its entire operational range

but not at the same time. A display device will never be able to handle these two

extremes simultaneously.Dynamic contrast uses a processor inside the display to analyze the average, overall

picture brightness and adjusts the backlight level on-the-fly. This helps render deeperblacks in predominantly dark scenes and brighter whites in mostly bright picture content.When done properly, dynamic contrast can give the impression of higher contrast ratios

and solid black levels; done poorly, it can crush black to the point of losing shadow

detail.Yet dynamic contrast may also alter the tone response characterizes, or gamma setting

of the display and the video signal on-the-fly to produce what most consider a moreattractive image. But altering these characteristics means that the presented image may

not necessarily be a true and faithful representation of the original video signal. Thismay not be an issue with video games and most TV content, but it is with material ofartistic nature.As expected, the dynamic contrast ratio results in much larger numbers and is often thecontrast ratio most quoted by TV makers.Measuring Contrast RatioThe two methods mostly used by the projection and video display industry to determinecontrast performance of a device are the Full On/Off, and the ANSI Contrast ratiomeasurement:

Full On/Off Contrast is the ratio of the light output of an all white image(full on) and the light output of an all black (full off) image. This is the most

favored measurement by manufactures as it yields a larger number for thecontrast ratio - 25% to 100% more - than ANSI Contrast measurements for

the same display device. Some manufactures of DLP-based displays would

even carry this contrast ratio measurement with the 'white segment' of thecolor wheel turned; this increases the measured figures for the white

luminance, hence inflating further the end result.


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ANSI Contrastis measured with a

pattern of 16 alternating black and white

rectangles - also referred to as the'checkerboard' test pattern. The average

light output from the white rectangles is

divided by the average light output of theblack rectangles to determine the ANSI

contrast ratio.Checker-box image courtesy of

ausmedia.com.au

ANSI Contrast represents a more fair way to test contrast ratio as the presence of blackand white at the same time is closer to the real world environment rather than the allblack or all white image used during the full ON/OFF contrast measurement. This renders

the average reading obtained from the ANSI Contrast more realistic.It is thus clear that when comparing the contrast ratings ofhome theater projectors and

video display devices, it is essential to ensure you are comparing the same type of

contrast. Full On/Off contrast will always be a larger number than ANSI contrast for thesame projector or monitor.

Unfortunately, there is nothing mandatory as to the methodology used by manufactures

to measure contrast performance. Even worse, manufacturers are not obliged to specifythe method used to arrive at the quoted figures.This renders a straightforward comparison of contrast performance figures between

different imaging devices - especially from different manufactures - almostmeaningless.

Don't be impressed withBIG Contrast Numbers!

Making theDisplay: Contrast Ratio Facts ...and numbersContrast is an important attribute in a display or video projector performance and helpsmake an image 'pop-up' as it affects our perception of color differences apart from image

brightness. A minimum level of contrast is necessary for the eye to perceive an image as

'bright'. Studies show that for a binary black and white image, a minimum contrast ratioof 2 is necessary for comfortable viewing, while a contrast ratio of between 5:1 and 7:1is necessary for the eye to distinguish color differences.

Yet, today's video projectors and flat-panel TVs come with more than just a minimumlevel of contrast. The latest home theater video projectors from Sanyo (PLV-Z3000) and

Panasonic (PT-AE3000U) have a rated contrast ratio of over 60,000:1. Even more

impressive are the latest plasma and LED TVs with their mega contrast ratings. PlasmaTVs such as Samsung PN50B650 and LG 50PS80 come with at least 2,000,000:1

contrast ratio, while Samsung UN46B7000 LED TV has a quoted 3,000,000:1 contrastratio!

Yet, the truth is that contrast cannot be taken on its own. A high contrast ratio can be

misleading at best if used incorrectly; and in the promotional media, it can even turn outto be a lie.

A higher contrast ratio implies a device has greater ability to display black as 'a deeper

black' instead of dark gray with respect to its brightest whites. A home theater projectorwith a contrast ratio rating of 8,000:1 is more capable of showing a dark subject than

one with an 800:1 contrast ratio. But the difference in performance between the twowould only become apparent if projection takes place in a completely dark room, one in

which is there no light other than that of the projected image.

Equally important is that the eye would not detect a 10 times improvement in contrastperformance between these two projectors. Rather, the perceived difference in image

performance between these two devices would be just marginaland detectable only ifthe room is in total darkness.Marginal because the eye contrast sensitivity is not linear. While a difference in a

contrast ratio of between 10:1 and 20:1 will be definitely distinguishable and adifference between 100:1 and 200:1 as clearly visible, the eye would see the differencebetween say 400:1 and 800:1 as a minor change. And anything above 1000:1 may not

be visible at all.And it is detectable only in the total absences of ambient light because as we will seefurther in this article, complete absence of stray light in a room is critical when it comes

to contrast performance. This is a rather rare situation in everyday life unless viewing


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takes place under a controlled environment, such as that of a dedicated home theater

with black painted walls.This absence of light in contrast performance is important as the brightness level of what

the eye perceives as black in comparison to the brightest parts of the image, can only be

as low as the light reflected by the darkest parts of the image. This applies irrespectiveof whether the image is being displayed on a projection screen or a direct-view display

such as that of an LCD or plasma TV.Any ambient light will be reflected by the projection screen surface, or the glass surface

and the internal display structure in the case of a direct-view display, thus turning black

into what may appear as some shade of gray. This lowers image contrast considerably.Direct-view systems however have the advantage that their contrast performance is

significantly less affected by the presences of light in the room. This is mainly thanks to

the optical coatings on the display screen surface that help block external light fromentering the display panel, and the use of a black surface structure inside the display

between adjacent pixels to block more of the ambient light from entering the display.

Presence of Ambient Light and Contrast Ratio

With this muchlight in the room,

there is nodifference

between 900:1and 10,000:1

Contrast Ratio!

Presence of light: To better understand the impact of the presence of light in a room

on the contrast ratio performance, consider the light emitted by just one candle in a

room one meter away from a display surface whose black level stands at 0.1 cd/m2 intotal darkness. This is sufficient to render the image from say a 10,000:1 rated

contrast ratio video projector the same as one projected by a 900:1 CR rated projectorwhen the latter is displayed in a totally dark room!

Increase the light in the room to approximately 30 LUX; this corresponds to the light

emitted by a small incandescent lamp. Contrast figures above 100:1 would now turnout to be simply academic even in the case of video projectors with say a relatively

high 2500 ANSI Lumens brightness rating. Why?

To maintain a 'low' 200:1 contrast ratio under 30 LUX of ambient light, your projectorhave to generate more than 6000 LUX for the brightest areas. But to maintain this level

of brightness over say a 100-inch diagonal 16:9 unity gain screen (30 square ft), youneed a projector with at least 16,000 ANSI-Lumens output. Your 2500 ANSI Lumensprojector will never maintain a 200:1 contrast even in a dimly lit room, least image itsquoted 10,000:1 contrast ratio under the presence of higher levels of ambient light. (Formore information on projector screens and video projector output, please refer to our

article: Understanding projector screens.)Let's continue playing with numbers! To better understand the whole issue of thepresence of ambient light and its effects on contrast performance, consider a contrast

rating of say 2,500:1 and a maximum luminance level of 250 cd/m2 for the brightestpart of the image. Then the darkest part of the image will have a luminance of just 0.1cd/m2 in the complete absence of ambient light.

Let's introduce the presence of a dim light source in the room and assume that just 5

cd/m2 of this light is being reflected by the screen surface.Contrast ratio would than change as follows:

= While Luminance/Black Luminance

= (250 + 5)/(0.1 + 5) or 255/5.1 = 50:1This means that our contrast ratio has now changed from the original 2,500:1 to just

50:1!


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And it only takes a very dim light source for a display to reflect as much as 5 cd/m 2 of

light. A shinny screen surfaces such as that of a CRT may easily reflect as much as 80%of the light falling on the screen.

It is thus clear that unless you watch your moves in a completely dark environment, it

would be useless to stress too much and pay more for a device with a too high contrastratio rating!

Important Factors worth considering:Contrast and Brightness:As already stated, contrast does not stand on its own! Ahigher image brightness level would yield a better perceived contrast ratio for a fixedlevel of ambient light. This means that a projector with a lower contrast ratio but withhigher rated lumens output may under certain light conditions, perform better than one

with a higher contrast ratio but lower brightness level.Cinema: It is interesting how present-day digital cinema projection equipment performswith respect to contrast ratio. Typical contrast ratio is 1000:1; however, this variesaccording to make and model. For example, one of the world's most popular digital

cinema projectors, the Christie CP2000 2K 3-chip DMD DLP Cinema, despite its 35trillion colors, has a contrast ratio rating of just 500:1 ANSI, 2000:1 full field.

Note: The reference here to the performance of digital cinema projectors applies to

contrast ratio. When it comes to image resolution, traditional 35mm and in particular70mm movie film systems support far greater image detail than that supported by

professional digital cinema equipment today. Grayscale:While contrast is an important attribute, contrast alone does not provide

useful picture information - only the various levels of gray does. It is the grayscaleperformance of an imaging device - its ability to represent various levels of luminancelevels - that is the single most important attribute to consider. Larger number of grayscales or shades of gradation implies a device greater ability to display subtle detail in

dark or bright scenes, while creating a wide color palette. Without shades of gray,contrast alone is of no use in delivering image information.

Your eyes are the limiting factor!

The Human Eye: an issue on its own!The eye is not an absolute sensor - what the eye sees are brightness differences. Unlikeelectronic sensors in digital imaging systems - which are all absolute in their response,

the eye has a dynamic response to contrast - also referred to as dynamic range. This

alters the whole equation in that what is really important is not some unrealistically highabsolute ratio rating, but rather, how the end image is perceived by the eye. Why?

The eye is an extremely complex sensor with far greater response range than any film ordigital imaging device. It is able to function both in bright sunlight as well as in very faintlight during the night - that's a range of over 10 million to one! In photographic terms,

that's about 23 1/2 stops.At the same time, it is not possible for the eye to see the faint light from a star in the

sky during the day. From a photographic perspective, this is like saying that a camera

can operate over an extended range, but then the full operating range is achieved byadjusting the film ISO speed, the camera aperture setting, and even the exposure time.

It is the same with the eye; at any given instant, the eye can possibly see over a range

of 400 to 800:1 in contrast detection. Some may even see up to 1,000:1 and possibly alittle beyond but the eye would not detect any difference above approximately 1,000:1.

For anything above that, the whites would be already too bright and the blacks would be

too dark for the eye to distinguish any further detail.The wider dynamic range of the eye is possible as once the eye moves (saccades), it re-

adjusts its exposure both chemically and by adjusting the iris. Over time, it is possiblefor the eye to resolve a contrast ratio range (sort of the dynamic contrast range in

HDTVs) of between 1,000,000 and 10,000,000:1.But the eyes' ability to detect contrast depends on the scene brightness, with thecontrast sensitivity of the eye decreasing to about 8% of its maximum at low light

levels; the eye sensitivity also decreases with lower contrast subjects.To complicate matters, the eye Contrast Sensitivity Function (CSF) is not linear - in asmuch as it decreases with a decrease in brightness, there is a brightness level abovewhich the eye contrast sensitivity falls once again. It is estimated that the sensitivity of

the eye is some 600 times less in bright sunlight.


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At low light levels, the eye is able to integrate image information over a period of some

15 seconds to be able to see dimly lit subjects (it is like when you increase the cameraexposure time to record subject information during low light level conditions ).

However, moving from one brightness range to another would take time for the eye to

adapt. A 'dark-adapted' eye would be able to see a faint star in the sky, but this darkadoption process by the eye takes 30 minutes or so to complete - provided you haven't

been exposed to bright sunlight during the day, otherwise, it may take even up to onehour for full adaptation to take place. Looking at a bright subject by a dark adapted eye

would simply kill your night vision

This implies: The first 30 minutes or so during a movie are not the best in terms of

contrast sensitivity. What's more, looking at a bright movie scene would not help when

the next dark scene comes around!

And as if this is not enough, there are other factors as well that affect our contrast

perception. For example, the eye would perceive a higher contrast when looking at staticimages than it would if it were to look at moving pictures even if these were to have

similar contrast ratio to that of the static scene.There is also the issue of the eye contrast sensitivity with spatial frequency.

Technically speaking, spatial frequency is the number of cycles subtended at the eye per

degree of vision.

It can be thought of gaps between adjacent imageparts that vary in contrast. There is a point abovewhich increasing the spatial frequency i.e.decreasing the gap between adjacent image parts,will reduce the eyes sensitivity to contrast even

though the contrast level of the image remainsthe same.

And what about the loss of contrast sensitivity with age? The amount of light reaching

the eye photoreceptors diminishes as we grow older; this in turn affects the eyes'

response to brightness and contrast perception.

So what's the whole discussionhere?Do not get carried away with big contrast numbers. The eye dynamic response is thelimiting factor; at any one point in time, you would not be able to perceive a contrast

ratio of more than at most 1,000:1 - irrespective of display technology.Equally important is that the presence of even a minimal amount of ambient light would

make a home theater projector or a direct-view display device with a high contrast ratio

rating behaves the same as one with a much lower rating. Direct-view systems are lessaffected in this respect though their blacks would still suffer under a bright light

environment.Opt for a high contrast projector or display device only as long as you can view theimage in a light controlled room. Despite what might seem to be a huge difference in

absolute terms between say a 1,000:1 and a 1,000,000:1 contrast ratio, you will have to

view the image in a completely dark room to perceive the resultant minimal differencein picture performance. Paying extra just to enjoy a higher contrast ratio is just waste of

money.Conclusion: Numbers are there to impress and help the marketing people sell the

product. But quoted peak contrast ratings do not really give you any information on thevideo projector or display device ability to render images with lifelike gray scales andcolors. Rather, the only information that contrast ratio can deliver is how much brighter

the 'whites' can be than the 'blacks'!BrightnessWithout sufficient brightness your image will look muddy and soft, even in a dark room. Viewingdistance, screen size, and ambient room light will affect the need for more brightness capability.A brightness rating listed as 550 cd/m2 or higher is good, however, don't get bogged down withthe technical number listed, just make sure the screen is bright enough for your needs upon yourown visual inspection.


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Viewing AngleMake sure you can view the image on the LCD TV from the sides as well as the from the primeviewing area. LCD TVs typically have a good side-to-side viewing angle, with many going as wide

as 160 Degrees, or about 80 degrees from the center viewing spot.If you find that the image begins to fade or becomes unviewable within 45 degrees from eitherside of the center viewing spot, then it may not be a good choice where you have a large group ofviewers sitting in different parts of the room.

Tuner and Connection ConsiderationsAlmost all LCD-TVs now have both built-in NTSC and ATSC tuners. An ATSC tuner is required toreceive over-the-air TV broadcast signals after June 12, 2009. Also, some LCD TVs have what is

referred to as a QAM tuner. A QAM tuner is what is required to receive unscrambled HD-Cableprograming without a cable box.In addition, the LCD TV you purchase should have at least one HDMI input for the connection ofHD sources, such as HD-cable or Satellite Boxes, Upscaling DVD or Blu-ray Disc player.

Question: Can I Also use an LCD TV as a Computer Monitor?Answer: The presence and growth of LCD television certainly has its roots in the development andsuccess of LCD computer monitors, and, thus share a great deal of characteristics with them. MostLCD televisions have VGA (PC Monitor) input connections that allow them to be used as a

computer monitor.However, if your main purpose is to use an LCD display as computer monitor, the additional cost ofthe features of an LCD television, such as a built-in analog or HDTV tuner, analog AV and HDMIinputs, and other features needed for television-like performance, may be extra things you maynot need.In addition, if you are a gamer or have your PC integrated into your home theater system, andwant the largest possible monitor to play on and show off to your friends, a 32-inch, or larger, LCD

television can be a very impressive computer monitor.If you are planning to use your LCD TV as both a television and computer monitor, make sure theunit your are considering does have VGA or other connection options designed for PC use.

before you buy an lcd

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