HDTV Buying Guide – Myths and Assumptions Demystified

Article by Rama:

When choosing an HDTV, you need not consider resolution, plasma burn-in and LCD motion blur as factors affecting your buying decision. Even picture quality is not something to worry too much about. The factors that you should consider are your viewing conditions and the features you want in your TV.

If you’re a first time HDTV buyer, make sure you read through the summary and the gists first. Consider this a starting point to your HDTV research. You won’t find information about specific models here but you’ll get a broad perspective on what to look for when buying a HDTV.

WHAT’S NOT IMPORTANT

1. HDTV Resolution

Gist: Irrespective of TV size, 1080p resolution will give negligible improvement over 720p. Even cinema screenings have a resolution of ‘only’ 750p. The only reason to choose 1080p over 720p is when the 1080p TV in question has better specs (contrast ratio etc.) than the 720p TV in question.

Before analyzing why resolution isn’t important, here’s an interesting fact – the resolution of movies we see in movie theatres is around 750p (ie. 750 horizontal lines of resolution). It’s surprising but it’s true. Films are usually reprinted at 2K resolution (2048×1080) because that’s more cost effective than reprinting at higher resolutions and because higher resolutions than 2K don’t give noticeable improvement even on cinema screens. Because projector lens optics are not perfect, the 2K resolution when magnified on screen further degrades and comes down to around 750p. Here’s a paper detailing how this figure was obtained – http://www.cst.fr/IMG/pdf/35mm_resolution_english.pdf

Now, you might think Full HD TVs will give you a picture that’s even better than cinema theatres. That’s not true. Full HD TVs claim a resolution of 1920×1080 but this is true only for still images. The video resolution or moving picture resolution for many LCDs and plasmas come down to 800p or sometimes even down to 300p. This is because of the inherent technological shortcomings found in LCDs and plasmas. Also note that though some TV specs quote a moving picture resolution of 1080 lines, the actual measured resolution will be much less. (Refer CNET HDTV reviews to cross-check a TV’s moving picture resolution as they usually provide moving picture resolution measurements in their reviews.)

Comparing HD ready and full HD TVs, people usually find that full HD TVs are sharper for bluray material. This observation is not necessarily because 1080p has more pixels and therefore more detail; the true reason for improved sharpness is the lack of scaling in full HD TVs. Full HD TVs and bluray material have the same resolution (1920×1080). So the pixel mapping is one-to-one and scaling is not required. HD ready TVs have either 1024×768 (plasma) or 1336×768(LCD) resolution, so bluray material is shrunk to fit the screen’s native resolution. This shrinkage causes some blurring. Even if one sits right in front of the TV, he’ll have a hard time making out what extra visual detail 1080p gives over 720p. Here’s a very good image comparing video resolutions – http://blog.isnoop.net/wp-content/up…view_large.png In reality, the difference will be even less apparent than what this pic shows.

For games, resolution differences might be apparent but then all mainstream console games have a native resolution of 720p or less (so these games will look razor-sharp even on HD ready TVs). That said, bigger resolutions do make a difference when viewing static content like test charts and when browsing webpages. Unless you want to use your TV to browse the internet and have multiple webpages tiled side by side in full size, you absolutely need not worry about HDTV resolution irrespective of the TV’s size.

2. Plasma Burn-in

Gist: Burn-in is not a myth but it certainly is an easily preventable problem. A little precaution during the ‘run-in’ period is all that is needed to avoid burn-in forever.Burn-in is no myth. You can leave permanent burn-in marks at will on any plasma TV (even on a top end Pioneer Kuro). But to create burn-in even in a budget plasma, you’ll need to keep brightness and contrast at scorching levels and before you damage your TV you’ll certainly damage your eyesight.

I can tell you this from personal experience with my budget plasma. The budget plasma I used to own was found to be a demo piece and it came home with brightness/contrast set at a scorching 80/90 and had burn-in marks. But after that I had used it for 2.5 months (before it was returned for full refund; that’s a different story.), gaming and watching letterboxed movies (no TV channels tho) with brightness/contrast set at a fairly high 50,85 and I’ve never managed to create additional burn-in. But the original burn-in marks remained to be seen on the screen till the last day the set was at my home.

Generally, people mistake temporary image retention for burn-in. Image retention and burn-in are used as umbrella terms for a number of different issues –

1 – Phosphorescence – There is a long afterglow component of phosphors that can be seen even when the display is off. It is very faint however and eventually dissipates.

2 – Residual charge – Plasma displays use dielectric charges to control the on or off states of the pixel. If there is a slight residual charge left when the pixel is turned off the next time it turns on the pixel will be slightly brighter than normal. This will show up as a ghost image on a dark screen. You can tell it is residual charge because the ghost image is slightly brighter than the dark background. This ghost image is transient and easily removed by either a full white screen or watching full screen material for a few hours.

3 – MgO Sputtering – High energy discharge in Plasma displays causes Magnesium Oxide to sputter and deposit onto the phosphor and adjacent pixels. The result is a long lasting ghost image that can take many days to remove. It can be seen as a slightly darker image on a full white screen. Ironically, a full white screen for many hours is the best course of action to resolve this issue as it normalizes the deposition of MgO to all pixels (evens it out).

4 – Phosphor aging – Permanent aging of the phosphor material that causes a slightly darker ghost image that is irreversible.

Only phosphor aging is considered burn-in and it can be easily prevented by taking a simple precaution during the initial ‘run-in’ period of 100-150 hours – just keep contrast low. After the ‘run-in’ period, burning-in a plasma is impossible as long as brightness and contrast are not kept at eye-scorching levels or a still image is not left on the TV for hundreds of hours together. In fact, you’d be hard pressed to find even in online forums cases where people have actually reported burn-in. But remember, if you’re planning to use your TV as a computer monitor, then plasma is most certainly NOT the way to go because still areas like Windows ‘start bar’ and ‘title bar’ are left on the same place almost indefinitely and will probably create burn-in after a few months. But for normal TV usage, there should be no worries about burn-in when using plasmas – with budget plasmas you need to keep contrast low during the first 100-150 hours and for expensive plasmas you need not worry about burn-in at all because these sets are highly resistant to even temporary image retention, leave alone burn-in. Lastly, keep in mind that burn-in can occur even in LCDs because of permanently stuck pixels.

3. LCD/LED Motion Blur

Gist: LCD motion blur simply can’t be noticed in movies. Only when playing games or watching sports, motion blur can be noticed but even that can be eliminated.

Here’s another startling fact – the motion blur noticed in LCDs is not caused due to some drawback in LCD technology; it’s caused due to a weakness of the human eye – in the human eye bright images will persist for a fraction of a second. The blur noticed in LCD TVs is technically called sample-and-hold blur (or S&H blur). Unlike CRTs, LCDs do not light up pixels one at a time. Each frame of the video is displayed as a whole for a small period of time i.e. each frame is sampled and held on screen for a fraction of time and hence the name, sample and hold. Because of this method, each frame is seen by the eye fully for a long time and the eye takes some time to ‘un-see’ the old frame and see the new one. Thus, the persistent part of the old frame will be perceived as a blur. This doesn’t happen in CRTs because each pixel remains lit for a very small fraction of time and will be off before the eye tries to stamp the pixel’s image on itself. This doesn’t happen in plasmas too because, in plasmas, the pixels will be strobed (flickered on and off) a number of times for each frame. 600Hz subfield drive means that each 100Hz frame (or field) is strobed 6 times. This, in turn, reduces motion blur.

LCDs try to combat this problem by simulating what plasmas do. Pixel strobing is simulated by inserting a black frame in between every frame. If an LCD TV is strobed at 600Hz it will handle motion just as beautifully as a plasma. But then, LCDs have a problem where pixels will take some time to change colour (this is called response time). So, 600Hz strobing isn’t practically possible on today’s LCDs. However, some LCDs with advanced motion processing capabilities get creative and will insert an intermediate morphed frame between frames. This kind of motion processing usually gives a documentary look to movies and should not be turned on when watching movies. But, for movies, you need not turn on any kind of motion processing even on slow LCDs.

It’s impossible to notice motion blur in movies even on the slowest of LCDs. Why? Because of the nature of film capture, movies themselves will have more motion blur than what an LCD can introduce. Films, for logical reasons, are captured at a slow rate of 24 frames per second. The human eye can detect up to 72 fps when stationary and up to 300 fps when following moving objects on screen. So, 24 fps is, by its nature, quite blurry. This blurry motion is considered an inherent characteristic of movies and it is what makes movies look different from documentaries and TV programs.

That said, when playing movies, almost every HDTV owner will notice shaky motion on fast pan scenes. This artifact is called judder and it is not the same as motion blur. (Telecine)Judder is caused because of framerate difference between film material and PAL/NTSC standard refresh rate. In movies, frames change at 24Hz (or 24 frames per second) and TVs refresh natively at multiples of 50Hz (PAL) or 60Hz (NTSC). Most of the TVs sold in India have a native refresh rate of 100Hz. To convert 24Hz to 50Hz (or 100Hz), an approximation process called 2:3 pulldown is used. This process works really well for most scenes but rears its ugly head during fast pan scenes, where you’ll notice shaky motion. Only the most expensive TVs will be able to downplay judder. Specifically, TVs that have support for 96Hz playback or better will be able to play movies just as they were intended to be played. (TVs refreshing at 24Hz or 48Hz will show noticeable flicker.) But even on these expensive TVs you’ll notice some judder. Why? It’s because, just like motion blur, judder is also an inherent quality of cinema, owing to the low framerate of 24 fps. This is why handheld camera shots look very shaky and disorienting in movies but we don’t feel the same shakiness when we really walk or even play any recent FPS game. 24fps is the culprit but people have come to love it for its utility and aesthetics. So, the bottom line is that when watching movies, you need not worry a bit about motion blur even on the slowest of LCDs. But, sometimes motion blur will be noticeable when watching sports, especially when tracking moving objects like a tennis ball or a football or when playing games. When motion processing is turned on, these effects will be greatly reduced. So it’s a good idea to turn on motion processing when watching sports. Even if an LCD TV doesn’t have extra motion processing, motion blur won’t be a problem for the majority of the population. Only those with sensitive eyes will easily notice motion blur and these people will also notice phosphor trails and flickering on plasmas. So things get pretty even in the end.

4. Picture quality and the hundreds of parameters that try to define it

Gist: Under ideal conditions, no matter what HDTV you buy, it will give you very satisfactory picture quality for its price.

There’s a huge list of subjective and objective parameters that people use to define picture quality – black levels, color accuracy, color depth, contrast ratio, true contrast ratio, on-off contrast, checkboard contrast, image pop, natural look, 3d-ish picture and the list goes on and on to the depths of a videophile’s heart. Equally exhaustive is the list of picture defects – phosphor trails, edge halos, PWM noise, screen non-uniformity, dithering, slow response time, ABL, stuck pixels and this list goes on to the depths of a cynic’s heart.

It’s fun to understand what these terms mean but it’s very hard to correctly, objectively evaluate a TV’s picture quality without comparing the TV to a reference monitor. To most of us, showrooms are the only place where we can compare TVs but showrooms don’t have a reference monitor to benchmark picture quality nor do we take the pain to properly calibrate a display piece before judging it nor are showroom conditions similar to home conditions. It’s a good idea not to worry too much about picture quality parameters because finally, after understanding all these parameters our realization will be that these parameters don’t really make much practical sense. The funny truth about picture quality is, reference picture quality will be considered by most people to be very dull and boring. If you don’t believe this, just look around and see how dull and washed out real life looks compared to what you see on your TV!

The only thing to understand about picture quality is, no matter what HDTV you buy, be it the most expensive Pioneer Kuro plasma or a cheap 720p 26” LCD, it will give you very satisfactory picture quality for its price, under ideal conditions. Unless one knows what reference quality is and plans to use the TV exclusively for original blurays, one need not bother much about picture quality. The extravagant customer who spends in lakhs for a TV will enjoy thinking how his super-awesome TV beats the living crap out of any budget TV’s performance. The value-conscious customer will enjoy thinking how awesome a deal he got by not paying for useless features.

WHAT IS IMPORTANT

The most important thing to consider when choosing a TV is how badly the TV’s performance will degrade in non-ideal conditions and how probable it is to have such non-ideal conditions in your home. The most impactful factors that create non-ideal conditions are ambient light and viewing angle.

1. Ambient Light

The picture quality of plasmas degrades as ambient light increases. Specifically, black levels fall when ambient light increases because plasma displays (and some LCD TVs too) have reflective glass fronts. This is true for every plasma, even the might Kuro. But the degree of black level degradation will be high for budget plasmas and very little for ultra-expensive ones because the expensive ones will have better anti-reflective coating on the screen. When black levels degrade, they degrade contrast, color range and thus picture quality consequentially. In fact, in bright rooms with direct light sources, less expensive LCDs will overtake higher priced plasmas in picture quality. So, a plasma should not be considered if you have a bright room and don’t wish to control the light and make the room dimmer. The main reason why LCDs outsell plasmas is that most customers watch TV only in bright conditions.

2. Viewing Angle

The picture quality of LCDs degrades as viewing angle increases. Contrast and colours start taking a hit when viewing angle is increased. Expensive LED backlit LCDs with IPS panels may advertise 179 degree viewing angles but if you read reviews you’ll note that even the most expensive LED backlit LCDs with IPS panels are known to noticeably degrade in picture quality when viewing from even one seat away from dead centre. In the case of budget LCD’s, the degradation in picture quality will be even more pronounced. If you like to watch TV from up close (say, 5-7 feet for a 40-42 inch TV) and more than three people will be watching TV together most of the time, then LCDs will not be the right choice.

3. Features vs Price

Every TV offers good value for its price but you have to be sure if what it offers is what you want. Typical features to look for are on board sound quality (if you don’t plan to use external speakers), USB playback (if you don’t plan to use a DVD player), reference picture quality (if you’re a budding videophile who is willing to spend a lot on a TV), TV’s external design (if you’re décor conscious). Do understand that LED edge-lit LCDs don’t offer dramatic improvements in picture quality compared to normal LCDs but they look attractive with slim design and that is what commands the premium in price. Same is the case with many ‘stylish’ TVs. If you’re a budding videophile, you have to understand the law of diminishing returns – as the prices increase, the betterment in picture quality becomes smaller. Finally, a general buying tip – avoid big brand stores if you want good deals. By buying at a small store you don’t lose out on anything, as after sales service is taken care of by the manufacturer and not the dealer but you can be sure that you get the best price.

WHAT MAY BE IMPORTANT

Screen size: If you watch TV from far away (say >10 feet) then you will be inclined to get a bigger TV. (The THX recommended screen size for 10 feet distance is 90 inches!) In that case, you might consider plasmas because plasmas are usually cheaper for larger sizes. Remember, it’s a good idea to have two seating points – one for SD and one for HD because it’s simply impossible to get both SD and HD to look good from the same distance without compromising on one. Also, it’s a no-brainer that LCD is the only choice for smaller sizes because plasmas don’t come in smaller sizes. Know your recommended viewing distance/screen size here – Viewing Distance Calculator

Power Consumption: LCDs win hands down when it comes to power consumption. But do consider that even when comparing an efficient LCD to a power guzzling plasma by watching TV 10 hours a day, your yearly savings will be about Rs.2000. In practice your savings might be even less. So, plot your break-even graph before considering power consumption a criterion affecting your HDTV purchase. Compare HDTV power consumptions here – The chart: HDTV power consumption compared – CNET Reviews

SD processing: See how well or (how poorly) the TV processes SD content if you plan to watch lots of SD broadcasts and don’t wish to connect an external upscaler.