LCD Image Persistence

LCD Image Persistence

Can Burn-In Happen to LCD Monitors?

출처 : http://compreviews.about.com/od/monitors/a/LCDBurnIn.htm

By Mark Kyrnin, About.com

Introduction

One of the problems with CRT monitors over time was a condition called burn-in. This resulted in an imprint of a image onto the display that was permanent. It was caused from the continuous display of a particular image on the screen for extended periods of time. This would cause a breakdown in the phosphors on the CRT and would result in the image being burned into the screen, hence the term burn-in.

LCD monitors use a very different method for producing the image on the screen and are supposed to be immune to this burn in effect. Rather than phosphors being used to generate the light and color, an LCD has a white light behind the screen and then uses polarizers and crystals to filter the light to specific colors. While LCDs are not susceptible to the burn-in the same way CRT monitors are, they do suffer from what the manufacturers like to call image persistence.

What is Image Persistence?

Like the burn-in on CRTs, image persistence on LCD monitors is caused by the continuous display of static graphics on the screen for extended periods of time. What this does is cause the LCD crystals to have a memory for their location in order to generate the colors of that graphic. When a different color is then displayed in that location, the color will be off from what it should be and instead have a faint image of what was previously displayed.

This problem is most common for elements of the display that do not change. So items that are likely to generate a persistent image are the task bar, desktop icons and even background images. All of these tend to be static in their location and will be displayed on the screen for extended period of time. Once other graphics are loaded over these locations, it may be possible to see a faint outline or image of the previous graphic.

Is it permanent?

In most cases, no. The crystals do have a natural state and can shift depending upon the amount of current used to generate the desired color. As long as these colors do shift periodically, the crystals at that pixel should fluctuate enough such that the image will not be permanently imprinted into the crystals. Having said that, it is possible that the crystals could get a permanent memory if the screen image does not change at all and the screen is left on all the time. It is very unlikely for a consumer to have this happen as it is more likely to happen in a fixed display such as those seen as display boards for businesses that do not change.

Can it be prevented/corrected?

Yes, image persistence on LCD screens can be corrected in most cases and is easily prevented. Prevention of image persistence can be done through some of the following methods:

1. Set the screen to turn off after a few minutes of screen idle time under the Power functions in Windows. Turning the monitor display off will prevent an image from being displayed on the screen for extended periods of time. Of course, this could be annoying to some people as the screen may go off more than they wish.
2. Use a screen saver that either rotates, has moving graphic images or is blank. This also prevents an image for being displayed in screen for too long.
3. Rotate any background images on the desktop. Background images are one of the most common causes for image persistence. By switching backgrounds every day or few days, it should reduce the change of persistence.
4. Turn off the monitor when the system is not in use. This will prevent any problems where the screen saver or power function fails to turn off the screen and result in an image sitting on the screen for long times.

Using these items can help prevent the image persistence problem from cropping up on a monitor. But what if the monitor is already displaying image persistence problems? Here are a few steps that can be used to try and correct it:

1. Turn off the monitor for extended periods of time. It can be as little as several hours or it could be as long as several days.
2. Use a screen saver with a rotating image and run it for extended periods of time. The rotating color palette should help remove the persistent image but it could take a long time.
3. Run the screen with a single solid color or bright white for an extended period of time. This will cause all of the crystals to be reset at a single color setting and should erase and previous image persistence.

Conclusions

While LCDs don't have the same burn-in problem that affected CRTs, the image persistence problem could come about. Hopefully this article has addressed what the issue is, what causes it, how to prevent it and how to correct it. With all the preventative steps in place, a user should never really have to encounter this problem.




또 다른글
출처 : http://www.techlore.com/article/10099/Do-LCD-TVs-Burn-In-/

Do LCD TVs Burn In?

What Is Burn In?

Burn in is one of the most commonly misunderstood concepts regarding television displays. Burn in is a phenomenon associated to television products, in which a static image left on the screen, over time, can permanently wear itself into the display. This issue is generally associated to phosphor based television displays like tubes, CRT rear projection, and plasma displays.

A common question asked is if LCD televisions are susceptible to burn in. The most common answer given to this question is no, LCDs are immune to burn in. However, this answer is somewhat of a half-truth.

The Truth About LCD and Burn In

It is a fact that LCD displays are immune to phosphor wear, simply because LCD televisions do not use phosphor to create a television image. Otherwise, it would be like saying an electric car can run out of gas.

However, LCD displays have certain characteristics that do not make them completely immune to static images. On LCD displays it's kindly referred to as "video memory." LCD panels use a complicated process of organizing liquid crystal molecules into a twisted or untwisted state, which allows polarized light to pass through the liquid crystal substrate. Over time, it is possible the liquid crystals can "get used to" the state of twist they are in, causing a static image, similar to phosphor burn-in, appear on the screen.

Some say that simply turning off the display for 24-48 hours eliminates the effect, while others have claimed the effect is permanent in extreme cases. Nonetheless, home users of LCD televisions have little to fear.

Why Video Memory Is Little Concern To LCD TVs

The nature of LCD products makes them extremely resilient to building up a video memory. In fact, you're far more likely to see this issue on LCD computer monitors. If, for example, the Windows or Macintosh desktop was left uninterrupted on a LCD display, with no screen saver for an extremely long period of time, impage persistence could become an issue and (possibly) be permanent.

LCD televisions, on the other hand, typically get enough image movement or power cycles that the buildup of video memory is highly unlikely. Leaving static images on an LCD display for a relatively short period of time will have no damaging effect to the display.

In other words, you'll only get video memory buildup on an LCD television if you try to do it on purpose or step well outside the norm when viewing static images.

What's outside the norm? Viewing a large amount of 4:3 programming on a widescreen display with static bars on the side can, as community members have pointed out in the comments area below, increase your risk of video memory or image persistence... even on LCD displays. While I still don't find it 'likely' that this commonly occurs, it's always prudent to limit viewing of static images whenever possible, so do yourself a favor and take advantage of the various formatting modes your television provides.

Better To Be Safe Than Sorry

Considering a large majority of television and movie content is optimized for widescreen displays these days, there's little need for the typical television watcher to concern themselves with video memory. It's just not likely under normal viewing conditions, but it never hurts to be safe than sorry. Follow these tips to ensure a video-memory-free experience with your LCD TV:

• Limit your viewing of 4:3 material on widescreen TV with static bars. Use the formatting modes on your TV to reformat 4:3 material to fit the 16:9 screen. Also, don't watch 1000 2.35:1 ratio DVD or Blu-Ray movies in a row. 
• Be careful of channels that maintain a static, never moving, logo somewhere on the screen.
• Be careful when playing video games that contain a static graphics, like a life meter or HUD. Make sure you vary your gaming or watch other things between gaming sessions.
• Be careful of channels with stock tickers and other non-moving images