3M Touch Systems Image Sticking

3M Touch Systems Technical Note

Product: LCD Monitors – Image Sticking

LCD Monitors – Image Sticking

What is Image Sticking?

When utilizing TFT LCD panels in applications where a fixed or semi-fixed image remains displayed on the screen for extended periods of time, users may experience a phe nomenon referred to by the LCD industry as Image Sticking. Image Sticking - sometimes also called “image retention” or “ghosting”- is a phenomenon where a faint outline of a previously displayed image remains visible on the screen when the image is changed. It can occur at variable levels of intensity depending on the specific image makeup, as well as the amount of time the core image elements are allowed to remain unchanged on the screen. In POS applications, for example, a button menu which remains fixed, or in which the “frame” elements (core image) remain fixed and the buttons may change, may be susceptible to image sticking. It is important to note that if the screen is used exclusively for this application, the user may never notice this phenomenon since the screen never displays other content. `It is only when an image other than the “retained” image is shown on the screen that this issue becomes evident. Image sticking is different that the “burn-in” effect commonly associated with phosphor based devices.

What Causes Image Sticking?

Image sticking is an intrinsic behavior of TFT LCD displays due to the susceptibility to polarization of the interior materials (liquid crystals) when used under static, charged conditions (continuously displaying the same image). The individual liquid crystals in an LCD panel have unique el ect r ical properties. Displaying a fixed pattern - such as the POS menu described above – over prolonged periods can cause a parasitic charge build-up (polarization) within the liquid crystals which affects the crystals’ optical properties and ultimately prevents the liquid crystal from returning to its normal, relaxed state when the pattern is finally changed. This effect takes place at a cellular level within the LCD, and the effect can cause charged cry stal alignment at the bottom or top of a crystal cell in the “z” axis, or even crystal migration to the edges of a cell, again based on their polarity. These conditions can cause image sticking over an entire area, or at boundaries of distinct color change respectively. In either case, when the liquid crystals in the pixels and sub-pixe ls utili zed to

display the static image are polarized such that they can not return fully to their “relaxed” state upon deactivation, the result is a faint, visible, retained image on the panel upon presentation of a new, different image. The actual rate of image retention depends on variation factors such as the

specific image, how long it is displayed unchanged, the temperature within the panel and even the specific panel brand due to manufacturing differe nces amongst pane l manu f a cturers.

How Do I Avoid Image Sticking In My Display?

There are a number of things that can be done to minimize this phenomenon.

For Monitor Operators

- Try not to operate the LCD with a “fixed” image on the scree n f or more than 2 hours.

- If you are operating the monitor in an elevated temperature environment and with a

displayed image which is contrary to the recommendations in “For Software Developers” below, image stick can occur in as little as 30 minutes. Adjust your screen saver settings accordingly.

3M Touch Systems Technical Note

Product: LCD Monitors – Image Sticking

- Power down the unit during prolonged periods of inactivity such as the hours a store is

closed or a shift during which the piece of equipment isn’t used.

- Use a screensaver wit h a black or medium gr ay background that i s automatically set to

come on if the device is inactive for more than 5-10 minutes.

- Avoid placing the monitor in poorly ventilated areas or in areas that will create excess

heat around the monitor.

For Software Developers

- In defining the icons, buttons, or windows in the screen, try to utilize block patterns

instead of distinct lines as borders for dividing the display into distinct areas.

- If is necessary to display a static image, try to use colors that are symmetric to the middle

grey level at the boundary of two different colors, and slightly shift the borders line once in a while.

- Try to utilize medium gray hues for those areas that will have prolonged display times or

remain static as other menu elements change.

Can I Reverse This Effect?

Unlike the usually irreversible “burn-in” effects commonly associated with direct view phosphor display devices such as CRTs, an image retained on an LCD display can be reversed – often to a

point of total invisibility. However, the severity of the underlying causes (as described above) of the image retained on a specific display, as well as the variation factors (see “For Software Developers” above) under which the retained image was created, will dictate the final level of retention reversal.

One way to erase a retained image on a panel is to run the screen (monitor “on”) in an “all black” pattern for 4-6 hours. It is also helpful to do this in an elevated temperature environment of approximately 35º to 50ºC. Again, utilizing a dynamic screen saver with an all black background during prolonged idle display periods is a good way to avoid image retention issues.

Is My Display Warranted Against Image Sticking?

Image sticking is a phenomenon inherent to TFT LCD display technology itself, and as such, the occurrence of this “ghosting” effect is considered normal operation by the manufacturers of the LCD display modules which are integrated into today’s monitor solutions. As a result, 3M does not warrant any display against the occurrence of image sticking. We strongly advise that you follow the operating recommendations listed above under “For Monitor Operators” (above) as well as in the user manual for your display to prevent the occurrence of this phenomenon.

3M Touch Systems Technical Note

Product: LCD Monitors – Image Sticking

3M Touch Systems 3M Display & Graphics 300 Griffin Brook Park Drive Methuen, MA 01844 U.S.A. 1-866-407-6666 www.3M.com/touch

11/06

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3M Touch Systems Image Sticking

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