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Wednesday, July 6, 2011

How could an LCD display be blurry or out of focus?

Look around, more users than ever have Liquid Crystal Displays (LCDs), not Cathode Ray Tube (CRT) displays on their desks. These desktop versions of laptop LCD displays use less power than a CRT display of the same size, and provide high-contrast and brilliant color images all in a slim, high-tech package.

Just as features and styles vary from vendor to vendor, the appearance and quality of the displays will also differ. But if you have a new flat screen display that does not appear to be as sharp and clear as the CRT or older LCD it replaced, take a moment to check the basic settings. For the best possible video display, you will have to check both your computer's display settings and the flat panel display settings.

CRT Display

[caption id="attachment_239" align="alignnone" width="200" caption="Close up views of text displayed on a CRT (top) and LCD (bottom)"]LCD Display[/caption]

Native mode
Make sure the computer's display settings are set to the maximum resolution the flat panel screen supports. The maximum resolution of the flat panel display is called the "Native Mode" of the display, and will provide the clearest, sharpest possible match between the physical configuration of the LCD panel and your video card's signal.Early LCD displays had a single group of one red, green, and blue dots or pixels physically in the display that could be addressed by the display adapter in the computer. If a flat screen display had 1920 groups of RGB elements across the display and 1080 elements from top to bottom, then the native resolution of the display is 1920x1080. (This is also the current highest HDTV broadcast standard and may be identified as 1080i - for interlaced, or 1080p for progressive scan.)

When you set the video display for any resolution other than 1920x1080, the number of elements being displayed does not match the number of elements physically available in the screen. This results in a jagged or blocky appearing image on your screen. Lower resolution settings must either average the missing pixels, or ignore some of the data entirely; this can result in missing lines, or choppy-looking text in the worst case scenario.

Every flat panel screen has an optimal resolution where the image will appear the sharpest. Refer to your documentation for this resolution, and then adjust your display properties to this setting. If the Plug-and-play detection is supported and working properly between your system and the display, Windows will usually limit the maximum supported resolution to the native mode of your monitor.

Flat panel display adjustments
If the video display adapter properties are already set to the optimal mode for the display, and the image still appears blurry or out of focus, then the problem is most likely that the flat panel display is out of adjustment. While you could manually alter the display width, height, horizontal and vertical position of the image, most displays have an automatic adjustment feature.

A flat screen monitor will have several adjustments that you can make using the buttons or on-screen-display (OSD) menus. While many of the displays now auto-configure to your video signal when powered on or when the settings change, not all of the displays will. You should be aware that this feature is not tied to any one manufacturer, price range, or screen size.

Even if a display does not auto-configure automatically, most will have this feature available in the On-Screen-Display menus, where you can manually start the process. The auto configure feature should adjust the display width and height out to the physical edges of the display. There is no wasted space on an LCD display unlike a CRT that uses a shadow mask or where the picture tube extends behind the plastic bezel of the screen. "Auto Adjust" may also change your backlight brightness, display contrast, and color correction from the available display settings supported.

While it does not directly affect the sharpness, flicker can be annoying in your display. Refresh rates of 60 Hertz and less are the most common reason for flicker. Whether you have a choice in adjusting this may be a limitation of the display adapter, the flat panel monitor, or both. Some flat panel monitors only operate at a 60Hz refresh rate, however most new displays can support 70, 72, or 75Hz refresh rates. But it is your video adapter that must produce the signal for the monitor, and this is what must be adjusted to the higher refresh rate to benefit.

In Windows XP, enter Display properties from the control panel or by right-clicking on the desktop and selecting "properties", click on the "properties" tab then click on "advanced". Examine the monitor settings for refresh rate, although this should have been tied to the Plug-And-Play capabilities when the monitor was detected. You can try adjusting the refresh rate manually to see if this reduces flicker, although you may have to repeat the Auto-Adjust process if you make changes.

[caption id="attachment_240" align="alignnone" width="300" caption="All those colors blur together to make the background appear white to our eye. Under magnification, you can see not only the individual red, green, and blue sub-pixes of the LCD display, but also the blurring effect of font smoothing."]Screen zoom[/caption]

All those colors blur together to make the background appear white to our eye. Under magnification, you can see not only the individual red, green, and blue sub-pixes of the LCD display, but also the blurring effect of font smoothing.

ClearType is a software technology developed by Microsoft back in 2000 to enhance the appearance and readability of text on LCD displays. It is a standard feature in Windows XP, Vista and Windows 7 as well as specific applications like their Microsoft Reader (ebook) software. Like anti-aliasing, ClearType sacrifices sharpness (each pixel being on or off) and smooths the edges of fonts in an LCD display by addressing the individual red, green, or blue sub-pixels. (Anti-aliasing can only smooth edges at the pixel level, so all red, green, and blue components of the pixels would be affected.) Read more about ClearType on the Microsoft site; search for "ClearType" or go to http://www.microsoft.com/typography/cleartypeinfo.mspx

Windows does not automatically turn on its ClearType feature to smooth the edges of fonts. When using a CRT, where the pixel groups are typically much smaller than the display resolution, "Standard" smoothing will make your display more readable. But with an LCD Display, ClearType should make a big difference in readability.

ClearType under Windows XP:

1. To enable ClearType under Windows XP open display properties from the Control Panel or by right-clicking on your desktop.

Appearance menu

2. Select the Appearance tab, and click on the Effects button.

Appearance tab

3. Select ClearType for font smoothing if you have an LCD display.
4. Click OK to save changes in each window.

ClearType under Windows 7:

1. Open Display properties from the Control Panel.

Display properties

2. In the navigation bar, look for Adjust ClearType text; click on the link to launch the ClearType Text Tuner wizard.

ClearType Text Tuner Wizard

3. If you use an LCD screen, make sure there is a check in the Turn on ClearType box. Click Next.

Turn on Clear Type

4. Windows 7 should check to make sure your display is set to the native resolution of the LCD monitor. Click Next.

Select native resolution

5. The ClearType Text Tuner will display four screens of text to compare. In each screen, choose the box that looks sharpest to you. NOTE: If you have not done an auto-adjust of your monitor, do this before choosing from the screens. You can always repeat this process at any time if you think the screen still looks bad, or turn off ClearType at the first screen. Click Next to complete each selection, then click Finish when done.

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