Distinguish Between the Different Display Devices and Their Characteristics

Distinguish between the different display devices and their characteristics

Projectors, CRT and LCD

Projector

A video projector takes a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright light to project the image, and most modern ones can correct any curves, blurriness, and other inconsistencies through manual settings. Video projectors are widely used for conference room presentations, classroom training, and home theatre applications.

Common display resolutions for a portable projector include SVGA (800×600 pixels), XGA (1024×768 pixels), and 720p (1280×720 pixels).

A Projector can be connected to a PC in many ways ie: HDMI, Component Video, VGA, DVI, Composite Video (RCA), S-Video, RS-232

CRT

The CRT or cathode ray tube, is the picture tube of a monitor. The back of the tube has a negatively charged cathode. The electron gun shoots electrons down the tube and onto a charged screen. The screen is coated with a pattern of dots that glow when struck by the electron stream.

Each cluster of three dots, one of each color, is one pixel.

The image on the monitor screen is usually made up of at least tens of thousands of such tiny dots glowing on command from the computer. The closer together the pixels are, the sharper the image on the screen. The distance between pixels on a computer monitor screen is called its dot pitch and is measured in millimeters. Most monitors have a dot pitch of .28 mm or less.

A modern CRT display has considerable flexibility: it can usually handle a range of resolutions from 320 by 200 up to 2560 by 2048 pixels.

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LCD

A liquid crystal display (commonly abbreviated LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector.

• Resolution: unlike CRT monitors, LCD monitors have a native-supported resolution for best display effect.
• Dot pitch: the granularity of LCD pixels. The smaller, the better.
• Viewable size: The length of diagonal of an LCD panel
• Input ports: (e.g. DVI, VGA, or even S-Video).

LCD technologies

Resolution (e.g. XGA, SXGA+, UXGA, WUXGA)

The resolution of a monitor indicates how densely packed the pixels are. In general, the more pixels (often expressed in dots per inch), the sharper the image. Most modern monitors can display 1024 by 768 pixels, the SVGA standard. Some models can display 1280 by 1024, or even 1600 by 1200 and higher.

XGA: (eXtended Graphics Array) XGA supports a resolution of 1024 x 768 pixels with a palette of 256 colors, or 640 x 480 with high color (16 bits per pixel). XGA-2 added 1024 x 768 support for high color and higher refresh rates, improved performance, and supports 1360 x 1024 in 16 colors.

SXGA+: (Super eXtended Graphics Array) Is commonly used on 14-inch or 15-inch laptop LCD screens with a resolution of 1400 × 1050 pixels. SXGA+ is also the maximum resolution native to many high-end video projectors.

UXGA: (Ultra eXtended Graphics Array) A standard monitor resolution of 1600 × 1200 pixels.

WUXGA: Stands for Widescreen Ultra eXtended Graphics Array and is a display resolution of 1920 × 1200 pixels with a 16:10 screen aspect ratio. It is a wide version of UXGA, and is appropriate for viewing North American HDTV, which uses a 1920 × 1080 image at a 16:9 ratio.

The 16:10 aspect ratio (as opposed to the 16:9 used in widescreen televisions) was chosen because this aspect ratio is appropriate for displaying two full pages of text side by side. It also allows viewing of 16:9 video on a computer with player controls visible.

Connector types

Video Card Outputs, from left to right. VGA, S-Video and DVI

VGA

The common 15-pin VGA connector found on most video cards, computer monitors, and other devices is almost always used solely to carry analog component video signals. Used mostly for CRT monitors, but many LCD monitors also use these connectors.

The common 15-pin VGA connector found on most video cards, computer monitors, and other devices is almost universally called “HD-15”. HD stands for “high-density”. VGA connectors are almost always used solely to carry analog signals.

Mini VGA

A Mini-VGA connector is used on laptops and other systems in place of the standard VGA connector. Apart from its compact form, mini-VGA ports have the added ability to output both composite and S-Video in addition to VGA signals.

DVI

Digital Visual Interface (DVI) is a video interface standard designed to maximize the visual quality of digital display devices such as flat panel LCD computer displays and digital projectors.

As well as digital signals, the DVI connector also includes pins providing the same analog signals found on a VGA connector, allowing a VGA monitor to be connected with a simple plug adapter. This feature was included to make DVI universal, as it allows either type of monitor (analog or digital) to be operated from the same connector.

The connector also includes provision for a second data link for high-resolution displays, though many devices do not implement this. In those that do, the connector is sometimes referred to as DVI-DL (dual-link).

The DVI connector on a device is therefore given one of three names, depending on which signals it implements:

DVI-D (digital only)

DVI-A (analog only)

DVI-I (digital & analog)

HDMI

High-Definition Multimedia Interface (HDMI) is an all-digital audio/video interface capable of transmitting uncompressed streams. HDMI is compatible with High-bandwidth Digital Content Protection (HDCP) Digital Rights Management technology. HDMI provides an interface between any compatible digital audio/video source, such as a set-top box, a DVD player, a PC, a video game system, or an AV receiver, and a compatible digital audio and/or video monitor.

The standard Type A HDMI connector has 19 pins and is backward-compatible with the single-link Digital Visual Interface carrying digital video (DVI-D or DVI-I, but not DVI-A) used on modern computer monitors and graphics cards. This means that a DVI-D source can drive an HDMI monitor, or vice versa, by means of a suitable adapter or cable, but the audio and remote control features of HDMI will not be available.

Because most DVI PC-style displays do not have support for High-bandwidth Digital Content Protection (HDCP) on the display, the signal source may prevent the end user from viewing or especially copying certain restricted content.

S-Video

Separate video (S-Video) is an analog video signal that carries the video data as two separate signals (brightness and color), unlike composite video which carries the entire set of signals in one signal line. S-Video, as most commonly implemented, carries high-bandwidth 480i or 576i resolution video, i.e., standard definition video. It does not carry audio on the same cable.

S-Video is mostly used to output a PC’s video signal to a Television.

Component / RGB

Composite video is the format of an analog television (picture only) signal. It is used to output a PC’s video signal to a Television.

Settings

Refresh rate

The refresh rate is how many times per second the screen is refreshed (redrawn). The faster the refresh rate, the less the monitor will flicker.

On smaller CRT monitors (14″), few people notice any change above 6072 Hz. On larger CRT monitors (17″, 19″), most people would experience mild discomfort unless the refresh is set to a more comfortable 85 Hz or higher. 100 Hz is comfortable for most people.

LCD monitors do not suffer from the same problems as CRT monitors because the refresh rate does not mean the same. LCD monitors will provide excellent quality and resolution at 60Hz. The more important issue for an LCD monitor is its Response Time, Image Brightness, and Image Contrast Ratio.

Different operating systems set the default refresh rate differently. Windows 95 and Windows 98(SE) set the highest possible refresh rate. Windows NT based OS’s such as Windows 2000 and its descendant Windows XP, however, by default set the refresh rate to the lowest supported, usually 60 Hz.

Old monitors could be damaged if a user set the video card to a higher refresh rate than supported by the monitor. Nowadays most monitors would simply display a notice that the video signal uses an unsupported refresh rate.

To change the refresh frequency for your monitor:

1. Open Display in Control Panel.
2. On the Settings tab, click Advanced.
3. On the Monitor tab, in the Refresh Frequency list, click a new refresh rate.

Resolution

The resolution of a monitor indicates how densely packed the pixels are. In general, the more pixels (often expressed in dots per inch), the sharper the image. Most modern monitors can display 1024 by 768 pixels, the SVGA standard. Some models can display 1280 by 1024, or even 1600 by 1200 and higher.

To change your screen resolution:

1. Open Display in Control Panel.
2. On the Settings tab, under Screen resolution, drag the slider, and then click Apply.
3. When prompted to apply the settings, click OK. Your screen will turn black for a moment.
4. Once your screen resolution changes, you have 15 seconds to confirm the change. Click Yes to confirm the change; click No or do nothing to revert to your previous setting.