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COMPUTER MONITOR. Many of us sit in front of a computer monitor everyday. But how many of us think that how do computer monitors work??????
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Many of us sit in front of a computer monitor everyday. But how many of us think that how do computer monitors work?????? Video (from Latin:”I see”) is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion. The video display is the most used output device on a computer. The display provides instant feedback by showing you text and graphic images as you work or play. INTRODUCTION
Resolution refers to the number of individual dots of color, known as pixels, contained on a display. Standards and Resolution
Two measures describe the size of your display: the aspect ratio and the screen size. Aspect ratio For widescreen LCD monitors, the aspect ratio is 16:9 (or sometimes 16:10 or 15:9) means that the ratio of the width of the display screen to the height is 16 to 9. Viewable area For CRT monitors, screen size is measured diagonally from outside edges of the display casing. In other words, the exterior casing is included in the measurement as seen in fig. Aspect ratio and Viewable area
For LCD monitors, screen size is measured diagonally from the inside of the beveled edge. The measurement does not include the casing as indicated in the fig.
Connections • Analog VGA Connection • A video adapter is an expansion card or component that provides the ability to convert display information into a signal that is sent to the monitor. Once the display information is in analog form, it is sent to the monitor through a VGA cable.
Because a VGA (analog) connector does not support the use of digital monitors, the Digital Video Interface (DVI) standard was developed. II)DVI Connection The DVI specification is based on Silicon Image's Transition Minimized Differential Signaling (TMDS) and provides a high-speed digital interface. A transmitter on the video adapter sends the digital information to a receiver in the monitor. TMDS takes the signal from the video adapter
Touch-screen monitors Wireless monitors Television and HDTV Integration 3-D Display CRT Technology LCD Display Plasma Display Display Technologies
3-D Display Technology A 3D display prototype by Philips A 3D display is any display device capable of conveying three-dimensional images to the viewer.
What is CRT? CRT Technology Close-up of a color CRT. The cathode ray tube (CRT) is an evacuated glass envelope containing an electron gun (a source of electrons) and a fluorescent screen, usually with internal or external means to accelerate and deflect the electrons. When electrons strike the fluorescent screen, light is emitted.
How CRT Monitors Work? The cathode rays are known to be a beam of electrons emitted from a heated cathode inside a vacuum tube and accelerated by a potential difference between this cathode and an anode. The screen is covered with a phosphorescent coating (often transition metals or rare earth elements), which emits visible light when excited by high-energy electrons. The beam is deflected either by a magnetic or an electric field to move the bright dot to the required position on the screen. the entire front area of the tube is scanned systematically in a fixed pattern called a raster. Electron gun The source of the electron beam is the electron gun, which produces a stream of electrons through thermionic emission, and focuses it into a thin beam.
The advances made in CRT • One or more filament heaters within the electron gun. • Position of electron gun to be slightly off the axis. • The interior side of Phosphor layer covered with a layer of aluminum. A CRT monitor contains millions of tiny red, green, and blue phosphor dots that glow when struck by an electron beam that travels across the screen to create a visible image.
I) There are three ways to filter the electron beam in order to obtain the correct image on the monitor screen: shadow mask, aperture grill and slot mask. These technologies also impact the sharpness of the monitor's display. 1) Shadow-mask It is a thin metal screen filled with very small holes. CRT Features and Attributes Shadow mask close-up
2) Aperture-grill Monitors based on the Trinitron technology, which was pioneered by Sony, use an aperture-grill which consists of tiny vertical wires. However, aperture-grill displays are normally more expensive. Aperture grille close-up 3) Slot-mask It uses a combination of the shadow mask and aperture- grill technologies. Rather than the round perforations found in shadow-mask CRT displays, a slot-mask display uses vertically aligned slots.
The smaller and closer the dots are to one another, the more realistic and detailed the picture appears. II) Dot Pitch • an indicator of the sharpness of the displayed image. • The smaller the dot pitch, the sharper is the image. • How to measure dot pitch?
III) Refresh Rate • The number of times that the image on the display is drawn each second. • As high as possible. • Control flicker which lead to headaches and eye strain. • 1280x1024 at 85 Hertz or 1600x1200 at 75 Hertz are best possible recommendations for refresh rate and resolution.
Cheaper and that too offers higher resolutions on smaller screen On the other hand, worse color rendition of LCD due to fluorescent lights used as backlights. LCD<CRT< Future of CRT Technology POWER CONSUMPTION <Plasma • Adherents: • Computer gaming • Psychological research • Professional video, photography and graphics field • In UK, Dixons ceased selling CRT models in 2007. • Samsung ceased selling CRT models in 2008. • Cheaper alternative.
Electromagnetic Ionizing radiation Toxicity Flicker High voltage Implosion Health Concerns
One serious drawback of CRT is they are bulky. To increase the screen width, length of the tube needs to be increased. Consequently, any big-screen CRT television is going to weigh a ton and take up a sizable chunk of a room. The plasma flat panel display have wide screens, comparable to the largest CRT sets, but they are only about 6 inches (15 cm) thick. What is Plasma? Plasma is a gas made up of free-flowing ions (electrically charged atoms) and electrons (negatively charged particles). The plasma video display was co-invented in 1964 at the University of Illinois at Urbana-Champaign by Donald Bitzer, H. Gene Slottow, and graduate student Robert Willson for the PLATO Computer System. Plasma Display
Noble gases like Xenon and Neon atoms release ultraviolet light photons, which are invisible to the human eye. But ultraviolet photons can be used to excite visible light photons.
Screen Size: Up to 150” diagonally Total Thickness: Less than 4” Power Rating: 400W for 50” screen Lifetime: 27 years at 6 hours per day. This is the estimated time over which maximum picture brightness degrades to half the original value, not catastrophic failure. Contrast Ratio Claims: The difference between the brightest and darkest parts of an image, measured in discrete steps, at any given moment. Generally kept as high as 20,000:1. This is a significant advantage of plasma over other display technologies as the higher the contrast ratio, the more realistic the image is. Running a display at maximum brightness will significantly reduce the panel's lifespan. This typically still results in a brighter screen than CRT displays. General Characteristics
Screen burn-in An example of a plasma display that has suffered severe burn-in from stationary text The prolonged display of a menu bar or other graphical elements over time can create a permanent ghost-like image as the phosphor compounds which emit the light lose their luminosity with use.
Inside the Display • Xenon and Neon gas • The address electrodes • The transparent display electrodes
The computer charges the electrodes that intersect at the cell to ionize the gas in that cell. When the intersecting electrodes are charged, an electric current flows through the gas in the cell. When an ultraviolet photon hits a phosphor atom in the cell, one of the phosphor's electrons jumps to a higher energy level and it heats up. When the electron falls back to its normal level, it releases energy in the form of a visible light photon. The colors in the sub pixels blend together to create the overall color of the pixel. By varying the pulses of current flowing through the different cells, the control system can increase or decrease the intensity of each sub pixel color to create hundreds of different combinations of red, green and blue.
Large and very thin screen Brighter image Wide viewing angle The biggest drawback of this technology has been the very high price. Advantages Drawback
Dual Monitors • With two monitors, you can: • View large spreadsheets • Make changes to a web page's code on one monitor and view the results on the second • Open two different applications, such as a Word document on one monitor and your web browser on the second • Besides two displays and two sets of the appropriate video cables, the only thing needed is a video adapter with two display connections. You should also double-check your computer's operating system to be sure it supports the use of dual monitors. For example, Windows 98 SE, Me, 2000, and XP support multiple monitors.
