BASIC COMPUTER GRAPHIC DEVICES Display device 1. Cathode Ray Tube (CRT) Monitors These monitors employ the CRT technology to create a display. The CRT (also known as picture tube) receives the signals through a cable and the signal is decoded by the display controller which finally appears on a phosphor screen

Types of CRT Display Devices DVST (Direct View Storage Tube) Calligraphic or Random Scan display system Refresh and Raster Scan display system

DVST-Direct View Storage Tube A slow moving electron beam draw a line on the screen Screen has a storage mesh in which the phosphor is embedded Image is stored as a distribution of the charges on the inside surface of the screen Limited interactive support Storage Tube- it is a CRT with a long persistence phosphor i.e.. Provides flicker-free display No refreshing

DVST- Drawback Modifying any part of the image requires redrawing the entire modified image Change in the image requires to generate a new charge distribution in the DVST Slow process of drawing typically a few seconds are necessary for a complex picture Erasing takes about 0.5 seconds. All lines and characters must be erased No animation possible with DVSTnecessary

CALLIGRAPHIC or RANDOM SCAN DISPLAY SYSTEM Also called Vector, Stroke, Line Drawing displays Characters are also made of sequences of strokes (or short lines) Vectored electron beam is deflected from end-point to end-point Random scan order of deflection is dictated by the arbitrary order of the display commands Phosphor has short persistence decays in 10 100 s. The Display must be refreshed at regular intervals minimum of 30Hz (fps) for flicker-free display Refresh Buffer memory space allocated to store the display list or Display program for the display processor to draw the picture The display processor interprets the commands in the refresh buffer for plotting The display processor must cycle through the display list to refresh the phosphor The display program has commands for point-, line-, and character-plotting

2. LCD and FLAT PANEL DISPLAYS

LCD is made up of 6 layers vertical polarizer plane; layer of thin grid wires; layer ofLCDs; layer of horizontal grid wires; horizontal polarizer; and finally a reflector. LCD material is made up of long crystalline molecules; When the crystals are in an electricfield, they all line up in the same direction. Active matrix panels have a transistor at each grid point (X, Y). Crystals are dyed up toprovide color. Transistors act as memory, and also cause the crystals to change their statequickly. LCD displays are low cost, low weight, small size and low power consumption The display contains two polarizers, aligned 900 to each other. With the display in its OFF (or twisted) state, light entering the display is plane polarizedby the first polarizer. This polarized light passes through the liquid crystal sandwich and then through thesecond polarizer and is reflected back to the display. Turning the pixel ON (by applying and electric field) causes the crystal to untwist. Light now passing through the liquid crystal sandwich is now absorbed by the secondpolarizer. The pixel now appears dark. Displays are of two types plasma/gas discharge or Electroluminescent. All flat panel displays are raster refresh displays. A flat CRT is obtained by initially projecting the beam parallel to the screen and thenreflecting it through 900. Reflection of the electron beam reduces the depth of the CRT bottle and hence the display. Plasma displays like LCDs are also called active matrix displays. The required voltage or current to control the pixel illumination is supplied using a thinfilmtransistor or diode

3. LED Monitors

In the previous decade, the display technology has changed significantly. LED displays are one of the latest developments

In this field. LED monitors use light emitting diodes that acts as a performance booster in the monitors. Basically LED monitors are the LCD monitors with a LED backlight to power up the LCD panel. It means that LEDs are placed behind or around the LCD panel to enhance the luminosity and video definition of the monitor screen.As we have seen in the above section of LCD monitors, they use a cold cathode light as backlight. In the LED monitors all the concepts are same except this backlight, which is replaced by LEDs.There are three different types of LED monitors available based on the manner how the diodes are arranges in the monitor. These are Direct LEDs, Edge LEDs and RGB LEDs. Both Edge and Direct LED display monitors use white diodes that are used to illuminate the LCD panel to produce the improved picture quality. The arrangement of LEDs in the monitor is shown in the below image:In the Direct LEDs display, white diodes are placed all over the panel to produce higher quality image while the Edge LEDs display uses LEDs only on the borders of the LCD panel. Direct LEDs are generally used in the production of high definition TV whereas the Edge LEDs is mainly used in the production of computer screens. RGB LEDs display is better among the three types of LED monitors as it uses red, green and blue diodes to produce the lifelike images with amazing contrast ratio.

INPUT OUTPUT DEVICE An input device sends information to a computer system for processing, and an output device reproduces or displays the results of that processing. Depending on the interaction, a device can be both; referred to as an input/output or I/O device.For example, as you can see in the image, a keyboard sends electrical signals (input). Those signals are then interpreted by your computer, and then displayed on a monitor as text (output). Then in the lower half, you can see a computer sending data to a printer that will be reproduced on a piece of paper (output).INPUT DEVICEAn input device, such as a computer keyboard or mouse, can send information (input) to the computer, but it cannot receive or reproduce information (output) from the computer.1. KEYBOARD In computing, a keyboard is a typewriter-style device, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches. Following the decline of punch cards and paper tape, interaction via teleprinter-style keyboards became the main input device for computers.A keyboard typically has characters engraved or printed on the keys and each press of a key typically corresponds to a single written symbol. However, to produce some symbols requires pressing and holding several keys simultaneously or in sequence. While most keyboard keys produce letters, numbers or signs (characters), other keys or simultaneous key presses can produce actions or execute computer commands.Despite the development of alternative input devices, such as the mouse, touchscreen, pen devices, character recognition and voice recognition, the keyboard remains the most commonly used device for direct (human) input of alphanumeric data into computers.In normal usage, the keyboard is used as a text entry interface to type text and numbers into a word processor, text editor or other programs. In a modern computer, the interpretation of key presses is generally left to the software. A computer keyboard distinguishes each physical key from every other and reports all key presses to the controlling software. Keyboards are also used for computer gaming, either with regular keyboards or by using keyboards with special gaming features, which can expedite frequently used keystroke combinations. A keyboard is also used to give commands to the operating system of a computer, such as Windows' Control-Alt-Delete combination, which brings up a task window or shuts down the machine. A command-line interface is a type of user interface operated entirely through a keyboard, or another device doing the job of one.

2.MOUSE In computing, a mouse is a pointing device that detects two-dimensional motion relative to a surface. This motion is typically translated into the motion of a pointer on a display, which allows for fine control of a graphical user interface.Physically, a mouse consists of an object held in one's hand, with one or more buttons. Mice often also feature other elements, such as touch surfaces and "wheels", which enable additional control and dimensional input.

OUTPUT DEVICEAn output device, such as computer speakers or a projector can receive information (output) from the computer, but it cannot send information (input) to the computer.Types of PrintersSince the invention of the printing technology, a variety of technologies have been employed in computer printers. Broadly printers are categorized as impact and non impact printers. Impact printers are the type of printers in which a key strikes the paper to make a letter. The examples of Impact printers are Daisy wheel and Dot matrix printers. While non-impact printers do not operate by striking a head against a ribbon. Inkjet printers and laser printers are the non-impact printers. The most popular printers are described.Dot Matrix PrintersIt is a popular computer printer that prints text and graphics on the paper by using tiny dots to form the desired shapes. It uses an array of metal pins known as printhead to strike an inked printer ribbon and produce dots on the paper. These combinations of dots form the desired shape on the paper. Generally they print with a speed of 50 to 500 characters per second as per the quality of the printing is desired. The quality of print is determined by the number of pins used (varying from 9 to 24).The key component in the dot matrix printer is the printhead which is about one inch long and contains a number of tiny pins aligned in a column varying from 9 to 24. The printhead is driven by several hammers which force each pin to make contact with the paper at the certain time. These hammers are pulled by small electromagnet (also called solenoids) which is energized at a specific time depending on the character to be printed.The timings of the signals sent to the solenoids are programmed in the printer for each character.The printer receives the data from the computer and translates it to identify which character is to be printed and the print head runs back and forth, or in an up and down motion, on the page and prints the dots on the paper.

Laser Printers

Laser printers are the most popular printers that are mainly used for large scale qualitative printing. They are among the most popularly used fastest printers available in the market. A laser printer uses a slight different approach for printing. It does not use ink like inkjet printers, instead it uses a very fine powder known as Toner. Componetns of a laser printer is shown in the following imagehe control circuitry is the part of the printer that talks with the computer and receives the printing data. A Raster Image Processor (RIP) converts the text and images in to a virtual matrix of dots. The photoconducting drum which is the key component of the laser printer has a special coating which receives the positive and negative charge from a charging roller. A rapidly switching laser beam scans the charged drum line by line. When the beam flashes on, it reverses the charge of tiny spots on the drum, respecting to the dots that are to be printed black. As soon the laser scans a line, a stepper motor moves the drum in order to scan the next line by the laser. A developer roller plays the vital role to paste the tonner on the paper. It is coated with charged tonner particles. As the drum touches the developer roller, the charged tonner particles cling to the discharged areas of the drum, reproducing your images and text reversely. Meanwhile a paper is drawn from the paper tray with help of a belt. As the paper passes through a charging wire it applies a charge on it opposite to the toners charge. When the paper meets the drum, due to the opposite charge between the paper and toner particles, the toner particles are transferred to the paper. A cleaning blade then cleans the drum and the whole process runs smoothly continuously. Finally paper passes through the fuser which is a heat and presser roller, melts the toner and fixes on the paper perfectly

GRAPHIC CARDThe graphics components are the part of your computer that control and enhance how graphics (pictures, videos, programs, animation, 3D) are displayed on your computer screen. Often, the graphics components are on a separate card that plugs into a slot on the motherboard, which is the main part of the computer. That's why the graphics components are commonly called the graphics card. Sometimes the graphics card components are build directly into the motherboard