INTRODUCTION

DISCUSSION ON : Video, Display Devices, CRT, LCD display devices, Raster-Scan and Random-Scan Systems, Graphics, Monitors and Workstations, Input devices, keyboard, mouse, trackball, data glove, scanners and Hard Copy Devices, Graphics Software. 

 

 

 

COMPUTER GRAPHICS

 

* Computer graphics refers to the creation, storage and manipulation of pictures and drawings

using a digital computer. 

 

* A major application of computer graphics is designing, particularly engineering and

architectural systems.

 

 

Graphic hardware can be divided into three major categories of devices: (1) Input devices

with which the user interacts to generate necessary instruction or data for creating graphics

(2) Display systems where the graphics are rendered on the monitor screen (3) Hardcopy

devices or printers through which the tangible graphics output is produced.

 

Based on the logical interaction types the input devices can be broadly classified as –

(1) locator device such as graphics tablet, touch panel, mouse, trackball, joystick, keyboard

that indicates a position (e.g., point coordinate) or orientation, (2) pick device such as the

light pen, joystick, mouse that can select a graphical object, (3) valuator device such as

joystick or trackball that are used to input scalar values such as rotation angle, scale factors

etc. (4) keyboard or text input device and (5) choice device such as the keyboard function

keys, mouse, touch panel, voice systems that are used to select menu options. This unit

deals exclusively with various input devices with different functional capabilities.

 

 

Keyboard

With a keyboard, a person can type a document, use keystroke shortcuts, access menus,

play games and perform a variety of other tasks. Though keyboards can have different

keys depending on the manufacturer, the operating system that they are designed for, and

whether they are attached to a desktop computer or are part of a laptop most keyboards

have between 80 and 110 keys, including:

• Typing keys (letters A to Z, a to z, characters like < , ? + = etc.)

• A numeric keypad (numbers 0 to 9, characters like ! @ # ( ) etc.) 

• Function keys (F1 to F12)

• Control keys (Ctrl, Alt, Del, Pg Up, Pg Dn, Home, End, Esc, Fn, arrow keys etc.) 

 

Function keys allow users to enter frequently-used operations with a single keystroke

and Control keys allow cursor and screen control. Displayed objects and menus can be

selected using the Control keys. 

 

A keyboard is a lot like a miniature computer. It has its own processor, circuitry (key

matrix) and a ROM storing the character map. It uses a variety of switch technology.

 

Though the basic working technology is same there are design variations to make the

keyboards easier and safer to use, versatile and elegant. Some of the non-traditional keyboards

are Das keyboard, Virtual Laser keyboard, True-touch Roll-up keyboard, Ion Illuminated

keyboard, and Wireless keyboard.

 

 

 

Mouse

A mouse is a hand-held pointing device, designed to sit under one hand of the user and to

detect movement relative to its two-dimensional supporting surface. It has become an

inseparable part of a computer system just like the keyboard. A cursor in the shape of an

arrow or cross-hair always associated with a mouse. We reach out for the mouse whenever

we want to move the cursor or activate something or drag and drop or resize some object

on display. Drawing or designing figures and shapes using graphic application packages

like AutoCAD, Photoshop, CorelDraw, and Paint is almost impossible without mouse.

 

The mouse’s 2D motion typically translates into the motion of a pointer on a display. In

a mechanical mouse a ball – roller assembly is used; one roller used for detecting X direction

motion and the other for detecting Y direction motion. An optical mouse uses LED and

photodiodes (or optoelectronic sensors) to detect the movement of the underlying surface,

rather than moving some of its parts as in a mechanical mouse. Modern Laser mouse uses

a small laser instead of a LED.

 

A mouse may have one, two or three buttons on the top. Usually clicking the primary or

leftmost button will select items or pick screen-points, and clicking the secondary or rightmost

button will bring up a menu of alternative actions applicable to the selected item or specific

to the context. Extra buttons or features are included in the mouse to add more control or

dimensional inputs.

 

 

Trackball

A trackball is a pointing device consisting of a ball housed in a socket containing sensors to

detect rotation of the ball about two axes—like an upside-down mouse with an exposed

protruding ball. The user rolls the ball with his thumb, fingers, or the palm of his hand to

move a cursor. A potentiometer captures the track ball orientation which is calibrated with

the translation of the cursor on screen. Tracker balls are common on CAD workstations

for ease of use and, before the advent of the touchpad, on portable computers, where there

may be no desk space on which to use a mouse.

 

 

Joystick

A joystick is used as a personal computer peripheral or general control device consisting of

a hand-held stick that pivots about the base and steers the screen cursor around. Most

joysticks are two-dimensional, having two axes of movement (similar to a mouse), but

three-dimensional joysticks do exist. A joystick is generally configured so that moving the

stick left or right signals movement along the X-axis, and moving it forward (up) or back

(down) signals movement along the Y-axis. In joysticks that are configured for three-

dimensional movement, twisting the stick left (counter-clockwise) or right (clockwise)

signals movement along the Z-axis. In conventional joystick potentiometers, or variable

resistors, are used to dynamically detect the location of the stick and springs are there to

return the stick to centre position as it is released.

 

In many joysticks, optical sensors are used instead of analog potentiometer to read

stick movement digitally. One of the biggest additions to the world of joysticks is force

feedback technology. On using a force feedback (also called haptic feedback) joystick if

you’re shooting a machine gun in an action game, the stick would vibrate in your hands. Or

if you crashed your plane in a flight simulator, the stick would push back suddenly which

means the stick moves in conjunction with onscreen actions.

 

Joysticks are often used to control games, and usually have one or more push-buttons

whose state can also be read by the computer. Most I/O interface cards for PCs have a

joystick (game control) port. Joysticks were popular during the mid-1990s for playing

games and flight-simulators, although their use has declined with promotion of the mouse

and keyboard.

 

 

 

Printer

The printer is an important accessory of any computer system, specially for a graphics

system. This is because most of the graphics creation using computer graphics has its

ultimate utilization in printed form – for documentation, exhibition or publication in print

media or books. It is the quality of printed output that finally matters in many businesses.

Based on the available printing technology the major factors which control the quality

of printer are individual dot size on the paper and number of dots per inch (dpi). Clearly, the

lesser the size of the dots the better the detail of the figure reproduced. Higher dpi values

increase the sharpness and detail of a figure and enhance the intensity levels that a printer

supports. Other important factors for selection of a printer are printing speed and print area

or printer memory

 

 

Impact vs. Non-impact

There are several major printer technologies available. These technologies can be broken

down into two main categories with several types in each: 

 

• Impact: These printers have a mechanism whereby formed character faces are

pressed against an inked ribbon onto the paper in order to create an image. For

example, dot matrix printer and line printer. 

 

• Non-impact: These printers do not touch the paper rather use laser techniques, ink

sprays, xerographic processes and electrostatic methods to produce the image on

paper. For example, laser printer, inkjet printer, electrostatic printer, drum plotter,

flatbed plotter.

 

 

Dot Matrix Printer

A dot matrix printer refers to a type of computer printer with a print head (usually containing

9 to 24 pins) that runs back and forth on the page and prints by impact, striking an ink

soaked cloth ribbon against the paper, much like a typewriter. Unlike a typewriter or daisy

wheel printer, letters are drawn out of a dot matrix, and thus, varied fonts and arbitrary

graphics can be produced. Because the printing involves mechanical pressure, these printers

can create carbon copies. The print head normally prints along every raster row of the

printer paper and the color of print is the color of the ink of the ribbon.

 

Each dot is produced by a tiny yet stiff metal rod, also called a ‘wire’ or ‘pin’, which

is driven forward by the power of a tiny electromagnet or solenoid, either directly or

through small levers (pawls). The pins are usually arranged vertically where marginal offsets

are provided between columns to reduce inter-dot spacing. The position of pins in the print

head actually limits the quality of such a printer.

 

Hardware improvements to dot matrix printers boosted the carriage speed, added more

(typeface) font options, increased the dot density (from 60dpi up to 240dpi), and added

pseudo-colour printing through multi-colour ribbon. Still such printers lack the ability to

print computer-generated images of acceptable quality. It is good for text printing in

continuous sheets.

 

Strictly speaking, ‘dot matrix’ in this context is a misnomer, as nearly all inkjet, thermal,

and laser printers produce dot matrices. However, in common parlance these are seldom

called ‘dot matrix’ printers, to avoid confusion with dot matrix impact printers.

 

 

Line Printer

The line printer is a form of high speed impact printer in which a line of type is printed at a time.

In a typical design, a fixed font character set is engraved onto the periphery of a

number of print wheels, the number matching the number of columns (letters in a line).

The wheels spin at high speed and paper and an inked ribbon are moved past the print position. As the desired character for each column passes the print position, a hammer strikes the paper and ribbon causing the desired character to be recorded on the continuous

paper. Printed type is set at fixed positions and a line could consist of any number of

character positions with 132 columns as the most common, but 80 column, 128 column

and 160 column variants are also in use. Other variations of line printer have the type on

moving bars or a horizontal spinning chain.

The line printer technology is usually both faster and less expensive (in total ownership)

than laser printers. It has its use in medium volume accounting and other large business

applications, where print volume and speed is a priority over quality. Because of the limited

character set engraved on the wheels and the fixed spacing of type, this technology was

never useful for material of high readability such as books or newspapers.

 

 

 

Inkjet Printer

An inkjet printer is a non-impact printer that places extremely small droplets of ink onto the

paper to create an image. These printers are popular because they less costly but generate

attractive graphic output.

The dots sprayed on paper are extremely small (usually between 50 and 60 microns in

diameter), and are positioned very precisely, with resolutions of up to 1440 × 720 dpi. The

dots can have different colours combined together to create photo-quality images.

The core of an inkjet printer is the print head that contains a series of nozzles that are

used to spray drops of ink. The ink is contained in ink cartridges that come in various

combinations, such as separate black and colour cartridges, or a cartridge for each ink

colour. A stepper motor moves the print head assembly (print head and ink cartridges) back

and forth across the paper. The mechanical operation of the printer is controlled by a small

circuit board containing a microprocessor and memory.

There are two main inkjet technologies currently used by printer manufacturers. 

 

• Thermal bubble (or bubble jet): This is used by manufacturers such as Canon and

Hewlett Packard. In a thermal inkjet printer, tiny resistors create heat, and this heat

vaporizes ink to create a bubble. As the bubble expands, some of the ink is pushed

out of a nozzle onto the paper. When the bubble ‘pops’ (collapses), a vacuum is

created. This pulls more ink into the print head from the cartridge. A typical bubble

jet print head has 300 or 600 tiny nozzles, and all of them can fire a droplet

simultaneously. 

 

• Piezoelectric: Patented Epson, this technology uses piezo crystals. A crystal is

located at the back of the ink reservoir of each nozzle. The crystal receives a tiny

electric charge that causes it to vibrate. When the crystal vibrates inward, it forces

a tiny amount of ink out of the nozzle. When it vibrates out, it pulls some more ink

into the reservoir to replace the ink sprayed out.

 

 

 

Laser Printer

The laser printer employs technology similar to that of a photocopy machine. A laser beam

focuses a positively charged selenium-coated rotating drum. The laser gun removes the

positive charge from the drum except for the area to be printed (black portion of the

paper). In this way, the laser draws the letters and images to be printed as a pattern of

electrical-charges — an electrostatic image. The negatively-charged black toner powder

first adheres to this positively-charged area (image) on the drum from where it is transferred

to the rolling white paper. Before the paper rolls under the drum, it is given a positive charge

stronger than the positive charge of the electrostatic image, so the paper can pull the toner

powder away. The paper is then subjected to mild heating to melt and fix the loose toner on

the paper. The laser printer is mainly a bilevel printer. In case of colour lasers, this process

is repeated three times.

For the printer controller and the host computer to communicate, they need to speak the

same page description language. The primary printer languages used nowadays are Hewlett

Packard’s Printer Command Language (PCL) and Adobe’s Postscript. Both these languages

describe the page in vector form — that is, as mathematical values of geometric shapes,

rather than as a series of dots (a bitmap image). Apart from image data the printer controller

receives all of the commands that tell the printer what to do — what paper to use, how to

format the page, how to handle the font, etc. Accordingly the controller sets the text margins,

arranges the words and places the graphics. When the page is arranged, the raster image

processor (RIP) takes the page data, either as a whole or piece by piece, and breaks it down

into an array of tiny dots so the laser can write it out on the photoreceptor drum. In most

laser printers, the controller saves all print-job data in its own memory. This lets the controller

put different printing jobs into a queue so it can work through them one at a time.

 

 

Electrostatic Printer

In inkjet printers, the single printing head moves left-to-right and prints as it is traveling. In

contrast, the electrostatic printer has many print heads, actually covering the entire 36"

media width. So instead of a single print head moving across the width of the media, the

electrostatic printer prints an entire width of the page at one time. The media (paper,

vellum, film) is electrostatically charged (energized). The toner solution is circulated past

the media and ‘sticks’ to the energized portion of the media, thus producing a very fast

high quality image.

The printer creates colour prints by breaking colour data down into three basic colours

(cyan, magenta, and yellow) plus black, and printing one colour at a time. In 5-pass print

mode, combinations of cyan, magenta, yellow and black provide a wide range of different

colours. Using the registration marks printed during the preliminary registration pass ensures

that the colour plot is beautiful with no misalignment.

 

 

Plotter

In contrast to the printer which is primarily a raster scan device, the plotter is a vector

device. In colour plotters the carriage accommodates a number of pens with varying colours

and widths. The microprocessor in the plotter receives instructions from the host computer

and executes commands like ‘move’ (moving the carriage to a given position with pens up)

and ‘draw’ (drawing geometric entities like point, line, arc, circle etc. with pens down).

Since the plotter is a vector device it can directly reach specific positions on printer paper

without following raster row sequence. In flat bed plotter the paper lies flat and stationary

while the pen moves from one location to another on the paper. But in drum plotters the

paper itself slides on a cylindrical drum and the pen moves over the drum.

 

 

 

VIDEO

Just like text, audio and still image digital videos are also a powerful elements of multimedia

systems. To understand how digital video is used as a media we need to understand some

fundamental aspects of analog video technology. 

 

Basically video or motion pictures are created by displaying images depicting progressive

stages of motion at a rate fast enough so that the projection of individual images overlap on

the eye. Persistence of vision of human eye, which allows any projected image to persist

for 40–50 ms, requires a frame rate of 25–30 frames per second to ensure perception of

smooth motion picture.

 

In a video display:

• Horizontal resolution is the number of distinct vertical lines that can be produced in a frame.

• Vertical resolution is the number of horizontal scan lines in a frame.

• Aspect ratio is the width-to-height ratio of a frame.

• Interface† ratio is the ratio of the frame rate to the field rate. 

 

Constitution-wise there are three types of video signals: Component video, Composite

video and S-video. Most computer systems and high-end video systems use component

video whereby three signals R, G and B are transmitted through three separate wires

corresponding to red, green and blue image planes respectively. 

 

However, because of the complexities of transmitting the three signals of component

video in exact synchronism and relationship these signals are encoded using a frequency

interleaving scheme into a composite format that can be transmitted through a single

cable. Such format known as composite video, used by most video systems and

broadcast TV, uses one luminance and two chrominance signals. Luminance (Y) is a

monochrome video signal that controls only the brightness of an image. Chrominance

is actually two signals (I and Q or U and V), called colour differences (B–Y, R–Y) and

contains colour information of an image. Each chrominance component is allocated

half as much band width as the luminance, a form of analog data compression,

which is justified by the fact that human eyes are less sensitive to variations in colour

than to variations in brightness. Theoretically, there are infinite possible combinations

(additive) of R, G, B signals to produce Y, I, Q or Y, U, V signals. The common CCIR

601 standard defines — 

 

Luminance (Y) = 0.299R + 0.587 G + 0.114B

Chrominance (U) = 0.596R – 0.247 G – 0.322B

Chrominance (V) = 0.211R – 0.523G + 0.312B

 

The inverse of the above transformation formula gives

 

Red (R) = 1.0 Y + 0.956 U + 0.621 V

Green (G) = 1.0 Y − 0.272 U − 0.647 V

Blue (B) = 1.0 Y − 1.061 U − 1.703 V

 

Unlike composite video, S-video (separated video or super video as S –VHS) uses two

wires, one for luminance and another for a composite chrominance signal. Component

video gives the best output since there is no cross-talk or interference between the different

channels unlike composite video or S-video. 

 

In a television transmission system, every part of every moving image is converted

into analog electronic signals and is transmitted. The VCR can store TV signal on magnetic

tapes, which can be played to reproduce stored images. There are three main standards for

analog video signals used in television transmission: NTSC, SECAM and PAL.

 

Digital Video

For video to be played and processed in computers it needs to be converted from analog to

digital representation. Video digitization is achieved just like audio digitization by sampling

the analog video signal at a preset frequency and subsequently quantizing the discrete

samples in digital format. This is done with the help of analog to digital converter or ADC.

There are two kinds of possible digitizations or digital coding–Composite coding and

Component coding. In composite coding, all signal components taken together as a whole

are converted into digital format. In component coding, each signal component is digitized

separately using different sampling frequency (13.5 MHz for luminance, 6.75 MHz for

chrominance).

Based on whether the ADC is inside a digital camera, or in an external unit or inside the

computer there can be three types of digital video systems – Digital Camera-based System,

External ADC System and Video Frame Grabber Card-based System. 

 

The main function of the video frame grabber card is to take the composite (luminance

chrominance) analog video signal, decode it to RGB signal, then convert it to the digital

format and store each frame first in the frame buffer on the card itself. At an adequate

frame-rate consecutive frames are streamed to the monitor, routed through the frame

buffer of the main memory to present live video on the computer screen. The Sun video

digitizer from Sun Microsystems captures NTSC video signal (RGB) with frame resolution

of 320 × 240 pixels, quantization of 8 bits/pixels and a frame rate of 30 frames per second.

How closely the digital video approximates the original analog video depends on the sampling

resolution or number of bits used to represent any pixel value.

 

Advantages of Digital Video

1. Storing video on digital devices memory ready to be processed, (noise removal,

cut and paste, size and motion control and so on) and integrated into various

multimedia applications is possible.

2. It allows direct access, which makes non-linear video editing (audio mixing,

adding text, titles and digital effects etc.) simple.

3. It allows repeated recording without degradation of image quality.

4. Ease of encryption and better tolerance to channel noise is possible.