Applications Of Computer Graphics

• Computer Aided Design

mainly for the architectural and engineering designs

also in the industries such as the textile, automobiles, aircrafts, watercrafts, computer etc

the objects are first displayed in the wireframe outline that give the deigners the overall shape and the internal structure of the object Realtime animations using the wireframe displays are used for testing the performance of the vehicles and systems. They are used to determine how the vehicle operators are affected by the certain motions.

the architects use interactive graphics methods to lay out floor plans, such positioning of the windows, doors, shelves etc...

• Presentation Graphics

commonly used to summarize financial, statistical, mathematical, economic data for research purposes,managerial reports and other consumer information bulletin and other type of reports .

Typical examples are the bar charts, pie graphs, and the other displays showing the relation between multiple parameters. The three diamensional graphs can provide a more attractive and more effective presentation of the data relationships.

Time charts and the task network layouts are used in the project management to schedule and monitor the progress of the projects.

• Computer Art

used both in the fine art and commercial art applications. The artist use a variety of software as well as hardware products such as painbrush programs, the paintpackages, the prssure sensitive pens etc.

These methods are also used in commercial arts for the creating the logos and other designs, tv advertising spots etc.

Animations are also frequently used in the advertising and the tv commercials where they are created frame by frame, where each frame is rendered and saved as an image. In each successive frame the object motion is simulated by moving the object position slightly from the previous frame. A common graphics mehtod used in many commercials is morphing where one image is transformed into another

• Entertainment

computer graphics is commonly used in the making of motion pictures, motion videos, and television shows. Sometimes they are displayed themselves and sometimes they are combined with the actors and live scenes.

Music vidoes use the graphics in several ways, the objects can be combined with live action or the methods of image processing can be used to transform the person or objects into another.

• Education and Training

computer generated models of physical, financial and econoomic systems are often used as eduacttional aids.

For training applications, special systems are designed, examples of such systems are the simulators used for training the pilots, ship captions, heavy equipment operators, air traffic controll personnel.

Here a viewing screen with multiple panels is mounted in front of the simulator. The keyboard is used to input the parameters affecting the airplance performnance or the environment.

Automobile simulators are used to investigate the behaviour of the drivers in critical situations and then optimizing the vehicle design to maximize the traffic safety.

• Visualization

the scientist, engineers are often to deal with large amount of data that cannot be intrepreted in the numerical form, so once the graphs are plotted with the density values, we can see the overall pattern of the data.

It include both scientific( scientific, engineering, medical) and business visualization

colour coding is one way to visualize a data set.

• Image processing

the difference between computer graphics and image proceesing is that when CG is used to create picture, image processing is used to 1) improving the picture quality 2) machine perception of visual information, as in robotics.

To apply the process of image processing we first digitize the image into an image file and then digital methods can be applied to rearrange the picture parts and enhance the colour separations, improve the quality of the shading etc.

Medical applications also make an extensive use of image processing of techniques for picture enhancements, in tomography and in simualtions of operations.

Image processing and computer graphics are combined in various applications

• Graphical User Interface

all the software packages provide graphical user interface. A major component of GUI is window manager that allows userd to work in many windows simultaneously

interfaces also display the menus and icons for the fast selection of the processing options and the parameter values. The advantage of the icon is that it occupies less space in the screen than the textual description and can be well understood if well designed. The menus will containt the textual description and the icons.

Overview of Graphic Systems

Video Dispay Systems

The primary output device in a graphic system is a video monitor. Most of the monitors are based on the standard cathode ray tube(CRT) design, but several others design also exist.

Refresh Cathode Ray Tubes

A beam of electrons emitted by an electron gun, passes through a focusing and deflection systems that direct the beam to the specific postions in the phosphour coated screen. The phosphour coated screen emits a spot of light which fades very rapidly. One way to keep the phosphour glowing is to redraw the image repetedly by quickly directing the electron beam back over to the same position. This type of display is called refresh CRT

The primary components of the electron gun in the CRT are the heated metal cathode and as control grid. Heat is supplied to the cathode using a coil of wire called the filament and the electron are boiled of the cathode. They are accelarated to the phosphour coated screen using a high positive voltage which are free to navigate inside the vaccum in the CRT envelope. The accelrating is done either using a positive metal coating in the CRT envelope or the electron gun itself will contain the accelarating anode and the focusing system.

The intensity of the beam is controlled using a contrl grid which is a metal cylinder that fits over the cathode. A high negative voltage when applied to the control grid shut off the electron beam by repelling the electrons and stopping them from passing through the small hole at the end of the control grid structure. A smaller voltage simply decreases the number of electrons passing through it. Since the the amount of light emitted by the phosphour screen depends on the number of electrons striking the screen, we can control the brightness of the display by simply varying the voltage on the contol grid.

The focusing system of the CRT does the duty of converging the elcetron beam into a spot, otherwise as it approaches the screen, the electrons would repel each other and would scatter away. Focusing is accomplished using electric or the magnetic fields. In the electrostatic focusing the electron beam passes through a positivly charged metal cylinder that forms an electrostatic lens. It function exaclty as the optical lens does by focusing the beam at a particular focal distance. Magnetic focusing is accomplished by setting up a coil around the CRT envelope. Magnetic focusing produces the smallest spot size and is used in the case of special device purposes

Additional focusing system are provided in the high precision devices. The radius of curvature varies as we move from the screen centre to the edges and hence the distance electron beam has to travel varies. The system can adjust accoding to the screen position of the beam so that images to the edges are not blurd.

As the focusing and deflection of the beam has to be done either with electric or the magnetic fields, now CRTs usually come with two pairs of deflection coils one on top and bottom and the other on the sides of the tube. When it is done electrically, we have the deflection plates, the horizontal deflection plates which are placed vertically and the verticall deflection plates which are placed horizontally.

Spots of light are produced by tranferring the energy of the CRT beam to phosphour coating. When hit they are stopped and the kinetic energy is tranferrd to the phoshour. Part of the energy is converted into heat energy and the remaining is used to excite the eletrons to higher state. When they jump back to the ground state the absorbed energy is released in the form of light. The frequency or the colour of the light emmitted is proporional to energy difference between excited quantum and the ground state.

Persistance is defined as the time it takes by the emitted light from the screen to decay to one-tenth of its original intensity. Lower persistance phosphour requires higher refresh rates to maintain the picture on the screen and hence it is useful for the animation purposes. Higher persistance phosphour is used to the dislpay of highly complex static pictures.

The maximum number of points that can be displayed withtout overlap on a CRT screen is referred to as resolution or it can be defined as the number of points per centimetre that can be plotted vert' and horizontally. Aspect ratio is the ratio of vertical points to the horizontal points to produce equal length lines in both directions.

Raster Scan Displays

In the raster scan system the electron beam is swept one row at a time from top to bottom of the screen. As the electron beam moves across each row, the intensity is turned on and off to create a pattern of illuminated spots. Picture definition is stored in the memory area called the refresh buffer or frame buffer. The memory area holds the set of intensity values for all screen points. These stored values are then retrieved from the memory and then painted on the screen one row at a time. The row is called scan line and the screen points are called pixel (pictue element). On a black and white system with one bit per pixel, the frame buffer is called the bitmap and in the system with multiple bits per pixel it is called the pixmap. Raster scan displays usually have a refresh rate of 60-80Hz. The return to the left of the screen after refreshing each scan line, is called the horizontal retrace and the return to the top left corner of the screen at the end of every frame is called the vertical retrace. In some raster scan displays an inerlacing refreshing technique is used which is much more effective with lower refresh rate ones and helps in avoiding flickering.

Random Scan Displays

In the random scan displays, the electron beam is directed only to parts of the screen where a picture is to be drawn. Random scan displays draw the pictures one line at a time and hence they are called as vector displays or stroke writing or calligraphic displays. The component line can be drawn and refreshed by the random scan sytem in any specified order. The refresh rate depends on the number of lines to be drawn. Picture definition is stored as a set of line drawing commands in an area of memory referred to as the refresh display file, also called the display list, display program or refresh buffer. Random scan display systems are designed to draw all the component line 30 to 6 0 times per second.

Comparision of Raster and Random displays

random scan systems are designed for the line drawing applications and cannot display the realistic shaded scenes.

Vector displays have more resolution than the raster systems

Vector displays produce smooth line because the beam directly follows the line path where as in raster systems produce the jagged lines that are plotted as discrete point sets.