Unit 1

Chapter 1: Overview of Graphics systems Video Video Display Devices Raster-Scan System! Random-Scan Systems Inpt Devices Graphics Software

Introduction: Grap Graphi hics cs is the the famil amiliiar word ord for for all all. Grap Graphi hics cs means ans visu visual al repr epresen esenta tati tion on of thin things gs that that mean mean givi giving ng the the visu visual al repr epresen esenta tati tion on of  whatever you are thinking. Very simple example for graphics is: which you are using in your daily life; visuals in mobile phone and computer display. Why you have to study graphics as part of in your curriculum. Graphics is the part part of all all comp comput uter er soft softwa warre and and appl applic icat atio ions. ns. Witho ithout ut grap graphi hics cs,, no computer software and application. o graphics is important for computer science. !ne more thing computer is the one of the system for graphics so it"s must for computer science. #omput #omputer er graphi graphics cs involv involves es dis displa play, y, manipu manipulat lation ion and storag storage e of  pictur picture e and exper experim iment ental al data data for prope properr visual visuali$ i$ati ation on using using comput computer er..  %ypical  %ypical graphic system is consists of host computer with fast processor, large large memory, frame bu&er, input devices, output devices and interface devices.

'ramework of Graphics 'rom the above you can understand the concept and framework of graphics system system.. (n the above above )gure )gure left left sid side: e: applica applicatio tion n model model and applic applicati ation on progr program am are are belo belong ngs s to the the deve develo lope perr side side.. oft oftwa warre deve develo lope pers rs are are developing the programs and application. %hat programs and applications are are runnin running g in the graphics graphics systems. systems. #an get the output output in device devices s like like monito monitors rs and can give give the input to the system system using using input input device devices s like like keyboard.

!ne small example for the graphics system: calculator application in computer. computer. %hat calculator application is programed and developed by the software developer developer.. %hat calculator application is running in the computer graphics system and it is producing then the result based on the inputs.

Applications: *ot of applications is available for graphics systems. +ere ( listed some important areas. . G-( Graphical -ser (nterface/ 0asically it is an interface, between the user and graphic system. (t is help to interact the user and system vice versa by input and output. ome G-( components are: 1enus (cons #ursors croll bars 2ialog boxes Grids etc., 3. 4lotting in business 5. !6ce automation 7. 2esktop publishing 8. 4lotting in science and technology 9. dvertisements . #2. ?ntertainment @. imulation studies . 1ultimedia 3. 4rocess monitoring 5. 2igital (mage 4rocessing 7. ?ducation in training • • • • • •

Application packages and standards: Why need standards in graphics: tandards are very important for graphics because the programmers have to use common syntax, rules and procedures to build the graphics system. GKS o Graphics Aernel ystem by (!(nternational tandard !rgani$ation/ and B(merican Bational tandards (nstitute/ SRGP imple Caster Graphics 4ackage o PHIGS 4rogrammers +ierarchical (nteractive Graphics ystem o OpenGL !pen Graphic *ibrary o Output Primitives: 'our basic output primitives are available to draw any type of pictures.  %hose primitives are: 4!*D*(B? 'illed 4!*DG!B ?**(4?  %?E% • • • •

Major Area:

'our maFor areas of computer graphics are: 2isplay of (nformation 2esign and 1odeling imulation -ser (nterface !pes:  %wo %ypes available ctive Graphic ystem (n this type user can control the display with the help of G-( and (nput devices. ?xample: Video games 4assive Graphic ystem (n this type user can"t control the display. ?xample: %V #hannel • • • •

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"ideo #ispla! #evices: Video display devices are the most important output device in the graphics systems. %hree type of display devices available. %hese devices are working based on the #C% #athode Cay %ube/ only. %hese types are: 2irect View torage %ube 2V%/ #alligraphic or Candom can 2isplay system Cefresh and Caster can 2isplay system • • •

#irect "ie$ Storage u%e &#"S': (athode Cay %ube is the important part in the 2V% display. 'irst we will see some properties of 2V%. torage tube is #C% with a long persistence phosphor. (t provides the icker free display. Bo refreshing is necessary  slow moving electron beam draws a line on the screen creen has a storage mesh in which the phosphor is embedded (mage is stored as a distribution of charges on the inside surface of the screen • • • • • •

Operation o) electron gun $it* an accelerating anode:  %he below )gure illustrate the basic operation of a #C%.  beam of  electrons cathode rays/, emitted by an electron gun, passes through focusing and deection systems that direct the beam toward the speci)ed positions on the phosphor screen. %he phosphor then emits a small spot of  light at each position contacted by the electron beam. 0ecause the light emitted by the phosphor fades very rapidly. +lectron gun:  %he primary components of an electron gun in a #C% are the heated metal cathode and a control grid. +eat is supplied to the cathode by directing a current through a coil of wire, called the )lament, inside the cylindrical cathode structure. %his causes electrons to be Hkilled o&I the hot cathode surface. (n the vacuum inside the #C% envelope, the free, negatively charged electrons are then accelerated towards the phosphor coating by a high positive voltage. (ontrol Grid: (ntensity of the electron beam is controlled by setting the voltage level in the control grid which one )t over the cathode. pplying high negative voltage to the control grid will shut o& the beam from cathode by repelling

concept. o by adFusting the voltage level in the control grid you can change the brightness of the display. Accelerating Anode: ccelerating anode is used in #C% to accelerate the electron to strike the screen by high speed.

,ocusing Anode: 'ocusing anode is used in #C% to focus the electron beam in particular place in the screen. 'ocusing done by two ways in #C%: either using electric or magnetic )eld. ?lectrostatic focusing is commonly used in %elevision and computer monitors. %his is a positive voltage so it"s captured the electrons and point tuned the electron beam to hit the particular place in the screen. 'rom the above )gure: electron beams are hitting screen in the center point only. 0ut the screen si$e is sJuare so electron beam must to hit the all places in screen then only can see the picture in the screen. 2efection made in electron beam by two methods by ?lectrostatic deection 1agnetic deection • •

+lectrostatic de-ection: ?lectrostatic deection is done by the capacitive plates are )xed by hori$ontally and vertically to the screen. Vertical plates are used to move the beam vertically in the screen and hori$ontal plates are used to move the beam hori$ontally in the screen. Magnetic de-ection: 1agnetic deection coils helps to focus the electron beam all over the screen. #ra$%acks: 1odifying any part of image reJuires redrawing the entire image again #hange in the image reJuires to generate a new charge distribution in the 2V%

low process of drawing ?rasing takes about @.8 seconds Bo animation is possible with 2V%

(alligrap*ic or Random Scan #ispla!: (n this display system: #C% has the electron beam directed only to the parts of the screen where a picture is to be drawn. Candom scan monitors draw a picture one line at a time and for this reason are also referred to as vector displays or strokeKwriting or calligraphic displays/. #haracters also made of seJuence of strokes or short lines 0eam is deected from end point to end point !rder of the deection is dictated by arbitrary order of the display commands 4hosphor has short persistence decays in @K@@us  %he display must refresh with regular intervals minimum of 5@+$fps/ for icker free display Cefresh bu&er is available in this display system. (t is used to store the display list or display program to draw the picture  %he display processor interprets the commands in the refresh bu&er for plotting  %he display program has commands for point, line, and character plotting

(onceptual .lock diagram pplication programs are running in the host #4-. +ost #4- keeps the 2isplay programs and display commands in the display bu&er. 0ased on the program and command display controller will work and the picture processor sends the point coordinate values to the vector generator. Vector generator converts the digital coordinate value to analog voltage for beam deection circuit. 0eam deection circuit displaces the electron beam for drawing on the #C% screen.

 %he above )gure illustrates the operation of the electron beam deection in the random scan display. (n this display system: image is drawn

in the #C% screen by line. (n the )rst )g: its starting the image from one end point to another end point. 'inally using 5 lines, it is )nished the image of  triangle. !ne more example for drawing the image in #C% using random scan display:

Random Scan S!stem:  %he below )gure illustrates the random scan system: application program and graphic packages stored in the system memory. Graphic commands are translated to display )le in the system memory by package. 2isplay processor is accessing that display )le to refresh the screen.

Re)res* and Raster Scan #ispla! S!stem:  %he most common type of graphics monitor employing a #C% is the rasterKscan display, based on television technology. (n a rasterKscan system, the electron beam is swept across the screen, one row at a time from top to bottom. s the electron beam moves across each row, the beam intensity is turned on and o& to create a pattern of illuminated spots. 4icture de)nition is stored in a memory area called the refresh bu&er or frame bu&er. %his memory area holds the set of intensity values for all the screen points. tored intensity values are then retrieved from the refresh bu&er and IpaintedI on the screen one row scan line/ at a time. ?ach screen point is referred to as a pixel or pel shortened forms of picture element/.

#ra$ing Image:

'rom the above )gure: you can understand, how the raster scan system drawing image in the screen. (n this system, display screen is matrix of pixels. o each pixel properties coordination and intensity/ are controlled by video controller. ?ach pixel is addressable in frame bu&er ex: 8, 8/ here E and D coordination values are 8 and 8/. (n this system can"t draw the line directly. (t"s possible by point by point only so it is called point plotting. ee the )gure. (t"s drawing the line by point to point by scanning the screen from top to bottom row.

Arc*itecture o) simple raster/scan s!stem: (nteractive raster graphics systems typically employ several processing units. (n addition to the central processing unit or #4-, a specialKpurpose processor called the video controller or display controller is used to control the operation of the display device. !rgani$ation of a simple raster system is shown in below )gure.

Arc*itecture o) simple raster/scan s!stem (n the above )gure: frame bu&er is available in system memory and the video controller access the frame bu&er to refresh the screen.

Arc*itecture $it* 01ed portion o) s!stem memor! (n the above )gure: only one di&erence is: here frame bu&er area is )xed si$e in the system memory so this architecture is called )xed portion of  system memory. %he below )gure is two dimensional system. +ere the coordinates are E and D. these are used to )x the electron beam in the exact place in the screen. (n the frame bu&er two registers available, that is: register E and D. these registers are used to keep the E and D coordination: using these values video controller is drawing the image in the screen.

Input #evices: Various devices are available for data input on graphics systems. 1ost systems have a keyboard and one or more additional devices specially designed for interactive input. %hese include a mouse, trackball, space ball,  Foystick, digiti$ers, dials, and button boxes. ome other input devices used in particular applications are data gloves, touch panels, image scanners, and voice systems. +ere we will discuss some of the important devices.

Ke!%oard: n alphanumeric keyboard on a graphics system is used primarily as a device for entering text strings. %he keyboard is an e6cient device for inputting such nongraphic data as picture labels associated with a graphics display. Aeyboards can also be provided with features to facilitate entry of  screen coordinates, menu selections, or graphics functions. #ursorKcontrol keys and function keys are common features on general purpose keyboards. 'unction keys allow users to enter freJuently used operations in a single keystroke, and cursorKcontrol keys can be used to select displayed obFects or coordinate positions by positioning the screen cursor. Mouse:  mouse is small handKheld box used to position the screen cursor. Wheels or rollers on the bottom of the mouse can be used to record the amount and direction of movement. nother method for detecting mouse motion is with an optical sensor. 'or these systems: the mouse is moved over a special mouse pad that has a grid of hori$ontal and vertical lines. %he optical sensor detects movement across the lines in the grid. ince a mouse can be picked up and put down at another position without change in cursor movement, it is used for making relative change in the position of the screen cursor. !ne, two, or three buttons are usually included on the top of the mouse for signaling the execution of some operation.

rack%all and Space %all:  %rack ball is a ball that can be rotated with the )ngers or palm of the hand, to produce screenKcursor movement. 4otentiometers, attached to the ball, it measures the amount and direction of rotation. %rackballs are often mounted on keyboards. pace ball does not actually move. train gauges measure the amount of pressure applied to the space ball to provide input for spatial positioning and orientation as the ball is pushed or pulled in various directions. pace balls are used for threeKdimensional positioning and selection operations in virtual reality systems, modeling, animation, #2, and other applications.

 2o!sticks:  Foystick consists of a small, vertical lever called the stick/ mounted on a base that is used to steer the screen cursor around. 1ost Foysticks select screen positions with actual stick movement; others respond to the pressure on the stick. ome Foysticks are mounted on a keyboard. %he distance that the stick is moved in any direction from its center position corresponds to screenKcursor movement in that direction. 4otentiometers mounted at the base of the Foystick measure the amount of  movement, and springs return the stick to the center position when it is released. #ata Glove: 2ata glove is used to grasp a virtual obFect. %he glove is constructed with a series of sensors that detect hand and )nger motions. ?lectromagnetic coupling between transmitting antennas and receiving antennas is used to provide information about the position and orientation of  the hand. (nput from the glove can be used to position or manipulate obFects in a virtual scene. Image Scanners: 2rawings, graphs, color and blackKandKwhite photos, or text can be stored for computer processing with an image scanner by passing an optical scanning mechanism over the information to be stored. %he gradations of  gray scale or color are then recorded and stored in an array. !nce we have the internal representation of a picture, we can apply transformations to rotate, scale, or crop the picture to a particular screen area. We can also apply various image processing methods to modify the array representation of the picture. 'or scanned text input, various editing operations can be performed on the stored documents.