Overview of Graphics System


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Lecture presentation for BCA students.Latest Syllabus.

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Overview of Graphics System

  1. 1. Objectives At the end of this chapter the reader will be able to: • Describe and distinguish raster and random scan displays • Describe various display devices. • Describe how color CRT works..
  2. 2. Structure 1. 2. 3. 4. 5. 6. 7. 8. 9. Introduction Refresh CRT Random-Scan and Raster Scan Displays Random–Scan and Raster Scan System Graphics Monitor and Workstation Input Devices Hard Copy Devices Graphics Software Summary
  3. 3. The Primary Output Device of the Graphic System ?? How does this Operate???
  4. 4. Video Monitor Back
  5. 5. Basic Design of Magnetic deflection CRT
  6. 6. Basic Design of Magnetic deflection CRT
  7. 7. oIntensity Distribution oResolution oAspect Ratio oPersistence
  8. 8. The intensity is greatest at the center of the spot, and decrease with Gaussian distribution out to the edges of the spot.
  9. 9. The maximum number of points displayed without overlap on a CRT is referred to as the resolution. A more precise definition of resolution is the number of points per centimeter that can be plotted horizontally and vertically, although it is often simply stated as the total number of points in each direction. This depends on the type of phosphor used and the focusing and deflection system & the intensity to be displayed.
  10. 10. Overlap
  11. 11. Another property of video monitors . This number gives the ratio of vertical points to horizontal points necessary to produce equal-length lines in both directions on the screen. An aspect ratio of 3/4 means that a vertical line plotted with three points has the same length as a horizontal line plotted with four points.
  12. 12. Persistence is defined as the time it takes the emitted light from screen to decay to one-tenth of its original intensity.
  13. 13. These monitors displays color pictures by using combination of phosphors that emit different colored light. There are two techniques for producing color displays on CRT. They are : 1. Beam Penetration Method 2. Shadow Mask Method
  14. 14. Similar to simple CRT but contains different colored Phosphor layers(Red and Green) coated onto inside of the screen. The displayed color depends on how far the electron beam penetrates into the layers. The speed of electrons – beam acceleration voltage. Slow Electrons  Red color Fast Electrons  Green color Intermediate Speed Electrons  Yellow and orange colors Quality of Picture is not so good and is inexpensive.
  15. 15. Works on the principle of combining the basic colors - Red, green and Blue - in suitable proportions to get a combination of colors. Uses 3 electron gun placed one by the side of the other to form a triangle or a "Delta". Each pixel point on the screen is also made up of 3 types of phosphors to produce red, blue and green colors. Before the phosphor screen is a metal screen, called a "shadow mask". This plate has holes placed strategically, so that the beams from the three electron guns are focused on a particular pixel.
  16. 16. When the beam passes through the mask they form a dot triangle. Another configuration is inline arrangement of electron guns and RGB dots on screen are aligned on one scan line. By varying intensity , we get different colors (White,Grey,Yellow,Cyan)
  17. 17. Beam Penetration method Where Used Colors Color Dependency Shadow Mask method It is used with Random Scan System to display color. It is Used With Raster Scan System to display color. It can displays Only four colors i.e. Red it can display Millions of colors. , Green, Orange and Yellow. Less colors are available because the Millions of colors are available because colors in Beam Penetration depends the colors in Shadow Mask depends on the speed of the electron beam. on the type of the ray. Cost It is Less Expensive as compared to Shadow Mask. It is More Expensive than other methods. Picture Quality Quality of picture is not so good i.e. Poor with Beam Penetration Method. Shadow Mask gives realism in picture with shadow effect and millions of color. It gives Low Resolution. It gives High Resolution. Resolution Criteria In Beam Penetration method, Color In Shadow Mask Method, there are no display depends on how far electron such criteria for producing colors. It is excites outer Red layer and then Green used in computers, in color TV etc. layer.
  18. 18. An alternative method for maintaining a screen image is to store the picture information inside the CRT instead of refreshing the screen. A direct-view storage tube (DVST) stores the picture information as a charge distribution just behind the phosphor-coated screen. Two electron guns are used in a DVST. One, the primary gun, is used to store the picture pattern; the second, the flood gun, maintains the picture display . A DVST monitor has both disadvantages and advantages compared to the refresh CRT. Because no refreshing is needed, very complex pictures can be displayed at very high resolutions without flicker. Disadvantages of DVST systems are that they ordinarily do not display color and that selected parts of a picture cannot be erased. To eliminate a picture section, the entire screen must be erased and the modified picture redrawn. The erasing and redrawing process can take several, seconds for a complex picture. For these reasons, storage displays have been largely replaced by raster systems.
  19. 19. Most common method Beam is swept across the screen one line at a time, pixel by pixel Uses Frame Buffer (an array ,on and off state) Screen is refreshed 60 times/sec –Interlacing (Odd numbered and Even numbered lines) Progressive Scanning – alternate to interlacing,reduces Flickers- refreshes every line on screen
  20. 20. Also called Vector/Stroke/Calligraphic Displays Beam is swept across the screen one line at a time, only intended point Picture Definition – Display file (set of line drawing commands) Only area where picture is drawn is refreshed
  21. 21.  It has Poor or Less Resolution  It has High Resolution Electron beam is directed from top to bottom at a time on screen , but electron beam is directed to whole screen. Electron beam is directed only to that part of screen is required to be drawn. It is less expensive It is expensive Refresh Rate is 60 to 80 frames / second Refresh Rate depends on no.of lines to be displayed ,30 to 60 times/ second Stores Picture Definition in Frame Buffer Stores Picture Definition in Display files Zig Zag line is produced Smooth line is produced
  22. 22. Interactive raster-graphics systems typically employ several processing units : CPU Special purpose register – Video/Display Controller System Memory
  23. 23. CPU System Memory System Bus I/O Devices Video Controller Monitor
  24. 24. It consists of the three components : (1) Frame Buffer (2) Monitor like a TV set without the tuning and receiving electronics. (3) Display Controller It passes the contents of the frame buffer to the monitor.
  25. 25. CPU System Memory Frame Buffer System Bus I/O Devices Video Controller Memory
  26. 26. Raster Scan Generator X Register Y Register Memory Address Frame Buffer Pixel Register Intensity
  27. 27. Display Processor Memory CPU Frame buffer Display Processor System Bus I/O Devices Video Controller System Memory Monitor
  28. 28. CPU System Memory Display Processor Monitor System Bus I/O Devices Application programs are stored in system memory. Graphics commands in the program are translated by the graphics package into a display file stored in the system memory. This display file is accessed by the display processor to refresh the screen. Display processor in a random scan system is referred to as a display processing unit or graphics controller.
  29. 29. 9066
  30. 30. Work station : a desktop computer terminal, typically networked and more powerful than a personal computer.
  31. 31. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Keyboard Mouse Trackball & Spaceball Joystick Data Glove Digitizers Image Scanners Touch Panels Light Pens Voice Systems
  32. 32. A device for enter text strings.
  33. 33. Hand held device used to position the cursor.
  34. 34. It is a ball that is a ball that can be rotated with fingers to produce cursor movements. Potentiometers attached to the ball , measure the amount and direction of rotation. Normally mounted on KB. 2d positioning device.
  35. 35. Spaceball six-degree-of-freedom input devices. The Spaceball may be used to rotate, translate, and scale molecules, using up to 6 control axes simultaneously. The Spaceball can be used simultaneously with the mouse. independently and Spaceball are used for 3D positioning and selection operations in virtual reality systems, modeling, animation, CAD, and other application.
  36. 36. A joystick is a input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. Used to select screen positions with actual stick movement, others respond to pressure on the stick.
  37. 37. A glove equipped with sensors that sense the movements of the hand and interfaces those movements with a computer. Data gloves are commonly used in virtual reality environments where the user sees an image of the data glove and can manipulate the movements of the virtual environment using the glove.
  38. 38. A device for drawing , painting , or interactively selecting co-ordinate positions on an object. Conversion of a typically analog object, image or a signal into digital form.
  39. 39. It is a type of Digitizer. It enables a user to hand-draw images, animations and graphics, similar to the way a person draws images with a pencil and paper. These tablets may also be used to capture data or handwritten signatures. It can also be used to trace an image from a piece of paper which is taped or otherwise secured to the surface. Capturing data in this way, either by tracing or entering the corners of linear poly-lines or shapes is called digitizing.
  40. 40. Is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image.      Types : Drum FlatBed Film Hand Held Smart phone Scanner
  41. 41. Touch panels allow displayed objects or screen position s to be selected with touch of a finger. Types of Touch Panels : a. Resistive Film Touch Panels b. Capacitive Touch panels c. Surface Capacitive Touch Panels d. Surface Acoustic Wave Touch Panels e. Optical Touch Panels f. Electromagnetic Induction Touch Panels
  42. 42. It is in the form of a light-sensitive wand used in conjunction with a computer's CRT display. It allows the user to point to displayed objects, or draw on the screen, in a similar way to a touch screen but with greater positional accuracy. A light pen can work with any CRTbased display, but not with LCD screens, projectors and other display devices.
  43. 43. A device in which speech is used to input data or system commands directly into a system. Such equipment involves the use of speech recognition processes, and can replace or supplement other input devices. Some voice input devices can recognize spoken words from a predefined vocabulary, some have to be trained for a particular speaker.
  44. 44. The quality of the picture obtained from the device depends on dot size and no of dots/inch.
  45. 45. Classification : a) General Programming Package Provides functions that can be used in HLP Lang. For Programmers. Eg : Graphics Library b)Special Purpose Application Package Provides functions for graphic Design For Non Programmers Eg : CAD
  46. 46. 5 Coordinate Representations in Graphics : General graphics packages are designed to be used with Cartesian coordinate representations (x,y,z). Usually several different Cartesian reference frames are used to construct and display a scene: Modeling coordinates are used to construct individual object shapes. World coordinates are computed for specifying the placement of individual objects in appropriate positions.
  47. 47. Normalized coordinates are converted from world coordinates, such that x,y values are ranged from 0 to 1. Device coordinates are the final locations on the output devices. (xmc,ymc)  (xwc,ywc)  (xnc,ync) (xdc,ydc)
  48. 48. The basic building blocks for pictures are referred to as Output Primitives. They include character strings, geometric entities. Attributes are properties of O/P primitives. It describes how a primitive should be displayed. Geometric transformation is changing the size ,position, orientation of an object within a scene. Viewing transformations are used to specify the view that is to be presented & the portion of the o/p display area that is to be used.
  49. 49. Pictures can be sub divided into small parts called Structures or segments or objects. Each structure defines one logical unit of the picture. I/P functions are used to control and process the data flow from these interactive devices. Control operation is responsible for house keeping tasks.
  50. 50. The primary goal of standardized graphics software is portability. First Graphic S/W standard : Graphical Kernel System (GKS) Second Graphic S/W standard : Programmers Hierarchical Interactive Graphics Standard (PHIGS) Third Graphic S/W standard : PHIGS+ These standards were adopted by ISO and ANSI. Fourth Graphic S/W standard : Computer Graphics Interface (CGI) Fifth Graphic S/W standard : Computer Graphic Metafile (CGM )
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