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Chapter 7 Input / Output Technology

Chapter 7 Input / Output Technology

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Chapter 7 Input / Output Technology

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  1. Chapter 7Input / Output Technology

  2. Chapter Goals • Describe manual input devices and how they are implemented. • Describe concepts of text and image representation and display, including digital representation of grayscale and color, bitmaps, and image description languages. • Explain the characteristics and implementation technology of video display devices. • Understand printer characteristics and technology. • Identify the characteristics of audio I/O devices, and explain how they operate. INFO 225: Chapter 7

  3. Chapter Topics • Describes the concepts, technology and hardware used in communication between people and computers. • Understand the importance of I/O technology. INFO 225: Chapter 7

  4. Manual Input Devices • Keyboard Input • Pointing Devices INFO 225: Chapter 7

  5. Manual Input Devices Keyboard Input • Keyboard devices translatekeystrokes directly into electrical signals. • A keyboard controller is used to generate bit stream outputs according to an internal program or lookup table. • A keyboard controller generates an output called a scan code. • A scan code is a one or two-byte data element that represents a specific keyboard element. INFO 225: Chapter 7

  6. Manual Input Devices Pointing Devices Translates the spatial position of a pointer, stylus, or other selection device into numeric values within a system of two-dimensional coordinates. • Mouse • Trackball • Joystick • Digitizer Tablet INFO 225: Chapter 7

  7. Manual Input Devices Mouse – a pointing device that is moved on a flat surface such as a table, desk or rubber pad. Trackball – a mouse with the roller ball on the top. The roller ball is moved by the fingertips, thumb or palm of the hand. Joystick – used as an input device with computer games. Digitizer Tablet – uses a pen, or stylus, and a digitizing tablet. The tablet is sensitive to the placement of the stylus at any point on its surface. INFO 225: Chapter 7

  8. Basic Concepts of Print and Display • Sharing features of printing & videotechnologies • Character representation methods • Measurement systems • Methods of generating color • Matrix-Oriented Image Composition • Fonts • Color • Pixel Content • Image Storage Requirements • Image Description Languages INFO 225: Chapter 7

  9. Basic Concepts of Print and Display Matrix-Oriented Image Composition • Display surfaces commonly are LCD, Flat Panel, Cathode ray tubes (CRT), or Paper • Display surfaces can be divided into rows and columns similar to a large table or matrix. • Each cell in the table represents one component of the image. INFO 225: Chapter 7

  10. Basic Concepts of Print and Display Matrix-Oriented Image Composition • One of the cells is a pixel (Short for Picture Element). • Number of pixels in display area =F(display area size–HxW, pixel size) Eg: • Find Number of pixel in a 19” flat panel display. • Pixel size:0.25mm2 • Display size: 11”(28cm)x14.5”(37cm)” • Therefore No. of pixels: 28x(10)x37x(10)/0.25 = 414,400 • For 0.24mm2 • 28x(10)x37x(10)/0.24 = 431,666 INFO 225: Chapter 7

  11. Basic Concepts of Print and Display • The resolution of the display is: The number of pixels displayed per linear measurement unit. • Example: 40 pixel/cm or = 100 pixel/in Resolutionis stated in: dots per inch(dpi). (Dot is equivalent to a pixel) INFO 225: Chapter 7

  12. Basic Concepts of Print and Display • Higher resolution correspond to smaller pixel size which makes better quality because smoother curves incorporate into the image • Higher resolution = smaller pixel size = higher quality of print or display Two resolutions displaying the same text Top: 50 dpi and bottom: 200 dpi INFO 225: Chapter 7

  13. Basic Concepts of Print and Display Matrix-Oriented Image Composition • dpi is used to indicate resolution for printers and monitors. But is more popular in US and specially for printers. • Printer resolutions are between 125 to 600 dpi • 125 dpi is for a low quality dot matrix printer • 600 is for a laser or ink-jet printer • Typesetting equipment have a resolution of 1000-2000 dpi. INFO 225: Chapter 7

  14. Basic Concepts of Print and Display Matrix-Oriented Image Composition • Image size is stated (measured) in pixel: HeightxWidthor RowxColumn Or: 300x200 • The image size depends on pixel size • If pixel size is 0.3 mm the above image size is 90mmx60mm • If pixel size is 0.25 mm the size of the above image is 75mmx50mm INFO 225: Chapter 7

  15. Basic Concepts of Print and Display Matrix-Oriented Image Composition • Point = (1/72) inch is adapted as the standard pixel size for printers. • This measure is used today in spite the fact that printers can apply ink pixels smaller that (1/1000) of an inch. INFO 225: Chapter 7

  16. Basic Concepts of Print and Display Matrix-Oriented Image Composition • Dot pitch: is a measure of monitors and printers resolution. Dot pitch is the vertical distance between pixels in (mm). • In monitors, it is a measure of image clarity. • A smaller dot pitch generally means a crisper and sharper image • This measure is more popular for monitors. • High quality monitors have dot pitch of less than 0.28mm • Current range of dot pitch is 0.24mm – 0.28 mm INFO 225: Chapter 7

  17. Basic Concepts of Print and Display INFO 225: Chapter 7

  18. Basic Concepts of Print and Display • Font – a collection of characters of similar style and appearance. INFO 225: Chapter 7

  19. Basic Concepts of Print and Display • Common unit for measuring font size is points. INFO 225: Chapter 7

  20. Basic Concepts of Print and Display • The measure of point refers to the height of the characters but not their width. The width is scaled to match the height. • Characters vary in height and placement. E.g. T is taller than a, and P & Q extend below the text baseline. • A font size is the distance between the top of the highest and bottom of lowest character in the font (e.g. T & p or q). INFO 225: Chapter 7

  21. Basic Concepts of Print and Display Color: The human eye interprets different light frequencies as different colors. INFO 225: Chapter 7

  22. Basic Concepts of Print and Display Color for video • For video displays, color is generated directly by the display device. • The video display industry has used red, green, and blue as primary colors (RBG). • A video display that generates color uses mixtures of these colors. • Video display colors are called additive colors. INFO 225: Chapter 7

  23. Basic Concepts of Print and Display Color for print • For print, color is light frequency reflected from the paper. • The printing industry generates color using the inverse of the primary video display colors. • Printing colors are called subtractive color (CMY). • Subtracting colors are cyan (absence of red), magenta (absence of green), and yellow (absence of blue). INFO 225: Chapter 7

  24. Basic Concepts of Print and Display Pixel Content • Pixel content must be described digitally in bits. • The number of bits required to describe a pixel depends on color (monochrome, grayscale, or color). • A stored set of digital numbers describing a pixel is called a bit map. INFO 225: Chapter 7

  25. Basic Concepts of Print and Display Pixel Content • Monochrome use 1 bit. 0=back, 1=white • Grayscale using 3 bits produce 8 shades of gray (23=8). • Grayscale using 8 bits produce 256 shade of gray (28=256)including pure black and pure white. INFO 225: Chapter 7

  26. Basic Concepts of Print and Display Pixel Content • Chromatic depth or resolution: Refers to the number of distinct colors or gray shades that can be displayed. INFO 225: Chapter 7

  27. Basic Concepts of Print and Display Pixel Content • For color display, three separate set of bits are required to represent different intensity of additive (RGB) or subtractive (CMY). • Example: Color display using 24 bits uses 8 bits to represent intensity of each color (0-255) in additive or subtractive color scheme. • 255:0:0  bright red • 255:255:0  light magenta • 127:63:0  Brown • The number of distinct colors (chromatic depth) is 2(3x8) = 16 million Color display with less than 24 bits cause each primary color be represented by less than 8 bits, causing a problem as computers deal with Byte size data more efficiently. INFO 225: Chapter 7

  28. Basic Concepts of Print and Display Pixel Content • Alternatively palette is use to display colors • A palette is a table of colors. • A palette of 8 bits can display 28=256 colors. • A palette of 4 bits can display 24 =16 colors. • In this case the intensity of each primary color will be FIXED. E.g. 127:255:127  light green INFO 225: Chapter 7

  29. Basic Concepts of Print and Display INFO 225: Chapter 7

  30. Basic Concepts of Print and Display Pixel Content • Color can also be produced using dithering. • Dithering places small dots of different colors in an interlocking pattern. Human eye interpret this as uniform color representing a mixture of the dot colors. • 50% red + 50% blue  interpreted as magenta • 50% black + 50% white  interpreted as gray • Dithering is used in devices not capable of applying fine differences in color. • e.g. an ink-jet that only produces 4 different amounts of a single dye in one pixel area, produce 43=64 colors. Using dithering can simulate several shades between each of 4 colors. INFO 225: Chapter 7

  31. Basic Concepts of Print and Display Dithering: A technique used in computer graphics to create the illusion of varying shades of gray on a monochrome display or printer, or additional colors on a color display or printer. Dithering relies on treating areas of an image as groups of dots that are colored in different patterns. Akin to the print images called halftones, dithering takes advantage of the eye's tendency to blur spots of different colors by averaging their effects and merging them into a single perceived shade or color. Depending on the ratio of black dots to white dots within a given area, the overall effect is of a particular shade of gray. Dithering is used to add realism to computer graphics and to soften jagged edges in curves and diagonal lines at low resolutions INFO 225: Chapter 7

  32. Basic Concepts of Print and Display Image Storage Requirements • Image storage requirements apply to images stored in primary and secondary storage, and to buffers used in I/O devices. • Image storage requirements can be reduced with image compression techniques. INFO 225: Chapter 7

  33. Basic Concepts of Print and Display Image Storage Requirements Compression Techniques: • Graphics Interchange Format (GIF) • Joint Photographic Experts Group (JPEG) • Moving Pictures Experts Group (MPEG) INFO 225: Chapter 7

  34. Basic Concepts of Print and Display Image Description Languages • Use a symbolic language to describe primitive image components. • Can use a vector list. • Describe the image components that are straight-line segments or can be built from segments. INFO 225: Chapter 7

  35. Basic Concepts of Print and Display INFO 225: Chapter 7

  36. Technology Focus - Postscript INFO 225: Chapter 7

  37. Technology Focus - Postscript x= 245 y= 365 x= 340 y= 365 x= 245 y= 265 x= 340 y= 265 INFO 225: Chapter 7

  38. Video Display • Character-Oriented Video Display Terminals • Graphic Video Display Devices • CRTs • Flat Panel Displays INFO 225: Chapter 7

  39. Video Displays Character-Oriented Video Display Terminals • Commonly used during 1970s and 1980s. • Terminal – consists of an integrated keyboard and television screen. • Used primarily today in systems such as retail checkout counters and factory floor environments. INFO 225: Chapter 7

  40. Video Display Functional components of a video display terminal (VDT) The display driver contained relatively simple electronic circuitry that translated ASCII/EBCDIC into a corresponding pixel matrix then passed to the display generator. In modern VDTs, the display driver is an embedded computer with its μp, RAM & ROM. Communication controller has changed from a slow serial port to USB, IEEE Firewire, or Ethernet. Network computer or thin client was a hybrid device with a mix of VDT and microcomputer developed by Wyse Technology in 1990s INFO 225: Chapter 7

  41. Video Display Graphic Video Display Devices • Used for displaying diagrams such as construction blueprints, wireframe models, writing diagrams and to produce mathematical graphs. • By the mid-1980s, monitors were manufactured. • Monitors operate as independent devices under control of a video controller attached to the system bus. INFO 225: Chapter 7

  42. Transfer of video data from the primary storage to the monitor. Video Display A modern video display (monitor) is connected to a video controller which is attached to the system bus. The video controller accepts commands and data transmitted via a bus from the CPU and generates a TV-style analog video signal which is transmitted continuously to the monitor. Video controller with monitor and bus connections Similar to Cache but has differences, Video RAM, VRAM INFO 225: Chapter 7

  43. Video Display Video Controllers • Enables communication between computer system and monitor • Accepts commands and data transmitted via a bus from the CPU • Generates analog or digital video signals, which are transmitted to the monitor • Terms: • Refresh cycle and refresh rate; video RAM; dual porting; graphics accelerators

  44. Video Display CRT • Current monitors are implemented using cathode ray tubes (CRT). • A CRT is an enclosed tube. • An electron gun in the rear of the tube generates a stream of electrons. • Pixel illumination is controlled by pulsing the electron beam. • The number of times per second that the entire surface is scanned by the electron gun is called the refresh rate. INFO 225: Chapter 7

  45. Video Display Flat Panel Display • Liquid Crystal Display – is a flat panel matrix that consists of encapsulated liquid crystals sandwiched between two polarizing panels. • Active Matrix Display – Uses one or more transistors for every pixel. • Passive Matrix Display – shares transistors among rows and columns of pixels. • Electroluminescent Displays – similar to construction of LCDs. Color is generated with three matrices of different colored phosphors. INFO 225: Chapter 7

  46. Video Monitors • Separate from keyboards • Common types • Cathode ray tubes (CRTs) • Flat panel displays • Liquid crystal displays (LCDs) • Plasma displays • LED displays

  47. LCD • Contains matrix of liquid crystals sandwiched between two polarizing filter panels • Active and passive matrix displays • Manufactured with thin film transistor (TFT) technology

  48. FIGURE 7.9 Light entering the rear filter can’t pass through the front filter if the liquid crystal is electrically charged (top); removing the charge returns the liquid crystal to its twisted state, allowing light to pass (bottom) Courtesy of Course Technology/Cengage Learning

  49. Plasma Displays • Combine elements of CRT and LCD technology • Flat panel, active matrix devices • Actively generate colored light near surface of the display • Good brightness and viewing • Require more power than LCDs

  50. FIGURE 7.10 A plasma display pixel Courtesy of Course Technology/Cengage Learning