Chapter 7 Input/Output Technology

1. Chapter 7Input/Output Technology

2. Chapter 7Input/Output Technology Chapter Outline Basic Concepts of Print and Display Technology Focus – Adobe Postscript and Portable Document Format Video Display Printers Manual Input Devices Optical Input Devices Audio I/O Devices

3. Chapter Goals • Describe common concepts of text and image representation and display including digital representation of grayscale and color, bitmaps, and image compression techniques • Describe the characteristics and implementation technology of video display devices • List and describe the three predominant manual input technologies • Understand printer characteristics and technology • Describe various types of optical input devices including mark sensors, bar code readers, scanners, and digital cameras • Identify the characteristics of audio I/O devices, and explain how they operate

4. Chapter 7Input/Output Technology

5. Basic Print and Display Concepts • Share many features • Character representation methods • Measurement systems • Methods of generating color

6. Matrix-Oriented Image Composition • Display surfaces • Fonts • Color • Numeric pixel content

7. Display Surface • Commonly used: paper, cathode ray tubes, flat panel displays • Divided into rows and columns similar to a large matrix • Each cell (pixel) represents one simple component of an image • Resolution • Number of pixels displayed per linear measurement unit • Stated in dots per inch (dpi)

9. Fonts • Collection of characters of similar style and appearance • Usually measured in points (one seventy-second of an inch), which refers to height of characters

10. Color • RGB (additive colors) • Properly called “color” • Generates color by mixing red, green, and blue • CMY (subtractive colors) • Properly called “pigment” • Generates color using • cyan (absence of red) • magenta (absence of green) • yellow (absence of blue) • CMYK color • Four-dye scheme using a separate black dye (K)

11. Colors by Electromagnetic Wavelength and Frequency

12. Color CodingRGBOne byte for each basic color

13. Numeric Pixel Content • Bitmap • Stored set of numeric pixel descriptions • Monochrome display • Displays one of two colors • Requires only one bit per pixel • Grayscale display • Displays black, white, and shades of gray

14. Numeric Pixel Content • Palette • A table of colors • Number of bits used to represent each pixel determines table size • Dithering • Generates color approximations by placing small dots of different colors in an interlocking pattern • Half-toning (grayscale dithering)

15. Image Storage Requirements • Depends on number of bits that represent each pixel and on image height and width in pixels • Can be reduced with bitmap compression • Graphics Interchange Format (GIF) • Joint Photographic Experts Group (JPEG) • Moving Pictures Experts Group (MPEG) • All compression methods are lossy, resulting in some loss of image quality

16. Image Description Languages (IDL) • Address drawbacks of bitmaps (large size and device dependence) by storing images compactly • Can represent image components in several ways • Embedded fonts • Vectors, curves, and shapes • Embedded bitmaps

17. Vector Display

18. Adobe PostScript and Portable Document Format

19. Adobe PostScript

20. Video Display • Character-oriented video display terminals (VDTs) • Video controllers • Video monitors

21. Character-Oriented VDTs • Integrated keyboard and video display surface • VDTs • Most common form of video display in 1970s and much of 1980s (until PCs) • Network computers or thin clients • New class of VDT in 1990s • Limited processing capabilities

22. Video Display

23. Wyse TechnologyVDTs and Thin Clients

24. Video Controller • Enables communication between computer system and monitor • Accepts commands and data transmitted via a bus from the CPU • Generates TV-style analog video signal, which is transmitted to the monitor • Refresh cycle and refresh rate; video RAM; dual porting; graphics accelerators

25. Video Controller Contains RAM, a microprocessor, and embedded software.

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

27. CRT • Enclosed vacuum tube; electron beam is focused toward front surface of the tube, which is coated in phosphor • Technology relatively old; has disadvantages • Physical size and weight • Power consumption

28. LCD • Contains matrix of liquid crystals sandwiched between two polarizing filter panels • Active and passive matrix displays • Manufactured with thin film transistor (TFT) technology • Compared with CRTs • Less contrast • Reduced size, weight, and power consumption • Higher cost

29. How an LCD works

30. 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, less than CRTs • Shortcomings • Limited operational lifetime • Larger pixel size reduces comparative image quality when viewed from short distances

31. Plasma Displays Plasma displays have no backlight and no color filters; each pixel contains a gas that emits ultraviolet light when electricity is applied.

32. Printers

33. Printer Communication • Impact printers • ASCII or Unicode characters • Inkjet and laser printers • Use pixels as fundamental output unit • Have relatively large buffers • IDLs are commonly used to improve printer performance

34. Dot Matrix Printers

35. Daisy Wheel Printers

36. Inkjet Printers • Most common printing technology • Prints with liquid ink placed directly onto paper • Uses mechanical movement or heat to force ink out of nozzle • Paper is drawn past moving print head • Resolution is up to 600 dpi

37. Inkjet Printers An inkjet printer has disposable print cartridges that contain ink reservoirs, a matrix of ink nozzles, and electrical wiring and contact points.

38. Lasar Printers

39. Lasar Printers Laser printers operate with an electrical charge and the attraction of ink to that electrical charge.

40. Lasar Printers

41. Lasar Printers

42. Lasar Printers

43. Plotters • Printers that generate line drawings on wide sheets or rolls of paper • Use inkjet technology • Ideal for blueprints and other engineering drawings • Also called large format printers

44. Manual Input Devices

45. Keyboards • Translate keystrokes directly into electrical signals • Generate bit stream outputs (scan code) with a keyboard controller • Can connect to computer in various ways(e.g., PS/2, USB, wireless)

46. Pointing Devices • Mouse • Trackball • Joystick • Input pads (e.g., digitizer tablet) • Infrared detector • Photosensor • Pressure-sensitive pad

47. Optical Input Devices • Detect light reflected off a printed surface or object into a photosensor • Categories • Mark and pattern sensors • Image capture devices

48. Mark Sensors and Bar-Code Scanners • Mark sensor • Scans for light or dark marks at specific locations on a page (e.g., standardized multiple-choice test) • Bar code scanner • Detects specific patterns of vertical bars of varying thickness and spacing • Typically used to track large numbers of inventory items

49. PDF417 Bar Code Advanced scanning technology can now read two-dimensional bar codes.

50. Optical Scanners • Generate bitmap representations of printed images • Bright white light shines on the page; reflected light is detected by an array of photosensors • Optical character recognition (OCR) devices • Combine optical scanning technology with intelligent interpretation of bitmap content