2. 2 Systems Architecture, Fifth Edition 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

3. 3 Systems Architecture, Fifth Edition Chapter Goals (continued) 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. 4 Systems Architecture, Fifth Edition

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

6. 6 Systems Architecture, Fifth Edition Matrix-Oriented Image Composition We’ll take a look at: –Display surfaces –Fonts –Color –Numeric pixel content

7. 7 Systems Architecture, Fifth Edition 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)

8. 8 Systems Architecture, Fifth Edition

9. 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. 10 Systems Architecture, Fifth Edition Color RGB (additive colors) –Generates color by mixing red, green, and blue CMY (subtractive colors) –Generates color using cyan (absence of red), magenta (absence of green), and yellow (absence of blue) CMYK color –Four-dye scheme using a separate black dye (K)

11. 11 Systems Architecture, Fifth Edition 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

12. 12 Systems Architecture, Fifth Edition 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)

13. 13 Systems Architecture, Fifth Edition 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 above compression methods are lossy, resulting in some loss of image quality

14. 14 Systems Architecture, Fifth Edition 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

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16. 16 Systems Architecture, Fifth Edition Adobe PostScript and Portable Document Format PostScriptPDF Used in printing and publishing and as graphic file interchange format and embedded printer technology Lacks features needed to generate and manage documents as an integrated whole Ability to distribute compressed documents with complete authorial control over exact format of the printed and displayed document, regardless of end user’s specific computer, OS, or printer

17. 17 Systems Architecture, Fifth Edition Video Display Character-oriented video display terminals (VDTs) Video controllers Video monitors

18. 18 Systems Architecture, Fifth Edition 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

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20. 20 Systems Architecture, Fifth Edition

21. 21 Systems Architecture, Fifth Edition 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

22. 22 Systems Architecture, Fifth Edition A video controller contains RAM, a microprocessor, and embedded software.

23. 23 Systems Architecture, Fifth Edition Video Monitors Separate from keyboards Common types –Cathode ray tubes (CRTs) –Liquid crystal displays (LCDs) –Plasma displays

24. 24 Systems Architecture, Fifth Edition 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

25. 25 Systems Architecture, Fifth Edition 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

26. 26 Systems Architecture, Fifth Edition How an LCD works

27. 27 Systems Architecture, Fifth Edition 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

28. 28 Systems Architecture, Fifth Edition Plasma displays have no backlight and no color filters; each pixel contains a gas that emits ultraviolet light when electricity is applied.

29. 29 Systems Architecture, Fifth Edition Printers Impact (dot matrix)Slow, noisy Relatively poor-quality output Inexpensive InkjetRelatively slow Excellent-quality output LaserRelatively fast Excellent-quality output

30. 30 Systems Architecture, Fifth Edition 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

31. 31 Systems Architecture, Fifth Edition An inkjet printer has disposable print cartridges that contain ink reservoirs, a matrix of ink nozzles, and electrical wiring and contact points.

32. 32 Systems Architecture, Fifth Edition 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

33. 33 Systems Architecture, Fifth Edition Laser printers operate with an electrical charge and the attraction of ink to that electrical charge.

34. 34 Systems Architecture, Fifth Edition 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

35. 35 Systems Architecture, Fifth Edition Manual Input Devices KeyboardsFor entering text and commands Pointing devicesFor pointing and selecting buttons or menu items For drawing For moving the position of cursor Input padsFor many of same functions as mice Also used for signature pads and touch screens

36. 36 Systems Architecture, Fifth Edition 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)

37. 37 Systems Architecture, Fifth Edition Pointing Devices Mouse Trackball Joystick Input pads (e.g., digitizer tablet) –Infrared detector –Photosensor –Pressure-sensitive pad

38. 38 Systems Architecture, Fifth Edition Optical Input Devices Detect light reflected off a printed surface or object into a photosensor Categories –Mark and pattern sensors –Image capture devices

39. 39 Systems Architecture, Fifth Edition 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

40. 40 Systems Architecture, Fifth Edition Advanced scanning technology can now read two-dimensional bar codes.

41. 41 Systems Architecture, Fifth Edition 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

42. 42 Systems Architecture, Fifth Edition Digital Cameras Employ optical scanning technology to capture single or still images and store them as raw compressed bitmaps

43. 43 Systems Architecture, Fifth Edition Portable Data Capture Devices Combine a keyboard, mark or bar-code scanner, and wireless communications to a wired base station or computer system Provide rapid data capture (e.g., warehouse inventory control, package routing and tracking)

44. 44 Systems Architecture, Fifth Edition Audio I/O Devices Sound: an analog waveform that can be sampled and stored as digital data Various mathematical transformations convert complex sounds to a single numeric representation Sampling and playback rely on analog-to-digital converters (ADC) and digital-to-analog converters (DAC) Monophonic versus polyphonic

45. 45 Systems Architecture, Fifth Edition Purposes of Sound Generation and Recognition General-purpose sound output (e.g., warnings) General-purpose sound input (e.g., digital recording for voice email messages) Voice command input Speech recognition Speech generation

46. 46 Systems Architecture, Fifth Edition Speech Recognition Conceptually simple, but complicated by speaker variability, phoneme transitions and combinations, and real-time processing Most current systems are speaker dependent Digital signal processor (DSP) –Specialized to process continuous streams of audio or graphical data –Commonly embedded in audio and video hardware

47. 47 Systems Architecture, Fifth Edition

48. 48 Systems Architecture, Fifth Edition Speech Generation Audio response unit –Generates spoken messages based on textual input (e.g., automated call routing) Speech synthesis –Stores individual phonemes within the system General-purpose audio hardware (sound card, multimedia controller)

49. 49 Systems Architecture, Fifth Edition General-Purpose Audio Hardware Typically packaged as an expansion card that connects to the system bus of a workstation Sound cards include an ADC, DAC, low-power amplifier, and connectors (jacks) for microphone, speaker, or headphone Musical Instrument Digital Interface (MIDI) –Compact storage format

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51. 51 Systems Architecture, Fifth Edition Summary Concepts, technology, and hardware used in communication between people and computers –Print and display concepts –Video display devices –Printers –Manual input devices –Optical input devices –Audio I/O devices