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Theoretical Foundations of Multimedia Chapter 3 Hardware that Enables Multimedia n Input and Output Devices n Virtual Reality Devices n Modems and Network.

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Presentation on theme: "Theoretical Foundations of Multimedia Chapter 3 Hardware that Enables Multimedia n Input and Output Devices n Virtual Reality Devices n Modems and Network."— Presentation transcript:

1 Theoretical Foundations of Multimedia Chapter 3 Hardware that Enables Multimedia n Input and Output Devices n Virtual Reality Devices n Modems and Network Interfaces

2 Theoretical Foundations of Multimedia Chapter 3 Input and Output Devices n Monitors n Speakers and MIDI interfaces n VR helmets and immersive displays n Keyboards and OCR devices n Digital cameras, scanners, & CD-ROMs n MIDI keyboards and microphones n Video cameras and frame grabbers n Mice, track balls, joysticks, and VR gloves and wands Output Input

3 Theoretical Foundations of Multimedia Chapter 3 Monitors A simplified cathode ray tube (CRT)

4 Theoretical Foundations of Multimedia Chapter 3 Monitors n Pixel — a picture element; a dot of color on the screen n Three different phosphors at each pixel to create the color RGB ( Red, green, blue) RGB ( Red, green, blue) n CYM (Cyan, yellow, magenta)

5 Theoretical Foundations of Multimedia Chapter 3 Monitors Raster Scanning

6 Theoretical Foundations of Multimedia Chapter 3 Monitors n Refresh rate — the frequency at which the phosphors are excited n Normally the refresh rate is givenin Hertz For flicker-free images 75 Hz or faster is desirable For flicker-free images 75 Hz or faster is desirable n The refresh rate for a projector needs to be coordinated with the monitor

7 Theoretical Foundations of Multimedia Chapter 3 Monitors n The digitized image to be displayed must be stored in a buffer n The stored image is said to be “bit-mapped,” because, for monochrome images, the map used just one bit per pixel n Multimedia monitors use 24 bits per pixel (8 for each color); can define >16 million colors

8 Theoretical Foundations of Multimedia Chapter 3 A Good Multimedia Monitor n Large enough for comfortable viewing, probably 15” or greater n Pixel size of no more than 0.28mm n Refresh rate of at least 75 Hz n Capable of displaying 24-bit color n Designed for the CPU and operating system n Ergonomically comfortable and attractive

9 Theoretical Foundations of Multimedia Chapter 3 Speakers and MIDI Interfaces n Storage of digitized sound files n Reproduction via digital-to-analog conversion sent to a loudspeaker n Built-in speakers often do not havesufficient fidelity n Low-powered (3- to 5-watt) externalspeakers or head-phones will serve a single user and provide excellent fidelity

10 Theoretical Foundations of Multimedia Chapter 3 n Storage of synthesizer command files n Create the sounds by sending the commands to a synthesizer n Musical Instrument Digital Interface(MIDI) standard (1982) n MIDI includes both a hardware and a message standard Speakers and MIDI Interfaces

11 Theoretical Foundations of Multimedia Chapter 3 Speakers and MIDI Interfaces n MIDI hardware standard defines cables, connectors, circuits, andelectrical signals n MIDI message standard defines a u Device number for multiple device systems u Control segment that gives an instrument-specific command u Data segment containing the information needed by that instrument for that command

12 Theoretical Foundations of Multimedia Chapter 3 Alphanumeric Keyboards n For entering commands, text, and data n Each key is a switch that closes when it is depressed, sending a code to the CPU n The arrangement of the keys may vary n The most common is QWERTY n Another arrangement is Dvorak

13 Theoretical Foundations of Multimedia Chapter 3 Choosing a Keyboard n Does it include all of the needed characters, including command keys? n Is it ergonomically comfortable and safe, preventing repetitive stress syndrome?

14 Theoretical Foundations of Multimedia Chapter 3 Optical Character Recognition (OCR) n Hardware — scans the text image n Software — systematically checks the entire image for patterns of light and dark that it recognizes as alphabetic, numeric, or punc- tuation characters n OCR software entails pattern recognition, a sophisticated logic problem

15 Theoretical Foundations of Multimedia Chapter 3 E e E E e e E E e E e e E E E e e E e e It is relatively easy for a human to recognize each of these characters as the letter “e.” For the pattern recognition logic in OCR software, this is very difficult. Optical Character Recognition (OCR)

16 Theoretical Foundations of Multimedia Chapter 3 Digital Cameras and Scanners n Real Image — n Real Image — a portion of what is physically present in nature Digital Image — n Digital Image — a representation of a real image in which individual points are encoded to represent the wavelength and intensity of light at that point Still Image — n Still Image — a single snapshot of an instant; may be real or digital Motion Image — n Motion Image — a sequence of images that, when viewed consecutively at the appro- priate rate, gives the impression of con- tinuous motion; may be digital or analog

17 Theoretical Foundations of Multimedia Chapter 3 Scanners Schematic Drawing of a Scanner

18 Theoretical Foundations of Multimedia Chapter 3 Digital Cameras Schematic Drawing of a Digital Camera

19 Theoretical Foundations of Multimedia Chapter 3 Digital Cameras and Scanners n Quality of the optics and the scanning mechanism, which determines focus Precision of the photosensitive cells, which determines the accuracy of the encodingof intensity and wavelength data n Precision of the photosensitive cells, which determines the accuracy of the encodingof intensity and wavelength data Resolution of the instrument in dots per inch, which determines graininess n Resolution of the instrument in dots per inch, which determines graininess Amount of storage available, which deter- mines the total size of an image that canbe digitized n Amount of storage available, which deter- mines the total size of an image that canbe digitized Image quality depends on the:

20 Theoretical Foundations of Multimedia Chapter 3 Inputting Images Memory required to store a 5” x 7” snapshot Dots/inch resolution of snapshot image Bytes required for storage 1.05 Mb 9.45 Mb 37.8 Mb Mb Assuming no compression, 24 bits per pixel

21 Theoretical Foundations of Multimedia Chapter 3 Video Cameras and Frame Grabbers n Video cameras are similar to digital cameras n Except that a video camera takes image after image continuously n The output from many video cameras is analog and requires digitizing circuitryto make the image usable in a computer n Digital camcorders are now available n Frame grabber software allows the capture ofa single still image from the video stream n Frame grabbed images are of rather low resolution, however, <80-90 dots/inch

22 Theoretical Foundations of Multimedia Chapter 3 Microphones and MIDI Keyboards n For input of sound n Microphones capture sound waves from theair as an analog signal n The analog signal must be digitized to be stored and then replayed by the computer n Digitizing at <10,000 Hz is adequate for speech; 20,000 Hz is needed for music n MIDI keyboards usually look like piano key- boards with extra switches and controls n MIDI keyboards encode and transmit musical information according to the MIDI standard

23 Theoretical Foundations of Multimedia Chapter 3 Inputting Positional Information n Mice n Trackballs n Track pads n Joysticks n Drawing tablets

24 Theoretical Foundations of Multimedia Chapter 3 Inputting Positional Information n Specifying a point on a surface requires two dimensions, as with latitude and longitude n A third dimension could be added, as with altitude n For multimedia, what is commonly needed is position on the monitor in terms of left-right (X) and up-down (Y) distances

25 Theoretical Foundations of Multimedia Chapter 3 Inputting Positional Information n X and Y coordinates are obtained relative to a fixed point, usually one corner of the screen n The coordinates are entered in analog form as output from roll- ing wheels inside a device such as a mouse n The analog values are digitized to specify the X and Y coordinates

26 Theoretical Foundations of Multimedia Chapter 3 The Mechanism of a Mouse

27 Theoretical Foundations of Multimedia Chapter 3 Using a Drawing Tablet

28 Theoretical Foundations of Multimedia Chapter 3 Created in part using a drawing tablet Created in part using a drawing tablet © Janet Anderson Collage by Janet Anderson

29 Theoretical Foundations of Multimedia Chapter 3 CD-ROMs, DVDs, and Video Disks n Media for external storage and transport of data u Compact disk—read-only memory u Rewritable compact disk (CD-RW) u DVD u Video disk (laser disk); analog format

30 Theoretical Foundations of Multimedia Chapter 3 CD-ROMs CD-ROMs n Digital format n Write once, read many times n A rewritable version (CD-RW) is available, but not in common use n Information is “written” by burning tiny holes in the disk surface with a laser n The hole pattern is read by a laser and inter- preted as the bits comprising the data n Can store megabytes of data; about 300,000 pages of double-spaced text, or more than an hour of high fidelity sound

31 Theoretical Foundations of Multimedia Chapter 3 Creating Multimedia CD- ROMs n Requires a hard disk large enough to store ~650 megabytes of data to be writtento the CD n Requires a CD-ROM recorder that writes the data to the blank CD using a laser n The developer creates the multimedia mater-ial, stores it on the hard disk, and then tests it as completely as possible n When the material is in final form, it is written to the blank CD as if it were being copied from one disk to another

32 Theoretical Foundations of Multimedia Chapter 3 Video Disks or Laser Disks n Much larger than a CD-ROM; ~12” in diameter n Hold ~54,000 video frames per side n Hold ~30 minutes of video per side n Read-only n Analog format n Requires a conversion board to be used with a computer n Excellent for large-scale, video-based multimedia projects

33 Theoretical Foundations of Multimedia Chapter 3 Virtual Reality Devices Non interactive Slow image update rate Simple image Nonengaging content and presentation No sound Basic Screen display Low resolution image Monoscopic image Small field of view No head tracking No body motion sensing No tactile feedback Highly interactive Fast image update rate Highly complex image Highly engaging content and presentation Three-dimensional sound Head-mounted display High resolution image Stereoscopic image Full field of view Full head tracking Full body motion sensing Full tactile feedback Factors affecting the degree of immersion in virtual reality

34 Theoretical Foundations of Multimedia Chapter 3 NCSA’s CAVE

35 Theoretical Foundations of Multimedia Chapter 3 NCSA’s CAVE Virtual Reality Room with stereo glasses and magnetic head/hand tracking Fully immersive using three of four walls to display the graphics Uses an SGI Power Onyx with Reality Engine 2 software

36 Theoretical Foundations of Multimedia Chapter 3 NCSA’s ImmersaDesk Miniature version of NCSA’s CAVE

37 Theoretical Foundations of Multimedia Chapter 3 NCSA’s ImmersaDesk Drafting-table format virtual prototyping device

38 Theoretical Foundations of Multimedia Chapter 3 NCSA’s ImmersaDesk Uses CAVE’s stereo glasses and magnetic head/hand tracking

39 Theoretical Foundations of Multimedia Chapter 3 NCSA’s ImmersaDesk Semi-immersive, fills the user’s field of vision

40 Theoretical Foundations of Multimedia Chapter 3 NCSA’s ImmersaDesk Uses an identical SGI Power Onyx with the same Reality Engine 2 software as the CAVE

41 Theoretical Foundations of Multimedia Chapter 3 VR Head-Mounted Display

42 Theoretical Foundations of Multimedia Chapter 3 VR Head-Mounted Display Limitations: n Liquid Crystal Displays (LCDs) u pixels not as small as a CRT u pixels not as bright as a CRT u cannot change as quickly as a CRT u short focal distance makes precision, high resolution, and rapid response even more essential n Muscle receptor feedback confusion u light rays indicate “distant” u muscles indicate “very close”

43 Theoretical Foundations of Multimedia Chapter 3 VR Head-Mounted Display n Parallax — the apparent change in position of a stationary object when viewed from slightly different positions n A person’s eyes each see a slightly different view of an object n As the brain receives these two images, it interprets the the distance to the object in terms of the difference in position of the object in the two images n Parallax can be used to fool the brain into “seeing” images as being at various distances

44 Theoretical Foundations of Multimedia Chapter 3 Demonstrating Parallax Pencil Looking at a pencil aligned What is seen using with the corner of a room both eyes What is seen with right eye covered left eye covered

45 Theoretical Foundations of Multimedia Chapter 3 Stereoscope Courtesy of Special Collections, M. I. King Library, University of Kentucky

46 Theoretical Foundations of Multimedia Chapter 3 Parallax Problems with VR Head-Mounted Displays n Images may not be perfectly realistic, especially with motion images n When the observer’s head moves and the eyes are refocused, muscle receptor feedback data does not correlate with visual cues n The perspective is always that of the camera, never the viewer’s eyes n A viewer motion feedback mechanism is needed to change the perspective n This all contributes to “cybersickness ”

47 Theoretical Foundations of Multimedia Chapter 3 VR Aural Output n Refer to the discussion in chapter 2 regarding the perception of sound n Two key factors u Localization u Identification n The brain interprets differences in the signals it receives from the two ears in a manner analogous to binocular vision n For multimedia sound to be completely realistic, it requires head-position sensing feedback and enormous computational power — not practical for most multimedia

48 Theoretical Foundations of Multimedia Chapter 3 VR Input Devices The terminology of three-dimensional motion y x z Origin Roll Yaw Pitch

49 Theoretical Foundations of Multimedia Chapter 3 VR Position Sensing n A point in space is defined in terms of distance along three mutually perpen-dicular axes, usually termed X, Y, and Z n Motion is defined in terms of changes in position, which requires six parameters n Devices that can sense and record motion are termed six-degrees-of-freedom (6-DOF) devices

50 Theoretical Foundations of Multimedia Chapter 3 VR Position Sensing n Sensor output from a 6-DOF device can be u continuous u polled, or sent only upon request n Parameters to consider in evaluating a tracking device: u Lag or Latency — the delay between the actual time of the motion and when it is available as input data; should be <50 mSec u Update rate — Rate at which measurements are made; should be as fast as possible u Precision or accuracy of the measurements u Range over which the sensors operate u Rejection of interference

51 Theoretical Foundations of Multimedia Chapter 3 VR Voice Input n Speech Recognition n Complications due to variations in u Pitch u Timbre u Volume u Speed of Delivery u Inflection u Accent n Natural language processing

52 Theoretical Foundations of Multimedia Chapter 3 Natural Language Processing n Put out the light. n Turn off the light. n Close the light, please. n The light, turn it off. n Please, shut the light. n Kill the lights.

53 Theoretical Foundations of Multimedia Chapter 3 Natural Language Processing n Only the son praised his sister. n Only the son praised his sister. (The rest of the family did not.) n The only son praised his sister. n The only son praised his sister. (There was just one son.) n The son only praised his sister. n The son only praised his sister. (He never found fault with her.) n The son praised only his sister. n The son praised only his sister. (But never anyone else.) n The son praised his only sister. n The son praised his only sister. (He had just one sister.) n The son praised his sister only. n The son praised his sister only. (In this instance, he praised no one but her.)

54 Theoretical Foundations of Multimedia Chapter 3 Modems and Network Interfaces n Serial and Parallel u Serial — the bits arrive sequentially u Parallel — the bits arrive simultaneously Character encoding n Character encoding u ASCII — American standard code for information interchange u EBCDIC — Extended binary-coded decimal interchange code u Unicode

55 Theoretical Foundations of Multimedia Chapter 3 ASCII and Unicode n ASCII is limited because it is only a 7- or 8-bit code; even using “escape sequences” only a small number of characters can be encoded n Unicode is a 16-bit code that can encode many primary scripts plus special character sets known as secondary scripts

56 Theoretical Foundations of Multimedia Chapter 3 Unicode Scripts Primary scripts: ArabicGeorgianHebrewMalayalam ArmenianGreekHiraganaOriya BengaliGujaratiKannadaPhonetic BopomofoGurmkhiKatakanaTamil CyrillicHanLatinTelugu DevanagariHangulLaoThai Secondary scripts: NumbersGeneral diacritics General symbolsMiscellaneous symbols General PunctuationTechnical symbols DingbatsMathematical symbols Presentation forms Arrows, blocks, box drawing forms, and geometric shapes

57 Theoretical Foundations of Multimedia Chapter 3 Modems and Network Interfaces n Start bits u Opposite bit from the system idle state u Necessary to alert the receiver to the beginning of a new character Stop bits n Stop bits u Provide a short delay at the end of each character to give the receiver enough time to convert from serial to parallel n Error-checking codes u Parity bits, CRC bits, etc. u Discussed in chapter 6

58 Theoretical Foundations of Multimedia Chapter 3 Modems and Network Interfaces n Transmission rate u Internal transfer rates are much faster than data rates over networks u The interface needs to “interrupt” the computer when it has new data, not keepit from doing other processing whiledata is being received n Transmission form u Connection via a telephone line requires a modem (MOdulator-DEModulator) to translate the internal data transfer format into an audio signal, and vice- versa

59 Theoretical Foundations of Multimedia Chapter 3 Modems and Network Interfaces Use of modems and telephone lines for connectivity


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