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Multimedia Information Representation

Multimedia Information Representation. Analog Signals. Signal bandwidth and effect of bandlimiting channel. Analog signal and frequency components. Fourier transform and analysis. Signal encoder design. Associated wave form. Nyquist sampling theorem

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Multimedia Information Representation

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  1. Multimedia InformationRepresentation

  2. Analog Signals Signal bandwidth and effect of bandlimiting channel Analog signal and frequency components • Fourier transform and analysis

  3. Signal encoder design Associated wave form • Nyquist sampling theorem • In order to obtain an accurate representation of a time-varying analog signal, sampling rate >= 2 x highest sinusoidal frequency component • Nyquist rate Signal encoder

  4. Undersampling (< Nyquist rate) results in additional FC being generated that are not present in the original signal Cause the original signal to become distorted Need bandlimiting (antialiasing) filter Bandlimiting Filter

  5. Quantization Intervals Source of errors Quantization Interval q = 2Vmax / 2n Dynamic range of signal D = 20log10(Vmax/Vmin)dB Noise polarity

  6. Decoder Design

  7. Text • Unformatted text: plain text • ASCII character set • Mosaic character set used in Videotex and Teletext • Formatted text: richtext • Hypertext • Pages and hyperlinks • HTML, SGML

  8. Images: Graphics • Graphics: computer-generated images • Representation of a computer graphics • High-level version: e.g) PostScript • Bit-map format: GIF, TIFF

  9. Images: Digitized Documents

  10. Images: Digitized Pictures • Color principles Additive color mixing Subtractive color mixing

  11. Raster-scan principles

  12. Raster-scan Display Architecture • Pixel depth: # of bits per pixel • CLUT (color look-up table)

  13. Screen Resolution Visible lines per frame Digitization spatial resolution

  14. Digital Cameras and Scanners Color image capture RGB signal generation alternatives

  15. Audio • Speech signals: 50Hz ~ 10kHz • Nyquist rate = 20ksps • Music-quality audio: 15Hz ~ 20kHz • Nyquist rate = 40ksps

  16. PCM Speech Signal encoding and decoding Compressor Expander U-law : North America, Japan A-law: Europe and others Obtain 12-bit performance!!

  17. CD-DA (Digital Audio) standard Sampling rate: 44.1 ksps 16 bits/sample Bit rate for stereo music 2 channel x 44.1 ksps x 16 bits = 1.411 Mbps CD-quality Audio

  18. Synthesized audio • MIDI (Music Instruments Digital Interface) • A MIDI message = (status byte, data bytes, … ) • Music: sequece of message • Play out by the sequencer program or saved in a file • Need sound card

  19. Video Applications • Entertainment • Broadcast TV, VCR/DVD recording • Interpersonal • Video telephony, videoconferencing • Interactive • Windows containing short video clips

  20. Interlaced Scanning

  21. TV broadcast: Color Signals • Requirements • Color TV broadcast should be used by an existing monochrome (back-and-white) TV set • Color TV should be able to produce black-and-white pictures from monochrome broadcast • Properties of a color source • Brightness: amount of energy that stimulates the eye • Varies on a grayscale from back through to white (highest) • Independent of the color of the source • Hue(색조): actual color of the source • Each color has a different frequency/wavelength • Saturation(채도): strength or vividness of the color

  22. Luminance and Chrominance • Luminance: related to the brightness • Amount of white light • Same as the signal used by monochrome TV • Ys = 0.299Rs + 0.587Gs + 0.114Bs • Chrominance: related to the hue and saturation • Color difference signals i.e no brightness info. • Cb = Bs – Ys, • Cr = Rs – Ys

  23. Composite video signal • Magnitude of the two color differences are both scaled down • If the two color difference signals are transmitted, amplitude of luminance signal can become greater than that of the equivalent monochrome signal • PAL • Y = 0.299R + 0.587G + 0.114B • U = 0.493(B-Y) • V = 0.877(R-Y) • NTSC • Y = 0.299R + 0.587G + 0.114B • I = 0.74(R-Y) – 0.27(B-Y) • Q = 0.48 (R-Y) + 0.41(B-Y)

  24. Signal Bandwidth NTSC PAL

  25. TV Broadcast

  26. TV • Analog TV • Frame rate: # of frames per second produced by a video signal • common rate: 25 - 75Hz • Number of scan lines per frame • scan rate: # of lines scanned per second= frame rate x # of scan lines • Interlacing: to reduce the flickering • odd field, even field • Aspect ratio: width : height • Digital TV • convert analog signal to digital signal • sampling, quantization, coding

  27. Standard Frame rates Scan lines Aspect ratio Interlacing NTSC 29.97 525(480) 4:3 2:1 PAL 25 625(576) 4:3 2:1 SECAM 25 625(576) 4:3 2:1 Standard Analog TV Systems

  28. 4:2:2 format Studio-Quality TV: ITU-R 601 Bandwidth 6MHz sampling rate: 13.5MHz  720 samples / line Bit rate = 216Mbps (PAL, NTSC) Digital Video (I) Subsampling 4:2:2

  29. 4:2:0 format Bit rate = 162Mpbs HDTV format 16/9 aspect ratio: 1920 x 1152 pixel Refresh rate: 25Hz / 30Hz Studio application: 4:2:2 format Broadcast application: 4:2:0 format Digital Video (II)

  30. SIF (source intermediate format) VCR quality Used in MPEG-1 ½ resolution in both horizontal and vertical directions (by subsampling): 4:1:1 format ½ refresh rate (temporal resolution) Bit rate: 81Mbps CIF (common intermediate format) Videoconferencing quality Used in H.261 4:1:1 format Y = 360 x 288, Cb = Cr = 180 x 144 30Hz QCIF (quarter CIF) Video Phone Quality Used in H.261 Digital Video (III)

  31. PC Video

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