Multimedia Communication  

Multimedia signal processing is widely used in

• CD-ROM industry: VCD, DVD
• computer industry: image/graphic display device, audio device; video gaming device; virtual reality; computer vision; multimedia computer systems
• communication/telecom industry: videophone, teleconferencing, video/voice over packet-switched networks; mobile video devices
• TV industry: NTSC/PAL/SECAM analog TV, digital TV, HDTV
• Movie industry

Digital Video

• Advantages:
  • Direct random access --> good for nonlinear video editing
  • No problem for repeated recording
  • No need for blanking and sync pulse

  　

• Almost all digital video uses component video

  　

Chroma Subsampling

　

• How to decimate for chrominance?

• 4:2:2 --> Horizontally subsampled color signals by a factor of 2. Each pixel is two bytes, e.g., (Cb0, Y0)(Cr0, Y1)(Cb2, Y2)(Cr2, Y3)(Cb4, Y4) ...

  　

• 4:1:1 --> Horizontally subsampled by a factor of 4

  　

• 4:2:0 --> Subsampled in both the horizontal and vertical axes by a factor of 2 between pixels as shown in the figure.

  　

• 4:1:1 and 4:2:0 are mostly used in JPEG and MPEG (see Chapter 4).

ITU-R Standards for Digital Video

                       BT.601        BT.601         CIF         QCIF
                        525/60         625/50   
		         NTSC         PAL/SECAM       
--------------------  -----------    -----------   -----------  -----------

Luminance resolution   720 x 480      720 x 576     352 x 288    176 x 144

Chrominance resolut.   360 x 480      360 x 576     176 x 144     88 x 72

Color Subsampling        4:2:2          4:2:2   

Fields/sec                60             50            30           30

Interlacing               Yes            Yes           No           No 

• BT.601 uses interlaced scan, so each field only has half as much vertical resolution (e.g., 243 lines in NTSC). The BT.601 (NTSC) data rate is ~165 Mbps.

  　

• CIF (Common Intermediate Format) -- an acceptable temporary standard
  • Approximately the VHS quality
  • Uses progressive (non-interlaced) scan
  • Uses NTSC frame rate, and half the active lines of PAL signals --> To play on existing TVs, PAL systems need to do frame rate conversion, and NTSC systems need to do line-number conversion.

  　

• QCIF -- Quarter-CIF

ATSC Digital Television Standard

(ATSC -- Advanced Television Systems Committee) The ATSC Digital Television Standard was recommended to be adopted as the Advanced TV broadcasting standard by the FCC Advisory Committee on Advanced Television Service on November 28, 1995. It covers the standard for HDTV (High Definition TV).

Video Format

The video scanning formats supported by the ATSC Digital Television Standard are shown in the following table.

• The aspect ratio for HDTV is 16:9 as opposed to 4:3 in NTSC, PAL, and SECAM. (A 33% increase in horizontal dimension.)

  　

• In the picture rate column, the "I" means interlaced scan, and the "P" means progressive (non-interlaced) scan.

  　

• Both NTSC rates and integer rates are supported (i.e., 60.00, 59.94, 30.00, 29.97, 24.00, and 23.98).

Rate control

Rate control in video coding is to control the encoding process or encoding parameters (e.g., quantization step size) so as to achieve the target bit rate in the coded bit stream.