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Berkeley Multimedia Research Center September

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					   Video Fundamentals

           September 9, 1999


         Lawrence A. Rowe
      University of California, Berkeley
URL: http://www.BMRC.Berkeley.EDU/~larry


          Copyright @1999, L.A. Rowe
                                      Outline
  • History
  • Broadcast System Elements
  • Scanning and Interlace
  • Color and Gamma
  • Chroma Subsampling
  • Representations


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                                      History

• 1839: Daguerreotype Cameras
• 1893: Telephone Audio Broadcasting (Puskas)
• 1895: Wireless Communication (Marconi,
  Popov)
• 1895: Film Presentation (Lumiere Brothers)
• 1919: Radio Broadcasting (Holland, Canada)
• 1934: US establishes FCC
• 1935: TV Broadcasting (Germany, Britain)
• 1941: US B&W TV
                                        ADD: telephone invention, founding of ATT, tv inventions,
                                        first radio networks/stations



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                          History (cont.)

• 1951: Videotape Recorder (Bing Crosby
  Enterprises)
• 1953: US Color TV (NTSC)
• 1963: Geostationary Satellites
• mid ‘70s: Fiber Optic Transmission - cable
• 1985: FCC establishes ATSC - standard by 1993?
• 1989: Analog HDTV Broadcasting (Japan)
• 1996: ATSC Standard Adopted

                                       ADD: first ntsc tv broadcasts, 1st cable system, consumer vcr,
                                       tivoli/replay device, direct tv, first hdtv broadcasts

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                     Standards Groups
• ITU-T – ITU Telecommunications
        Formerly CCITT
• ITU-R – ITU Radiocommunications
        Formerly CCIR
• FCC
• SMPTE - Society of Motion Picture and
  Television Engineers
… and many more!

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                     Broadcast System



                          Transmitter




                                        Receiver
        Goals:
             1. Efficient use of bandwidth
             2. High viewer perception of quality

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              Scanning and Interlace
• Transmission is continuous signal
        Transmitter captures images and encodes
        Receiver decodes for display
• Image traced out line-by-line
        Left-to-right top-down scanning
        vertical/horizontal blanking interval
• Signal is interlaced
        Improves perception of motion (?)
        Alternative is progressive scanning


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               Video Display Scanning
         Amplitude                       Cathode




                                  Time


 • Video composed of luma and chroma signals
 • Composite video combines luma and chroma
 • Component video sends signals separately


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                     Camera Operation
                                 Color     Camera
                                 Filters    Tubes
Zoom
                                       R                      Luma
 Lens




                                                    Encoder
                Beam
                Splitter              G
                                                              Chroma
                                      B



• Camera has 1, 2, or 3 tubes for sampling
• More tubes (CCD’s) and better lens produce
  better pictures

Multimedia Systems and Applications                               9
                        Direct View CRT
  • Three guns (RGB) energize phosphors
          Varying energy changes perceived intensity
          Different energies to different phosphors
          produces different colors
          Phosphors decay so you have to refresh
  • Different technologies
          Shadow mask (delta-gun dot mask)
          PIL slot mask
          Single-gun (3 beams) aperture-grille (Trinitron)


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Aperture-grille –vs- Shadow Mask



                                 R
                                 G    R
                                  B       G
                                      B




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                     Scanning Notation

   • Lines/”frame rate” specification
           NTSC          525/59.94
           PAL           625/50
   • ATSC – everything is variable
           1080i         1920x1080 interlaced scanning
           720p          1280x720 progressive scanning
   • Why 59.94?
           Avoids interference problem between color
           and sound subcarrier


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                       Interlaced Fields
                 Signal Format
    Line 1 ---
                 vertical blanking
   Line 21 ---
                                                Raster Format
                      Field 1                                           1
                                                                        2
                                                                        3

                                      485
  Line 263 ---                                                          ...
                 vertical blanking
                                      485
  Line 283 ---                        2
                                      4
                                                                        484
                                      ...
                                                                        485
                     Field 2
                                              ITU-R Rec. 601: 720x483
                                        484
  Line 525 ---

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                   Scanning (525/59.94)
                                        Total Size   Active Area
square
                                         780X525      644X483
 pixel                  Active



 601                                     858X525      720X483
                       Active



 4fsc                                    910X525      757X483
                      Active

  Multimedia Systems and Applications                           14
         Aspect Ratio/Refresh Rate
• Aspect ratio
        Conventional TV is 4:3 (1.33)
        HDTV is 16:9 (2.11)
        Cinema uses 1.85:1 or 2.35:1
• Refresh Rate
        NTSC is 60Hz (59.94Hz)
        PAL is 50Hz
        Cinema is 48Hz (but still only 24 fps)


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                            NTSC Video
                        (525-lines, 60-fields/sec)
• 525 scan lines repeated 29.97 times per
  second (i.e.33.37 msec/frame)
• Interlaced scan lines divide frame into 2
  fields each 262.5 lines (i.e.16.68 msec/field)
• 20 lines reserved for control information at
  the beginning of each field
    Only 483 lines of visible data
    Laserdisc and S-VHS display around 420 lines (perception)
    Normal broadcast TV displays around 320 lines (“)
• Line lasts 63.6 usec(10.9 usec blanked)

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                               PAL Video
                        (625-lines, 60-fields/sec)

• 625 scan lines repeated 25 times per
  second (i.e. 40 msec/frame)
• Interlaced scan lines divide frame into 2
  fields each 312.5 lines (i.e. 20 msec/field)
• Approximately 20% more lines than NTSC
• NTSC vs. PAL  roughly same bandwidth



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                         Color Perception
• Color is perceived lightwave
     400nm to 700nm received at retina
     Humans more sensitive to brightness than color
• Retina composed of cones and rods
     Cones respond to different frequencies (RGB)
     Rods measure brightness at low light levels
     (i.e., nightvision)
• CIE established standards for color
     CIE XYZ, CIE xyY  Linear RGB


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                                      Gamma
• CRT is inherently non-linear
      Display changes based on voltage driving it
• Human vision is also non-linear
      Lightness sensation is a power function of
      intensity (y=xw)
• Serendipity happens…
      Non-linear CRT close to inverse human lightness
      Coding intensity into a gamma corrected
      signal maximizes perceptual image
• Y -vs- Y’
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                        Gamma in Video




                           camera              transmission   display

• Camera performs gamma correction
• Display imposes inverse power function
                                      y = x 1/0.45


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                   Color Image Coding

• Image represented by 24 bit pixel (8 bpp)
        Each color value between 0 and 255
• Video uses non-linear coding
        Uniform distribution of colors to codes
        RGB  R’G’B’ (gamma corrected RGB)
• Video uses luminance/chromance
        R’G’B’  Y’CBCR
        Luminance is Y (technically luma is Y’)
        Chromance is CBCR

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                                      Jargon

• CBCR actually color difference signals
       CB is scaled version of (Y’-B’)
       CR is scaled version of (Y’-R’)
• Confusing terms: YUV, YIQ, Y CBCR,…
       Scaled versions of <Y’, Y’-B’, Y’-R’>
       Green has highest contribution to luminance
• Luminance –vs- Luma (i.e., Y –vs- Y’)
       Y is linear luminance
       Y’ is gamma corrected luminance (aka luma)


Multimedia Systems and Applications                  22
                  Chroma Subsampling

• Chroma subsampling reduces data
        2 chroma/luma  16 bpp
        1 chroma/luma  12 bpp
• Notation is a:b:c
        a is luma samples
        b is chroma samples per odd line
        c is chroma samples per even line
• Ex. 4:4:4, 4:2:2, 4:1:1, 4:2:0, …

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                           Line Sampling
                       Y          Y           Y   Y        Y
     4:4:4
                  CR/CB CR/CB CR/CB CR/CB CR/CB
                    Y    Y     Y     Y     Y
     4:2:2
                  CR/CB                  CR/CB          CR/CB
                    Y             Y        Y      Y       Y
     4:1:1
                                      CR/CB
         4:2:2 is referred to as broadcast quality
         4:1:1 is referred to as VHS quality
         4:2:0 is 2:1 down sampling in horizontal and vertical direction
Multimedia Systems and Applications                                        24
                         4:2:0 Sampling




             Luma sample
             Chroma sample

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                        Representations
• Composite
        NTSC - 6MHz (4.2MHz video), 29.97 frames/second
        PAL - 6-8MHz (4.2-6MHz video), 50 frames/second
• Component
        Separation video (luma, chroma) - svhs, Hi8mm
        RGB, YUV, YIQ, …
        YCBCR - used for most compressed representations
• Separation video called “s-video”


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      Analog Video Representations

• NTSC
     Y = 0.299R + 0.587G + 0.114B
     I = 0.596R - 0.275G - 0.321B
     Q = 0.212R - 0.523G + 0.311B
     composite = Y + Icos(Fsc t) + Qsin(Fsc t)
• PAL
     Y = 0.299R + 0.587G + 0.114B
     U = 0.492(B-Y)
     Q = 0.877(R-Y)
     composite = Y + Usin(Fsc t) + Vcos(Fsc t)



Multimedia Systems and Applications              27
                                 Digitizing

• Analog TV is a continuous signal
• Digital TV uses discrete numeric values
        Signal is sampled
        Samples are quantized
        Small, discrete regions are digitized
• Image represented by pixel array



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                                     Image Sizes
             160 352           720       800          1152   1280   1920

         QSIF
         (19Kp)
120
        SIF (82Kp)
240

             601 (300Kp)
483
                  SVGA (500Kp)
600

                            ATV (1Mp)
720
                           Workstation (1Mp)
900
                                         HDTV (2Mp)
1080

       Multimedia Systems and Applications                                 29
                  Workstation Images?
• [1 Mega Pixel] 1152 x 900 = 1,036,800 pixels


• [xvga] 1024 x 768                     = 786,432 pixels


• [?]           1280 x 1024            = 1,310,720 pixels




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      Digital Video Representations
• Digital Composite Video(D2/D3,SMPTE 244M)
    142 Mb/s data rate, either parallel or serial
    Subsampled color signals 4:2:2
• Digital Component Video(D1/D5,SMPTE RP125)
    Maintain separate signals for luma and chroma
    270 Mb/s data rate, either parallel or serial
    Subsampled color signals 4:2:2
• Compressed Digital Video
    MPEG, MJPEG, H.26x, DV, …


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      Digital Video Block Structure
                                      macroblock


 • 4:2:2 YCBCR                        Y1      Y2    CB1   CR1
         16x16 macroblock              Y3 Y4       CB2 CR2
         8x8 pixel blocks
         8 bits/sample = 16 bits/pixel = 4Kbits/macroblock
 • 4:1:1 YCBCR
         3Kbits/macroblock
         12 bits/pixel
                                      Y1       Y2
                                                    CB    CR
                                      Y3       Y4



Multimedia Systems and Applications                             32
          What is Video Data Rate?
• Digital
         720x483 = 347,760 pixels/frame
         4:2:2 sampling gives 695,520 bytes/frame
         21 MB/sec (167 Mbs)
         4:4:4 sampling gives 250 Mbs
• ATV (MPEG MP@ML)
         1280x720 = 921,600 pixels/frame
         4:2:0 sampling gives 1,382,400 bytes/frame
         41 MB/sec (328 Mbs)

              (Note: MPEG coded streams are 1.5-80 Mbs)



Multimedia Systems and Applications                       33
What is Video Data Rate (cont.)?

• ATSC (720P)
        720x1280 = 921,600 pixels per frame
        4:2:2 sampling = 1,843,200 bytes per frame
        24 fps = 44,236,800 bytes per second
         44 MB/s = 354 Mbs
• ATSC (studio 1080I)
        1080x1920 = 2,073,600 pixels per frame
        4:4:4 sampling = 6,220,800 bytes per frame
        30 fps = 186,624,000 bytes per second
        187MB/s = 1.5 Gbs



Multimedia Systems and Applications                  34
             Serial Digital Data Rates
• Serial digital is a video transport standard
       Widely used in broadcast and production studios
• Data rates
       NTSC SDI approximately 200 Mbs
       ATSC SDI approximately 1.5 Gbs
• Routing Switcher
       Remember typical facility might have a 256x256
       routing switcher
       What is data rate across the switch?


 Multimedia Systems and Applications               35
                       Human Perception
•What is smooth motion
   Depends on source material
   Most action is perceived as smooth at 24 fps
•Human most sensitive
   Low frequencies
   Changes in luminance and blue-orange axis
•Vision emphasizes edge detection
   Strong bias to horizontal and verticle lines
•Visual masking by large luminance changes

 Multimedia Systems and Applications              36
      Producing High Quality Video
• Need high quality camera
     S-Video(SVHS, Hi8mm) better than composite
     3 chips better than 1 chip
     Digital better than analog
• Lights, lights, lights…
     Experiment with filters to change apparent colors
• Shoot scene from different angles and cut
  between them to create visual stimulation
• Study film/video techniques
     Let person exit the scene without moving camera
     Keep orientation of images correct
     Change scene/shot to reflect time change

Multimedia Systems and Applications                      37
                              Conclusions
• NTSC/PAL were excellent standards that
  lasted over 50 years
         Technology has changed dramatically during
         this time
• Digital revolution is changing industry
         Main impact is development of ATSC standard
• Internet revolution is also chaning industry
         Webcasting –vs- mass market broadcasting
         Wireless –vs- cable –vs- packet transmission

Multimedia Systems and Applications                     38

				
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