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Chapter Five Fundamental Concepts in Video

Chapter Five Fundamental Concepts in Video. In the recent lecture: Types of Video Signals Analog Video Digital Video. Three Video Market Segment. Types of Video Signals. Component Video: 3 Separate wires: luminance + 2 color difference Signals (Y, P B , P R ),

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Chapter Five Fundamental Concepts in Video

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  1. Chapter Five Fundamental Concepts in Video

  2. In the recent lecture: • Types of Video Signals • Analog Video • Digital Video

  3. Three Video Market Segment

  4. Types of Video Signals Component Video: • 3 Separate wires: luminance + 2 color difference Signals (Y, PB, PR), PB=R-Y, PR=B-Y • Used in most Computer Systems SVGA (Super Video Graphics Array) is one of the best and most widely used video signal types • The primaries can either be RGB or a luminance-chrominance transformation of them (e.g., YIQ, YUV). • Best color reproduction • Requires more bandwidth and good synchronization of the three components

  5. Types of Video Signals Composite Video: • Video-only components of for one channel on one wire • color (chrominance) and luminance signals are mixed into a single carrier wave. • Some interference between the two signals is inevitable. • Used in NTSC (YIQ)

  6. Types of Video Signals S-Video: • Separated video --- a compromise between component analog video and the composite video. • It uses two lines, one for luminance and another for composite chrominance signal. • Used in S-VHS

  7. Types of Video Signals Composite Video Component Video • Component Video is native format for digital TV since MPEG compression operates on component video • Component video does away with several artifacts of composite video

  8. Analog Video Analog videoAnalog means that the video signal is transmitted by a high-frequency wave. Changing the wave's amplitude represents the different colors shown on the screen. Analog video is found in most older computer video displays, as it is the original standard to transmit video over coaxial lines. Digital videoDigital means that the video signal is transmitted in ones and zeros. The transmission sends a very fast stream of data about each and every pixel on the screen.

  9. Analog Video Deflection coil: magnetically steers beam in a left-to-right top-to-bottom excited by electron beam, intensity of beam determines brightness

  10. Analog Video Scanning Methods (Display Modes) Interlaced • odd lines are displayed first, then even lines • Taken together, all the odd lines are called a field (and similarly for all the even lines). • The original purpose of interlaced display was to avoid flicker. • Standard television uses this method, displaying 60 fields per second (which makes 30 frames per second). • Half Band width required.

  11. Scanning Methods (Display Modes) Analog Video Progressive • The method used by computer monitors. • An entire screen can be written to a buffer. • The buffer is displayed “instantaneously.”

  12. Analog Video Scanning Methods(Display Modes)

  13. Analog Video 17

  14. Active Analog Video Scanning Methods(Display Modes)

  15. Analog Video:Representation NTSC Video �National Television Systems Committee � 525 scan lines per frame, 30 (29.97)fps (33.37 µsec/frame). � Interlaced, each frame is divided into 2 fields, 262.5 lines/field, , 4:3 aspect ratio. � 20 lines reserved for control information at the beginning of each field � So a maximum of 485 lines of visible data • Laserdisc and S-VHS have actual resolution of ~420 lines • Ordinary TV --~320 lines • Each line takes 63.5 microseconds to scan. � Color representation: • Uses YIQ color model.

  16. Analog Video: Decoding NTSC • Cheapest method: low pass filter with 3MHz cutoff to get rid of chroma • But also removes some of the high frequency luminance data, and blurs the image • If some color signal remains in the recovered Y values, it will look like dots crawling up vertical edges – “chroma crawl” • If some luminance signal remains in the separated chroma values, it will appear that rainbows are superimposed on what should be monochrome

  17. Analog Video:Representation PAL (SECAM) Video � Phase Alternating Line � 625 scan lines per frame, 25 frames per second, , 4:3 aspect ratio (40 µsec/frame) � Interlaced, each frame is divided into 2 fields, 312.5 lines/field � Color representation: • Uses YUV color model

  18. Analog Video:Representation SECAM �Système Electronique Couleur Avec Mémoire �625 scan lines per frame, 25 frames/s, 4:3 aspect ratio �R-Y and B-Y information is transmitted (sequentially) in alternate lines, and a video line store is used to combine the signals together  the vertical color resolution is halved relative to PAL and NTSC � differs from PAL in the color coding scheme � Color representation: Uses YUV color model

  19. SummaryStandards Organizations for Video (originally analog, extended to digital) Analog Video

  20. Analog Video 24

  21. Digital Video • Digital video signal consists of luminance and chrominance information • Luminance – brightness, varying from white to black (abbreviated as Y) • Chrominance – color (hue & saturation), conveyed as a pair of color difference signals: • R-Y (hue & saturation for red, without luminance) • B-Y (hue & saturation for blue, without luminance) • Where’s the green?

  22. Digital Video: sampling

  23. Digital Video: sampling 4:2:0 sampling 4:2:2 sampling 4:1:1 sampling 4:2:2 – High End DV 4:2:0 – MPEG 1 & 2 4:1:1 – DV and DVCAM

  24. Digital Video: sampling Why not 4:4:4 sampling? • 720 x 486 resolution = 349,920 pixels per frame • 349,920 pixels x 10 bits/sample x 3 samples/pixel = 10,497,600 bits per frame • 10,497,600 bits/frame X 29.97 frames/second = 314,613,072 bits per second • 314,613,072 bps x 3600 seconds = ~141.58 GB/hour • For 1920x1080 HDTV, more like 840 GB/hour • 4:2:2 sampling drops that rate by a third ? with almost no perceptible difference in quality. • 4:2:0 and 4:1:1 drop it in half ? • about 70 GB/hour for normal resolution video

  25. Resampling: Resampling by interpolation is generally understood as the following procedure: • Prepare Original sample values. • Create new empty array with new dimensions using a proper geometric transformation method. • Interpolate new sample values of the above array (in 2) using sample values from original array (in 1). • Step 3 can performed using a suitable interpolation function. This can summarized in following equation:

  26. Resampling: Original coordinate of the original sample array Original sample value boundary of the function (kernel size) New coordinate of interpolated sample array kernel size interpolation function Interpolation sample value Fx calculated as follow: Fx = x × kx (Exact position (floating-point number)) x1 = Integer (Fx) ( Integer position (integer part of number)) Fx = Fx - x1 ( Fraction part of number (integer+fraction=exact)) kx represent magnification ratio

  27. Resampling: Digital Interpolation methods • Interpolation is a technique that pervades many an image application. • Let us ask why digital image interpolation? • To insert between or among others. • To change by putting in new configuration. • Image restoration by estimating a missing value by taking an average of known values at neighboring points. • For these reason, some of these interpolation methods will be cleared

  28. Resampling: Digital Interpolation methods Nearest-Neighbor Interpolation method • Nearest-neighbor interpolation method can summarized as follow: • Set the intensity of the interpolated pixel to the nearest-neighbor original pixel. • This method is very fast, but it produces aliasing or blocking effects along edges. • The function can be described by factor multiplied by the nearest pixel value (function kernel)

  29. Resampling: Digital image Interpolation example 33

  30. Digital Video Converting Analog Video to DigitalCCIR Standards for Digital Video • CCIR 601 (one standard for digital video) specifies a standard that applies to both NTSC and PAL. • According to the CCIR standard, a frame is sampled to 720 X 480 pixels for NTSC and 720 X 576 for PAL. • But this is misleading. There aren’t really 720 pixels per line. The number of samples taken to digitize the video doesn’t necessarily correspond to the number of pixels on the display device. • You can do digital video in NTSC format at 640 X 480 or 720 X 480 with different pixel aspect ratios. • You can do digital video in PAL format at 720 X 480 or 720 X 576 with different pixel aspect ratios.

  31. Digital Video Converting Analog Video to DigitalCCIR Standards for Digital VideoSub-Sampling • CCIR 601 prescribes 4:2:2 sub-sampling of the chrominance component. • This means that there in every 4-pixel-square area, 4 luminance samples are taken and 2 of each of the chrominance samples are taken (4 Y’ samples, 2 CB samples, and 2 CR samples).

  32. Digital Video H.261 Converting Analog Video to DigitalCCIR Standards for Digital VideoSub-Sampling • Real time constrain • Video conference cannot tolerate longer delays without becoming disjointed. • Maximum delay: 150 ms (about 7 frames/sec) • Picture format • CIF (Common Intermediate Format) • Component(size): Y(352  288), Cb & Cr(176  144) • Picture rate: 29.97 frames/sec • QCIF (Quarter CIF) • Component(size): Y(176  144), Cb & Cr(88  72)

  33. Video format Digital Video Picture format QCIF: Mobile video communication CIF:Videoconference CCIR: Standard Definition TV ATSC: High Definition TV

  34. Digital Video Video formats

  35. Why HDTV? Digital Video HDTV (High Definition TV) • Higher-resolution picture • Wider picture • Additional data • Easy to interface with computers

  36. Digital Television: SDTV, HDTV Digital Video HDTV (High Definition TV) • SDTV vs. HDTV • Standard definition television • High definition television • Is HDTV the same thing as digital TV? • No • Characteristics of HDTV • 16:9 aspect ratio (1280 X 720 or 1920 X 1080)

  37. Digital Video HDTV vs. DTV • High definition television is not necessarily digital – that is, it does not have to be digitally transmitted. • What characterizes HDTV is the aspect ratio, resolution, and sound quality • Digital television is not necessarily HDTV. • What characterizes DTV is the way in which the data is transmitted – in digital, as opposed to analog, form. • HDTV was not originally DTV, but at present most HDTV is digitally transmitted.

  38. Digital Video HDTV vs. DTV • There are 18 different DTV formats • 6 are also HDTV. • 5 of these (the DTV formats that are also HDTV) are based on progressive scanning and one 1 interlaced. • Both HDTV and DTV use MPEG-2 • Three of the 18 formats for DTV that are used frequently are: • 480p – 640 X 480 pixels, progressive • 720p – 1280 X 720 pixels, progressive • 1080i – 1920 X 1080 pixels, interlaced, why?

  39. Components of HDTV systems Display format Decoded video signals analog carrier + digital signals video signals Image Decoder Display Processor digital signals Demodulator De-multiplexer Audio Decoder Decoded audio signals audio signals

  40. Comparison Current TV HDTV

  41. Comparison (current TV)

  42. Comparison (HDTV)

  43. Typical Video System Chain

  44. Typical Video System Chain

  45. Typical Video System Chain

  46. Typical Video System Chain

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