MM_Chapter5

• Analog video


  An analog signal f(t) samples a time-varying image
• Progressive scanning


  • Traces through a complete picture (a frame) row-wise for each time interval
• Interlaced scanning


  • The odd-numbered lines are traced first, and then the even-numbered lines are traced. This results in "odd" and "even" fields - two fields make up one frame.
• The odd lines (starting from 1) end up at the middle of a line at the end of the odd field, and the even scan starts at a half-way point.
• Horizontal retrace


  The jump from Q to R, during which the electronic beam in the CRT is blanked.
• Vertical retrace


  The jump from T to U or V to P
• Because of interlacing, the odd and even lines are displaced in time from each other
• Interlaced scan produces blurring of fast moving objects.
• De-interlacing


  Various schemes used to convert interlaced video to non-interlaced
• The simplest de-interlacing method consists of discarding one field and duplicating the scan lines of the other field, but this results in complete loss of information in one field.
• Analog video


  Uses a small voltage offset from zero to indicate "black", and another value such as zero to indicate the start of a line
• NTSC video

  National Television System Committee standard used in North America and Japan, with 4:3 aspect ratio, 525 scan lines per frame at 30 frames per second, interlaced scanning
• NTSC has 262.5 lines per field.
• NTSC video has 485 active video lines per frame, with the rest used for vertical retrace and sync
• Even with non-interlaced scan, NTSC TV is only capable of showing about 340 (visually distinct) lines. With interlaced scan, this could be lower.
• NTSC video


  An analog signal with no fixed horizontal resolution, requiring a "pixel clock" to divide each horizontal line into samples
• PAL video


  Phase Alternating Line standard used in Western Europe, China, India, and many other parts of the world, with 625 scan lines per frame, 25 frames/second, 4:3 aspect ratio, interlaced fields, YUV color model
• SECAM video


  Système Electronique Couleur Avec Mémoire, the third major broadcast TV standard, also using 625 scan lines per frame, 25 frames per second, 4:3 aspect ratio, interlaced fields. It differs from PAL in the color coding scheme, with U and V signals modulated using separate color subcarriers and sent in alternate lines.
• 360 Video

  Also known as Omnidirectional Video, Spherical Video or Immersive Video
• 360 Video

  • Can span 360° horizontally and 180° vertically
  • Captured by cameras at (almost) all possible viewing angles
  • Can be monoscopic (single perspective) or stereoscopic (multi perspective)
• Capturing of 360° Video

  • Omnidirectional camera (a camera that can capture a circular field of view). Less popular.
  • Multiple cameras with a wide field of view. More popular.
• 360 Video Projections

  1. Equirectangular Projection: or single perspective which is the most popular.
  2. Cubemap Projection: to reduce the distortion, projections are made onto the six faces of the cube.
  3. Equi-Angular Cubemap: the projection intervals are remapped to new intervals of equal lengths. Adopted by Google.
  4. Pyramid Format: The base of the pyramid provides the full resolution image of the front view. The sides of the pyramid provide the side view images with gradually reduced resolutions. Advocated by Facebook.
• Advantages of digital video

  • Can be stored on digital devices, processed, integrated with multimedia, direct access for nonlinear editing, no quality degradation from repeated recording, easier encryption and better tolerance to channel noise
• Chroma subsampling


  Decimating the chrominance signal since humans see color with much less spatial resolution than black and white
• 3D video


  Enables the experience of immersion.
• Chroma subsampling schemes

  1. 4:4:4 (no subsampling)
  2. 4:2:2 (horizontal subsampling by factor of 2)
  3. 4:1:1 (horizontal subsampling by factor of 4)
  4. 4:2:0 (horizontal and vertical subsampling by 2) -> commonly used in JPEG and MPEG
• ERP has severe distortions, especially near the poles
• CCIR

  Consultative Committee for International Radio, one of the most important standards it has produced is CCIR-601, for component digital video.
• Other Projections for 360° Video

  • Cubemap Projection (CMP)
  • Equi-Angular Cubemap (EAC)
  • Pyramid Format
• 3D Video and TV

  Three-dimensional (3D) pictures and movies that enable the experience of immersion
• CIF


  Common Intermediate Format specified by the CCITT.

  Used to specify a format for lower bitrate.

  Same as VHS quality and uses progressive scan.

  QCIF is Quarter-CIF.
• High Definition TV (HDTV)

  The main thrust of HDTV is not to increase the “definition” in each unit area, but rather to increase the visual field especially in its width.
• Monocular Cues for 3D Percept

  • Shading
  • Perspective scaling
  • Relative size
  • Texture gradient
  • Blur gradient
  • Haze
  • Aerial perspective
  • Occlusion
  • Motion parallax
• Occlusion and Motion parallax are more effective monocular cues for 3D percept
• Binocular Cues for 3D Percept

  • Stereo vision (Stereopsis)
  • Interocular distance (the distance between the left and right eyes, around 65mm)
  • Disparity (the shift between the left and right eye views)
• HDTV

  The first generation of HDTV was based on an analog technology.

  Has 1,125 scan lines, interlaced (60 fields per second) scanning, and 16:9 aspect ratio.
• Current 3D video/TV systems are almost all based on stereopsis because it is believed to be the most effective cue
• ITU-R-601

  International standard for professional video applications, adopted by certain digital video formats including the popular DV video
• Simple Stereo Camera Model

  • The left and right cameras are identical, with parallel optical axes pointing in the Z-direction
  • Disparity d = (b*f)/Z, where b is the baseline length and f is the focal length
• Toed-in Stereo Camera Model


  • Similar to human vision system, with eyes rotating around a vertical axis to obtain single binocular vision (vergence)
  • Disparity d = 0 at the object of focus, positive parallax for farther objects, negative parallax for nearer objects