Video Compression

1
Video Compression

• Is compression implemented with still images?
• Why does motion video require comnpression?
• Techniques implemented are based upon_________
• between _________, _________, and ________.
• Visibility- viewer ability for certain colour.

2
Video Compression Techniques

• SIMPLE
• Truncation reduces BPP, removes LSBs from
• every pixel.
• CLUT 8 bits only, therefore ______ colours.
• Run length coding- identifies strings of zero,
  assigns one value .

3
Video Compression

• Video Processing Engines a pool of algorithms
  that perform combinations of techniques on same
  image(adaptive).
• The input to a compression system is PCM and the
  output compression process is a ____ ___________.

4
Video Compression Techniques

• DPCM Differential pulse code modulation.
  Compares adjacent pixels and then transmits only
  difference between them.
• ADPCM Adaptive differential pulse code
  modulation. Quantizes with the feature of
  changing step sizes represented by difference
  bits.
• Transform Coding Converts a bundle of data into
  alternate form. Ex. DCT and Fourier.

5
Video Compression Techniques

• Full Motion Video Normal frame rates. Ex. 30
  fps.
• Video system must deliver a new image every 33
  ms.
• A CD rom fixed at 150,000 bytes/sec 5000 bytes
  per frame at 30 fps or 0.65BPP

6
Video Compression

• What is motion compensation?
• Identifies redundancies between frames.
• Form of frame to frame DPCM
• Pixel by pixel compare between 2 frames.
• Motion vector prediction based on a handful of
  lines and a few frames.
• Drawback! Almost always some pixel change.
• Remedy?___________________

7
Video Compression Types

• Two main types JPEG, MPEG
• JPEG ? still images
• ? AVI compression
• ? 2 frame types 1 KEY and 2
  DELTA
• ? Joint Photographic Experts
  Group
• Key?Delta?Delta?Key?Delta?Delta

8
Video Compression Types

• MPEG Motion Picture Experts Group
• ?3 frame types
• ? I, P, and B frames
• ? I frame (intra) compressed
  in ____
• ? serves as _______ for P and
  B
• ? P frames (__________)
  compares redundancies in images several frames
  apart.
• ? B frames (___________)
  targets redundancies in immediately preceding
  frame.

9
Video Compression Types

• GOP Group of Pictures
• I?B?B?P?B?B?P?B?B