Digital video

1
Digital video

• Henning Schulzrinne
• Columbia University
• Fall 2003

2
Video sources

• VGA video (computer video output)
• component video
• R, G, B H (horizontal sync), V (vertical sync)
• Analog video from cameras
• NTSC or PAL coded color
• composite or component video
• Digital images
• scanners, copiers and fax machines
• digital cameras
• Images still pictures
• Video motion pictures

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Video types

• Bi-level images black and white
• fax, printed output (at pixel level)
• Gray level (monochrome) images
• Color (continuous tone)

4
Video compression

• unlike audio, no physiological model (masking)
• except lower color sensitivity than gray level
• statistical redundancy
• background correlation
• correlations across an image
• nearby pixel correlation
• frame correlation (motion compensation)
• subjective redundancy
• impact of different impairments
• block artifacts, noise, stair step (jaggies),

5
Bilevel (Fax) coding

• 1728 pixels per line
• one-dimensional run-length coding ? optimized for
  early memoryless fax machines
• Huffman coding
• 201 compression for simple text documents
• MREAD algorithm uses previous scan line
• improves compression to 251