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Digital video

Digital video. Henning Schulzrinne Columbia University Fall 2003. 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:

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Digital video

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  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

  3. 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 • 20:1 compression for simple text documents • MREAD algorithm uses previous scan line • improves compression to 25:1

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