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TTM4142 Networked Multimedia Systems Video Basics Image and Video Lossless Compression

TTM4142 Networked Multimedia Systems Video Basics Image and Video Lossless Compression. Leif Arne Rønningen Autumn 2008. Graphics and Image Data Representations. Large number of (file) formats, PDF, JPEG, GIF, PNG, BMP 8 bit Gray-Level Images 24 bit Color Images, RGB

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TTM4142 Networked Multimedia Systems Video Basics Image and Video Lossless Compression

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  1. TTM4142 Networked Multimedia SystemsVideo BasicsImage and VideoLossless Compression Leif Arne Rønningen Autumn 2008

  2. Graphics and Image Data Representations • Large number of (file) formats, PDF, JPEG, GIF, PNG, BMP • 8 bit Gray-Level Images • 24 bit Color Images, RGB • Color Lookup Table - LUT • Dithering

  3. Color in Image and VideoSpectral power distribution of daylight Wavelength (nm)

  4. Human Vision

  5. CIE tristimulus values

  6. Color Models in VideoYUV – PAL and CCIR 601 digital videoYCrCb – JPEG, MPEG, ITU-R 601-4

  7. Fundamental Video Concepts • Component Video, RGB, YUV, YCrCb • Composite Video, chrominance and luminance signals on single carrier • S-Video, separated video, one wire for luminance, one wire for composite chrominance • Analog Video, PAL, interlaced scan, blanking intervals h, v • Digital Video, YCrCb - chroma subsampling

  8. Digital Video

  9. HDTV H.264, (MPEG-4 part 10)

  10. Lossless Compression AlgorithmsInformation theory Alphabet S = Entropy

  11. Run-length Coding The string AABACCCCCCCCCCDEAB can be coded as !02ABA!10CDEAB Which is 14 instead of 18 characters ! Must be reserved

  12. LZW Compression With this algorithm, the encoder and decoder build up the same dictionary of recognized strings from a stream dynamically. Each string is given a codeword. The encoder sends short codewords instead of long strings. See Li and Drew for details

  13. Arithmetic Coding, Sequence to be coded: CAEE$

  14. Arithmetic Coding

  15. Arithmetic Coding, Decoding • The coded sequence CAEE$ ends up with the interval [0.33184, 0.3322) • Find the shortest binary number that is within this interval, 0.01010101 <=> 0.33203125 (procedure 7.2 in book) • Note that only 8 bits is needed! • For decoding, go the opposite way of that in the previous slide • 0.33203125 is in Low-High interval for C • (0.33203125-0.3)/0.2 = 0.16015624, an A • and so on

  16. Comparing some lossless compression schemes

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