1 TTM4142 Networked Multimedia Systems Video Basics Image and Video Lossless 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 Video Spectral power distribution of daylight Wavelength (nm)

4 Human Vision

5 CIE tristimulus values

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7 Color Models in Video YUV – PAL and CCIR 601 digital video YCrCb – JPEG, MPEG, ITU-R 601-4

8 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

9 Digital Video

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

11 Lossless Compression Algorithms Information theory Alphabet S = Entropy

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

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15 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

16 Arithmetic Coding, Sequence to be coded: CAEE$

17 Arithmetic Coding

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

19 Comparing some lossless compression schemes