1 ttm4142 networked multimedia systems video basics image and video lossless compression leif arne...
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TTM4142 Networked Multimedia Systems
Video BasicsImage and Video
Lossless Compression
Leif Arne Rønningen
Autumn 2008
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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
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Color in Image and Video
Spectral power distribution of daylight
Wavelength (nm)
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Human Vision
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CIE tristimulus values
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Color Models in VideoYUV – PAL and CCIR 601 digital videoYCrCb – JPEG, MPEG, ITU-R 601-4
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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
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Digital Video
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HDTV
H.264, (MPEG-4 part 10)
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Lossless Compression AlgorithmsInformation theoryAlphabet S =
Entropy
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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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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
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Arithmetic Coding, Sequence to be coded: CAEE$
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Arithmetic Coding
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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
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Comparing some lossless compression schemes