Compression: Why? Shannon! H = ²log S^n = n log S H: information S: number of symbols n: messagelength But what if we know what to expect? 2, n = 4 has same info content as S = 16, n = 1 e 4 log 2 = 1 log 16 can e.g. code 4 bits as one hexadecimal number Entropy: m: a possible message p: probability H = -Σ p(m) ²log p(m) 4 random bits (16 r. messages): H = - 16 * 1/16 ²log 1/16 = 4 bit
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Compression: Why? Shannon!
H = ²log S^n = n log S
H: informationS: number of symbolsn: messagelength
But what if we know what to expect?So S = 2, n = 4 has same info content as S = 16, n = 1Because 4 log 2 = 1 log 16So we can e.g. code 4 bits as one hexadecimal number
Entropy:m: a possible messagep: probability
H = -Σ p(m) ²log p(m)
4 random bits (16 r. messages):H = - 16 * 1/16 ²log 1/16 = 4 bit
Blockwise Fourier: blocking artefact
Quantisation artefact
Vector quantisation
Inter-frame compression artefacts
Segmentation: Use most bandwith for important parts
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