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Still Image ConpressionJPEG & JPEG2000
Yu-Wei Chang2003 4/18
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Outline
Image Compression Background Overview of JPEG Overview of JPEG2000 Comparsion
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Why Image Conpression Why?
Bandwidth Storage
How Remove redundancy
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Still Image Coding Flow Most still image coding flow are similar
Transform: translate image to freq domain Quantization: reduce unimportant data Entropy coding: encode data according to prob
ability of coeff
Transform QuantizationEntropyCoding
Image
data
Output
data
equal important
High-> low High-> low
0101010……
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JPEG
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JPEG Joint Photographic Expert Group A generally used lossy image coding f
ormat Allow tradeoff between compression r
atio and image quality Can achieve high compression ratio(2
0+) with almost invisible difference
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JPEG Coding/Decoding Flow
DCT Quantizer DataEntropy Coder
Coding TableQuantization
TableTables
DataTables
Entropy DecoderInverse
Quantizer IDCT
Coding Table
QuantizationTable
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JPEG-2000
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JPEG 2000 Features
Not only better efficiency, but also more functionality
Superior low bit-rate performance Lossless and lossy compression Multiple resolution Range of interest(ROI)
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JPEG2000 v.s. JPEG
low bit-rate performance
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JPEG2K - Quality Scalability
Improve decoding quality as receiving more bits:
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Spatial Scalability
Multi-resolution decoding from one bit-stream:
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ROI (range of interest)
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JPEG2000 EncoderBlock Diagram
Key Technologies: Discrete Wavelet Transform (DWT) Embedded Block Coding with
Optimized Truncation (EBCOT)
QuantizationEBCOT Tier-1
Encoder(CF + AE)
EBCOTTier-2
Encoder
Rate Control
2-D DiscreteWavelet
Transform
transform quantize coding
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Discrete Wavelet Transform
LL2 HL2
LH2 HH2HL1
LH1 HH1
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JPEG v.s. JPEG-2000
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JPEG2000 v.s. JPEG
Transform QuantizationEntropyCoding
JPEG
J2K
DCT DiscreteCosineTransform
DWT DiscreteWaveletTransform
8x8Quantization
Table
Quantizationfor each
sub-band
HuffmanCoding
ArithmeticCoding
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Conclusion
JPEG2000 provides more functionality, and higher compression performance at low bit-rate
However, higher complexity, and more memory requirement.