still image conpression jpeg & jpeg2000 yu-wei chang 2003 4/18
TRANSCRIPT
Still Image ConpressionJPEG & JPEG2000
Yu-Wei Chang2003 4/18
Outline
Image Compression Background Overview of JPEG Overview of JPEG2000 Comparsion
Why Image Conpression Why?
Bandwidth Storage
How Remove redundancy
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……
JPEG
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
JPEG Coding/Decoding Flow
DCT Quantizer DataEntropy Coder
Coding TableQuantization
TableTables
DataTables
Entropy DecoderInverse
Quantizer IDCT
Coding Table
QuantizationTable
JPEG-2000
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)
JPEG2000 v.s. JPEG
low bit-rate performance
JPEG2K - Quality Scalability
Improve decoding quality as receiving more bits:
Spatial Scalability
Multi-resolution decoding from one bit-stream:
ROI (range of interest)
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
Discrete Wavelet Transform
LL2 HL2
LH2 HH2HL1
LH1 HH1
JPEG v.s. JPEG-2000
JPEG2000 v.s. JPEG
Transform QuantizationEntropyCoding
JPEG
J2K
DCT DiscreteCosineTransform
DWT DiscreteWaveletTransform
8x8Quantization
Table
Quantizationfor each
sub-band
HuffmanCoding
ArithmeticCoding
Conclusion
JPEG2000 provides more functionality, and higher compression performance at low bit-rate
However, higher complexity, and more memory requirement.