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.