Still Image Conpression JPEG & JPEG2000

Still Image ConpressionJPEG & JPEG2000Yu-Wei Chang

2003 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 probability of coeff

Transform Quantization EntropyCoding

Image data

Outputdata

equal important

High-> low High-> low0101010……

JPEG

JPEG Joint Photographic Expert Group A generally used lossy image coding format Allow tradeoff between compression ratio and image quality Can achieve high compression ratio(20+) with almost invisible difference

JPEG Coding/Decoding Flow

DCT Quantizer DataEntropy Coder

Coding TableQuantization

TableTables

DataTables

Entropy DecoderInverse

Quantizer IDCT

Coding TableQuantization

Table

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 Quantization EntropyCoding

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.