Understanding JPEG and JPEG2000 Image Compression Standards

1. JPEG JPEG2000 JPEG - JPEG2000 Isabelle Marque Let's go Jackets!

2. JPEG • Joint Photographic Experts Group • Committe created in 1986 by: International Organization for Standardization (ISO) and International Telecommunication Union (ITU) • A working group which creates the standard for still image compression

3. JPEG - JPEG2000 • Two different standards • Major differences : JPEG JPEG2000 Created for natural imagery Discrete Cosine Transformalgorithm Created for computer generated imagery Discrete Wavelet Transform algorithm

4. Source image data Forward transform Entropy encoding Compressed image data Quantization JPEG • Architecture of standard • Forward transform • Quantization • Entropy coding • DC coefficient • AC coefficients

5. Source image data Forward transform Entropy encoding Compressed image data Quantization JPEG • Forward transform • Level shifted • Divided into blocks of 8*8 pixels • Forward DCT:

6. JPEG • DCT basis functions

7. JPEG • Original image

8. JPEG • DCT coefficients

9. Source image data Forward transform Entropy encoding Compressed image data Quantization JPEG • Quantization • Quantization table • Zigzag scan

10. JPEG • Quantization table

11. JPEG • Labels after quantization

12. Source image data Forward transform Entropy encoding Compressed image data Quantization JPEG • Entropy encoding • DC coefficient and AC coefficients are coded differently • DC coefficient • Encode the difference • Huffman code unmanageable • First bits to define the category and other bits to define the element in the category

13. JPEG • AC coefficients Defined by a certain number of terms: • Category C that a non zero label falls in • Z: number of zero since the last non zero label • Z/C points to a specific code • Follows by bits to define the element in the category • +1 code • EOB stands for End Of Block: A code after the last non zero value

14. JPEG • Sample table for obtaining the huffman code

15. JPEG • Reconstructed image

16. JPEG • More accurate image • Increase the bit rate • Decrease quantization table elements • Less accurate image • Decrease the bit rate • Increase quantization table elements • Problem: Low rate image: « blockiness »

17. JPEG2000 • Can be both lossless and lossy • Improves image quality • Uses a layered file structure : • Progressive transmission • Progressive rendering • File structure flexibility: • Could use for a variety of applications • Many functionalities

18. Source image data Forward transform Entropy encoding Compressed image data Quantization JPEG2000 • Architecture of standard • Forward transform • Quantization • Entropy coding

19. Source image data Forward transform Entropy encoding Compressed image data Quantization JPEG2000 • Forward transform • Level shifted • Divided into blocks • Forward Discrete Wavelet Transform

20. JPEG2000 • Details

21. JPEG2000

22. JPEG2000 • Discrete Wavelet Transform can be : • Irreversible: Daubechies 9-tap/7-tap filter • Reversible: 5-tap/3-tap filter • Any user could supply wavelet filter banks

23. Source image data Forward transform Entropy encoding Compressed image data Quantization JPEG2000 • Quantization Dynamic range: depends on the number of bits and the choice of the wavelet Exponent Mantissa

24. Source image data Forward transform Entropy encoding Compressed image data Quantization JPEG2000 • Entropy encoding • Embedded Block Coding with Optimization Truncation of the embedded bit stream (EBCOT) • Each subband is divided into rectangular blocks which are coded independently called code blocks • Bitstream is organized in a succession of layers • Each layer corresponds to a certain distortion level • The quality of the reproduction is proportional to the numbers layers received

25. JPEG2000 • Layered structure

26. JPEG JPEG2000 JPEG - JPEG2000 - Quality • At compression ratio: 43:1

27. JPEG - JPEG2000 - Quality • Method of picture quality measurement:PSNR Peak Signal To Noise Ratio in dB: Pixel of the image Pixel of the reconstructed image Size of the image Root Mean Squared Error

28. JPEG - JPEG2000 - Quality • Comparison of PSNR values (dB) compressed colour images

29. CONCLUSION – Key points • JPEG: DCT algorithm • JPEG2000: DWT algorithm • Layered structure • Many functionalities • For a similar quality of PSNR, JPEG2000 compresses almost twice more than JPEG

30. REFERENCES • Introduction to Data Compression, K. Sayood, Morgan Kauffman, Second Edition, 2000. (Primary) • A.N. Skodra, C.A. Christopoulos, T. Ebrahimi, « JPEG2000, the upcoming still image compression standard », Proceeding of the 11th Portuguese Conference on Pattern recognition, Porto, Portugal, May 11th-12th, pp. 359-366, 2000 • JPEG, Official site: http://www.jpeg.org • Home page of a member: http://www.etro.vub.ac.be/members/christopoulos.charilaos/welcome.html • http://www.aware.com/products/compression/j2kmaindemo.html • http://www.cs.sfu.ca/CC/820/li/material/presentations/paper21.ppt • http://dmsun4.bath.ac.uk/research/sar/dwt.html • http://www.us.design-reuse.com/articles/article6691.html • PSNR:http://www.snellwilcox.com/knowledgecenter/whitepapers/papers/picturequality_mpeg2.pdf • Quality: http://jj2000.epfl.ch/jj_publications/papers/001.pdf

31. QUESTIONS?