1. Unequal Protection of JPEG2000 Code-Streams in Wireless Channels
Ambarish Natu & David Taubman
School of Electrical Engineering & Telecommunications
The University of New South Wales, Australia

2. Introduction JPEG2000 suited for Wireless Image Transmission Objective
Better quality at lower bit rates compared to its predecessors.
Error Resilience tools provided within the standard.
Option to include RESYNC Markers
Error concealment and error localizing tools.
Partition compressed data into independently decodable elements.
Objective
Development of unequal error protection schemes for JPEG2000 compressed imagery.
Optimize JPEG2000 coding parameters.
Maximize image quality in the presence of random bit errors.
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

3. Previous Work
Hamming Codes used to provide unequal error protection to JPEG2000 code-stream (1999)
Turbo codes also proposed. (2000 & 2002)
Both approaches do not consider the problem of optimizing JPEG2000 coding parameters.
Do not consider application of different levels of protection to different quality layers in the code-stream.
RCPC codes proposed by Z.Wu, A.Bilgin & M.Marcellin (ICIP’02).
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

4. Wireless Channels Wireless Models
Bit Level
Each bit may be corrupted.
Packet Level
Data is partitioned into packets
Each packet received or lost
We restrict our work to bit level errors, assuming a memoryless error process.
Characterized only by BER.
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

5. Reed-Solomon (RS) Codes
RS codes over Galois Field GF( ) are of particular interest to us.
For the present study we work with GF(16).
Each symbol is a nibble
Investigate the use of (15,7), (15,9), (15,11) and (15,13) RS Codes
Simpler to decode than turbo or convolutional codes
Loss of multiple consecutive bits ( ) is rarely worse than loss of single bit in J2K.
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

6. Error Resilience in JPEG2000
Code-Blocks,Precincts and Packets:
HL2
embedded code-block bit-streams
LL2
HL1
HH2
LH2
Packets
LH1
HH1
Precinct in the next lowest resolution
Precinct in the highest resolution
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

7. Error Resilience in JPEG2000 (ctd.)
JPEG2000 Packets (not network packets)
Each packet consists of a packet head and a packet body
Incremental contributions from code-block bit-streams belonging to the relevant precinct.
To extract code-block bit-stream contributions from packet body
Must correctly decode the header of that packet and all preceding packets from the same precinct.
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

8. Error Resilience in JPEG2000 (ctd.)
Quality Layer Contribution
Layers
The first layer is a collection of all first packets from each precinct in the image. The second layer consists of the second packet from each precinct and so forth.
Effect of Layering
Layer bit-rates may be set by J2K compressor
More smaller layers.
More packets per precinct.
Less information in each packet header
Less likely to lose whole precinct if corrupted.
More significantly, can assign different levels of protection to layers
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

9. Error Resilience in JPEG2000 (ctd.)
Error Concealment
ERTERM
Decoder can exploit predictable termination to detect and conceal errors in code-block bit-streams.
Additional ER Tools
SEGMARK
Four-symbol code inserted immediately before the first new coding pass in each magnitude bit-plane.
If an error occurs in the preceding 3 coding passes there is 1 in 16 chance that it will go undetected.
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

10. Impact of Existing Error Resilience Tools
Concealment & Resync
No. of layers=1, Precinct Size
{256,128,64}
No Concealment & Resync
No Concealment & No Resync
No. of layers=6, Precinct Size
{256,128,64}
No of Layers=1, Single Precinct
No of Layers=6, Single Precinct
Resync Markers and Error Concealment are very useful tools
Multiple quality layers of little benefit when multiple precincts are employed.
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

11. Uniform Error Protection
Almost 9 dB improvement in image quality with (15,9) code at both BER compared to the existing ER tools
4 dB loss in image quality under noiseless condition for (15,9) code
Disadvantage:
All elements protected equally
(15,9) code
(15,13) code
Existing error resilience tools
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

12. Unequal Error Protection
Code-stream organized into 6 quality layers with cumulative bit-rates of , , 0.125, 0.25, 0.5 and 1.0 bits per sample
Error sensitivity increases from lower to higher quality layers.
Key factor is spacing between layers
2 layers for each factor of 2 change in cumulative bit-rate i.e.11 layers in all.
Finer layer spacing gives little further improvement.
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

13. Unequal Error Protection (ctd.)
Scheme-A
2 layers for each factor of
two changes in bit-rate
Scheme-B
Uniform FEC
(15,9) code
Scheme-A: Layer (0,1 & 2) protected with (15,9) code
Layer (3 & 4) protected with (15,11) code
Layer (5) protected with (15,13) code.
Scheme-B: Layer (0) protected with (15,7) code
Layer (1,2 & 3) protected with (15,9) code
Layer (4 & 5 ) protected with (15,11) code
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

14. Result Interpretation
Unequal Protection across quality layers is of significant benefit
Improvement in noiseless compression performance
Strongest codes used to protect only initial quality layers , which contain many fewer data bytes than later layers.
Simple codes robust to BER conditions.
Little impact on error-free conditions.
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

15. Unprotected Vs Protected JPEG200 Code-stream
a) PSNR: dB
BER:
b) PSNR: dB
BER:
Unprotected JPEG2000 code-stream (using only existing ER tools) for BER of
and
c) PSNR: dB
BER:
d) PSNR: dB
BER:
Protected JPEG2000 code-stream (using (15,9) RS code) for BER of
and
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

16. Other Questions
Precincts are of significant benefit when FEC codes are not used to protect JPEG2000 code-stream.
Interestingly, multiple precincts do not help when combined with equal or unequal error protection.
Additional cost for independently coding each packet header and aligning packet on a whole codeword boundary.
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan

17. Summary
Resync markers, error concealment, layering & precincts improve error resilience when FEC codes are not used to protect JPEG2000 code-stream.
Layering largely irrelevant unless unequal error protection employed.
Unequal Protection of quality layers definitely beneficial
Use Octave bit-rate spacing.
2 layers per octave offer some help at lower bit error rates.
Multiple precincts of little benefit when RS codes are used to protect compressed data.
Natu, Taubman
UNSW
GLOBECOM’02, November 17-21
Taipei, Taiwan