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

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

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

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

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

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

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

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

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

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

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

Unequal Error Protection Code-stream organized into 6 quality layers with cumulative bit-rates of 0.03125, 0.0625, 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

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

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

Unprotected Vs Protected JPEG200 Code-stream a) PSNR: 17.64 dB BER: b) PSNR: 23.50 dB BER: Unprotected JPEG2000 code-stream (using only existing ER tools) for BER of and c) PSNR: 26.24 dB BER: d) PSNR: 34.34 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

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

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