Unequal Protection of JPEG2000 Code-Streams in Wireless Channels

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
• 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.

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 (ICIP02).

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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.

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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.

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Error Resilience in JPEG2000

• Code-Blocks,Precincts and Packets

HL2
embedded code-block bit-streams
LL2
HL1
HH2
LH2
Packets
HH1
LH1
Precinct in the next lowest resolution
Precinct in the highest resolution
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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.

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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

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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.

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Impact of Existing Error Resilience Tools
Concealment Resync
No. of layers1, Precinct Size 256,128,64
No Concealment Resync
No Concealment No Resync
No. of layers6, Precinct Size 256,128,64
No of Layers1, Single Precinct
No of Layers6, Single Precinct

• Resync Markers and Error Concealment are very
  useful tools
• Multiple quality layers of little benefit when
  multiple precincts are employed.

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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
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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.

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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
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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.

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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
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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.

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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.