Unequal Protection of JPEG2000 Unequal Protection of JPEG2000 Code-Streams in Wireless ChannelsCode-Streams in Wireless Channels

Ambarish Natu & David Taubman

School of Electrical Engineering & Telecommunications

The University of New South Wales, Australia

Natu, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

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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.

Natu, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

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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, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

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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.

Natu, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

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• 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.

m2

Reed-Solomon (RS) Codes

km

Natu, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

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Error Resilience in JPEG2000

• Code-Blocks,Precincts and Packets:

LLLL22

LHLH22HHHH22

HLHL22

HLHL11

HHHH11LHLH11

Precinct in the highest resolution

embedded code-block bit-streams

Packets

Precinct in the next lowest resolution

Natu, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

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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.

Natu, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, 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, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, 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, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

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Impact of Existing Error Resilience Tools

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

Resync Markers & Error Concealment

0

5

10

15

20

25

30

35

40

45

0 0.0001 0.001

BER

PS

NR

(dB

)

Precinct Sizes and Number of Layers

15

20

25

30

35

40

0 0.0001 0.001

BER

PSNR

(dB)

Concealment & Resync

No Concealment & Resync

No Concealment & No Resync

No of Layers=1, Single Precinct

No. of layers=1, Precinct Size

{256,128,64}

No. of layers=6, Precinct Size

{256,128,64}

No of Layers=6, Single Precinct

Natu, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

11

Uniform Error Protection

15

20

25

30

35

40

0 0.0001 0.001

BER

PS

NR

(d

B)

• 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, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

12

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, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

13

Unequal Error Protection (ctd.)

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

26

28

30

32

34

36

38

0 0.0001 0.001

BER

PS

NR

(d

B)

Scheme-A

Scheme-B

Uniform FEC

(15,9) code

2 layers for each factor of

two changes in bit-rate

Natu, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, 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, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

15

Unprotected Vs Protected JPEG200 Code-stream

Unprotected JPEG2000 code-stream (using only existing ER tools) for BER of

Protected JPEG2000 code-stream (using (15,9) RS code) for BER of

a) PSNR: 17.64 dB

BER:

c) PSNR: 26.24 dB

BER:

b) PSNR: 23.50 dB

BER:

d) PSNR: 34.34 dB

BER:

410

410

310

310

410 310and

and 310

Natu, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, Taiwan

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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.

Natu, TaubmanUNSW

GLOBECOM’02, November 17-21Taipei, 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.