1

A High-Capacity Steganography Scheme for

JPEG2000 Baseline System

Liang Zhang, Haili Wang, and Renbiao Wu,

Senior Member, IEEE

1

IEEE TRANSACTIONS ON IMAGE PROCESSING, VOL. 18, NO. 8, AUGUST 2009Received September 09, 2008; revised April 01, 2009.

First published April 24, 2009; current version published July 10, 2009.

Adviser: Chih-Hung Lin

Speaker:Po-Kai Shen

Date : 98/11/24

22

Outline

1. Author

2. Introduction

3. Jpeg2000 baseline coding system

4. Steganography based on twice bit-plane encoding

5. Redundancy evaluation

6. Synchronization information and scrambling measure

7. Simulation

8. Conclusion

33

Author(1)

Liang Zhang was born in 1970. He received the Ph.D. degree in electronic information engineering from Tianjin University, Tianjin, China, in 2003.

He is an Associate Professor. He is currently with the Tianjin Key Lab of Advanced Signal Processing in Civil Aviation University of China.

His current research interests include image processing, information hiding, and intelligent visual surveillance.

44

Author(2)

Haili Wang was born in 1983.

She is now a postgraduate specializing in signal processing.

Her current research interests include image processing and information hiding.

55

Author(3)

Renbiao Wu (M’95–SM’01) received the B.Sc. And M.Sc. degrees from Northwestern Polytechnic University, Xian, China, in 1988 and 1991, respectively, and the Ph.D. degree from Xidian University, Xian,in 1994, all in electrical engineering.

From May 1994 to February 1996, he was a Postdoctoral Fellow at the College of Marine Engineering, Northwestern Polytechnic University, where he was promoted to Associate Professor in December 1995.

From March 1996 to February 1997, he was a Visiting Scholar at the Center for Transportation Research, Virginia Polytechnic Institute and State University,Blacksburg.

66

From March 1997 to December 1998, he was a Visiting Scholar at the Department of Electrical and Computer Engineering, University of Florida,Gainesville.

Since January 1999, he has been with the Tianjin Key Lab for Advanced Signal Processing, Civil Aviation University of China, Tianjin, China, where he is currently a Chaired Professor and director of the lab.

Author(3)

77

From August 2004 to January 2005, he was a Distinguished Research Scholar in the Department of Electrical and Electronic Engineering, Imperial College London, London, U.K. Dr. Wu was the recipient of the National Outstanding Young Investigator Award of China in 2003.

His research interests include space-time adaptive processing, adaptive arrays, feature extraction and image formation, spectral estimation and their applications to radar and wireless communication systems.

Author(3)

88

Introduction

1) Modern information hiding technology is an

important branch of information security.

2) Steganography

three competing aspects :

① Capacity

② Security

③ Robustness

99

Introduction

3) Section III shows procedures of JPEG2000 baseline

system and points out the problem due to bitstream

truncation.

4) Section IV describes the principle of twice bit-plane

encoding and illustrates the operation procedures.

5) Section V gives a detailed description on redundancy

evaluation, and explains how embedding points and their

intensity are adjusted.

1010

Introduction

6) Section VI, we define measures for synchronization and

security.

7) Section VII shows the simulation results.

8) Section VIII draws a conclusion.

11

Jpeg2000 baseline coding system

JPEG2000 uses uniform scalar quantizers with enlarged

“deadzones.”

Truncating the embedded bitstream associated with any

given codeblock has the effect of quantizing the wavelet

coefficients in that codeblock more coarsely.

That is to say, there still exists a lossy procedure after

entropy encoding.

1212

Steganography based on twice bit-plane encoding

1313

Steganography based on twice bit-plane encoding

1) There are three sub-steps involved in the determination of

embedding points and embedding intensity for a code block.

2) Scrambled synchronization information and secret

messages are embedded into the selected embedding

points from the lowest embed-allowed bit-plane to higher

ones.

3) Secondary bit-plane encoding is operated after information

embedding.

1414

Steganography based on twice bit-plane encoding

Ensured at the cost of increased computational complexity

and slightly changed compression ratio.

1515

Redundancy evaluation

Where is the quantized wavelet coefficient with the bits

lowerthan the highest no-zero bit are replaced by zeros.

The parameter is the quantization step of the wavelet

coefficient . The parameter assumes a value between

0 and 1. According to , a typical value of is 0.7. The result

of the first step is denoted as

ix

i

ix

iy

(1)

1616

Redundancy evaluation

In the second step, the neighborhood masking effect is

exploited to process the wavelet coefficients as the following:

(2) The neighborhood contains wavelet coefficients within a

window of N by N, centered at the current position.

The parameter is the total number of wavelet coefficients

in the neighborhood.

(2)

i

1717

Redundancy evaluation

The parameter assumes a value between 0 and 1,

together with , is used to control the strength of

embedding intensity adjustment due to neighborhood

masking.

The symbol denotes the neighboring wavelet coefficients

greater than or equal to 16, and all its bits lower than the

highest no-zero bit are set to be zeros.

(2)

i

kx̂

1818

Redundancy evaluation

(3)

(4) In the third step, a weighting factor about brightness

sensitivity is used in the processing.

The symbol denotes the subband at resolution level

.and with orientation .

The symbol denotes the wavelet coefficient

located at in subband .

The levels of discrete wavelet decomposition is k.

lI

kl ...1,0 HHHLLHLL ,,,

jiI l ,

ji, lI

1919

Redundancy evaluation

The pixel value has a dynamic range of [ -128, 127]. The local

average brightness is normalized by dividing 128. Then the

result of the third step, , is given byiz

(5)

Quantization redundancy is calculated by the following equation:

(6)

The redundancy of the wavelet coefficient can be

measured by .irix

2020

Redundancy evaluation

Use the wavelet coefficients with not less than 2 to carry

message bits.

The rule of adjustment on embedding points and intensity is

as follows:

ir

1) If , then this candidate embedding point should

be removed.

2) If , then the embedding capacity of this

point is determined to be n bits.

2ir

122 ni

n r

2121

Synchronization information and scrambling measure

The first part of the synchronization information is a 2-bit flag

that indicates whether a certain code block contains secret

message.

The second part of the synchronization information is a 12-bit

fragment that indicates the length of the secret message

embedded in this code block.

2222

Synchronization information and scrambling measure

The third part of the synchronization information is a 12-bit

fragment that indicates the length of the secret message

embedded in this code block.

2323

Synchronization information and scrambling measure

A 64-bit secret key is used as a seed to generate a

sequence of pseudo random binary numbers, which is used

to scramble the message bits.

N is the total number of message bits.

The symbol denotes the message bit, and the

binary number of the pseudo random sequence. The

operator ⊕ denotes binary addition. The scrambled

message bits, denoted as , are to be embedded into

selected wavelet coefficients.

is

im in

is

thithi

2424

Simulation

Fig. 6.

(a)Original image used as cover media.

(b)the binary logo image used as secret message.

2525

Simulation

In the first step, the lowest embed-allowed bit-plane of each

code block is determined.

In the second step, the wavelet coefficients with magnitudes

not less than a given threshold are chosen as candidate

embedding points.

In the third step, the candidate embedding points are

adjusted image adaptively based on redundancy evaluation

to increase hiding capacity

In the fourth step, we embed message bits into the selected

wavelet coefficients and finish encoding the stego-image

2626

Simulation

The threshold is set to 16

The parameters in those equations are set to be: N=5 ,

α=0.7 , β=0.2

Evaluation results for wavelet coefficients A, B, and D are as

follows: 72.1Ar 59.2Br 4.13Cr

2727

Simulation

21 259.22 43 24.132

1) If , then this candidate embedding point should

be removed.

2) If , then the embedding capacity of this

point is determined to be n bits.

2ir

122 ni

n r

B:

D:

2828

Simulation

Experiment shows that information hiding has caused slight

change on PSNR (Peak Signal to Noise Ratio) and the

actual compression ratio.

2929

Simulation

In order to test and measure the effectiveness on hiding

capacity enlargement, we simply bypass the redundancy

evaluation for comparison. Two methods are tested in the

experiments.

Method 1: With redundancy evaluation.

Method 2: Without redundancy evaluation.

3030

Simulation

Fig. 10.

(a) Crown

(b) Baboon

TABLE IHIDING CAPACITY OF THE THREE TEST IMAGES

（ A compression ratio of 0.8 bits per pixel）

3131

Simulation

Fig. 11. Hiding capacity of different compression ratios.

3232

Simulation

Fig. 12. Four images in the database

3333

Simulation

Fig. 13. ROC curves tested on different payloads.

3434

Simulation

The detector does work only if the message length greatly

exceeds the hiding capacity.

The proposed steganography scheme can be considered

undetectable in the situation of lower payloads than hiding

capacity.

3535

Conclusion

The contributions of this work are mainly focused on

dealing with two problems: bitstream truncation and

redundancy measurement.

3636

備註（ 1）