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多媒體網路安全實驗室
Reversible Data Hiding By Using
Modified Difference Expansion
Source: Signal Processing Systems (ICSPS) , 2010 2nd International
Conference
Authors: Masoumeh Khodaei, Karim Faez
Speaker:Cheng Hsu
Date:2010/12/01
多媒體網路安全實驗室
Outline
1. Introduction
2. Related works
3. Proposed method
4. Experimental results
5. Conclusions
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1.Introduction
They propose a reversible data hiding
method with low time complexity and
high embedding capacity for gray-scale
images.
This method presents a block-based
lossless data hiding schema to utilize
the similarity between neighborhood
pixels in the block to improve the
marked-image quality.
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2.Related works
Tian’s method
Embedding phase
 Pi  Pj 
m
 , d  Pi  Pj
 2 
d '  2 d  s
'
'




d

1
d
'
'
( Pi , Pj )  (m  
 , m   )
 2 
2
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Average value m
Difference value d
Secret data bit s
多媒體網路安全實驗室
Extracting phase
d '  Pi ' Pj '
s  d ' mod 2
 Pi ' Pj ' 
 d '
m'  
,d   
2
 2 
 d  1
d 
( Pi , Pj )  (m' 
, m'   )

 2 
2
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Example
Embedding phase
( Pi , Pj )  (206,201)
 206  201
m
 203, d  206  201  5

2


secret data bit s  12
d '  2  5  1  11
11  1
11
( Pi ' , Pj ' )  (203  
,203    )  (209,198)

 2 
2
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Extracting phase
( Pi ' , Pj ' )  (209,198)
d '  209  198  11
secret data bit s  11 mod 2  1
11
 209  198 
 203, d     5
m'  

2
2


5
 5  1
,203    )  (206,201)
( Pi , Pj )  (203  

2
 2 
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3.Proposed method
Embedding phase
1.Find the central-pixel bc of each block.
n n
bc  B (  ,   )
2 2
2.Compute the difference value di .
di  bi  bc
3. Embed the secret data bit s into each difference
value and obtain new difference value di’ .
di '  (di  2)  s
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4. Calculate the new pixel value bi’ for all of
pixels in the block.
bc  di ' , if bi  bc
bi '  
bc  di ' , if bi  bc
5. Replace the new block into host image.
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Extracting and Recovery Phase
1.Compute the difference value di’.
di '  bi 'bc
2.Extract the secret data bit s from each
difference value.
s  di ' mod 2
3. Calculate the original pixel value bi for all of
pixels in the block. b   d i ' , if b '  b
i
c
 c 2

 
bi  
b   d i ' , if b '  b
i
c
 c  2 
多媒體網路安全實驗室
Example Embedding phase
1. bc
d1  93  100  7, d 5  101  100  1
99
2. di
d 2  98  100  2, d 6  102  100  2
93
98
97
100 101
d 3  99  100  1, d 7  104  100  4
102 104 103
d 4  97  100  3, d 8  103  100  3
S=(11011001)2
d1'  (7  2)  1  15, d 5'  (1  2)  1  3
3. di’
d 2'  (2  2)  1  5, d 6'  (2  2)  0  4
d 3'  (1  2)  0  2, d 7'  (4  2)  0  8
d 4'  (3  2)  1  7, d 8'  (3  2)  1  7
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多媒體網路安全實驗室
b1'  bc  d1'  100  15  85, b5'  bc  d 5'  100  3  103
4. bi’
b2'  bc  d 2'  100  5  95, b6'  bc  d 6'  100  4  104
b3'  bc  d 3'  100  2  98, b7'  bc  d 7'  100  8  108
b4'  bc  d 4'  100  7  93, b8'  bc  d8'  100  7  107
93
98
99
85
95
97
100 101
93
100 103
102 104 103
98
104 108 107
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Example Extracting and Recovery
Phase
1. The difference value of pixels between bc
and bi .
d1 '  85  100  15, d 5 '  103  100  3
85
95
98
93
100 103
104 108 107
d 2 '  95  100  5, d 6 '  104  100  4
d 3 '  98  100  2, d 7 '  108  100  8
d 4 '  93  100  7, d8 '  107  100  7
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2. Extract the secret data bit s
s1  d1' mod 2  15 mod 2  1
s2  d 2' mod 2  5 mod 2  1
s3  d 3' mod 2  2 mod 2  0
s4  d 4' mod 2  7 mod 2  1
s5  d 5' mod 2  3 mod 2  1
s6  d 6' mod 2  4 mod 2  0
s7  d 7' mod 2  8 mod 2  0
s8  d 8' mod 2  7 mod 2  1
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3. The original values of pixels in the block
can be obtained.
93
98
99
97
100 101
102 104 103
15 
3
b1  100     93, b5  100     101
2
2
5
4
b2  100     98, b6  100     102
2
2
2
8
b3  100     99, b7  100     104
2
2
7
7
b4  100     97, b8  100     103
2
2
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多媒體網路安全實驗室
4.Experimental results
(a) 2×2 blocks (b) 3×3 blocks (c) 4×4 blocks (d) 5×5 blocks
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PSNR
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Embedding capacity of proposed method for Lena image
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Hiding capacity
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5.Conclusions
The experimental results of their proposed
method showed that the quality of markedimage is high and is close to Lee et al.'s
method.
The hiding capacity of their proposed
method is very higher than Tian's method
while the PSNR values of their method are
maintained acceptable.
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