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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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多媒體網路安全實驗室
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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多媒體網路安全實驗室
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
4
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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多媒體網路安全實驗室
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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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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