Pattern Recognition Letters 25 (2004) 1431–1437
Chin-Chen Chang *, Hsien-Wen Tseng
Speaker:王軍証 2009/03/17
1
1.
2.
3.
4.
Introduction
The proposed method
Experimental results and discussions
Conclusions
2


In this paper, we propose a novel
steganographic method to hide data in spatial
domain of images imperceptibly.
This method does not replace the LSBs of
pixel value directly, but changes the pixel
value into another similar value.
3
1)
2)
3)
Two-sided side match steganography
Three-sided side match steganography
Four-sided side match steganography
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
1.
Given an input pixel PX with gray
value g x , let g u and gl be the
gray values of its upper PU pixel
and left PL pixel, respectively.
A difference value d is computed as
d  ( gu  gl ) / 2  g x
(1)
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2.
3.
If d has values -1, 0, or 1, then one bit
secret data is embedded into the LSB of
pixel PX. Otherwise, the number embedded
of bits, say n , is calculated by
n  log 2 d , if d  1
(2)
A new difference d  which is converted to
integer b is computed as
2n  b,
d  
n

2
b ,



if d  1
if d  1
(3)
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4.
The new value of the pixel PX is defined to
be
g x  gu  gl /2  d 
(4)
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

EX: The gray value of the given pixel PX is
assumed to be 47. The two neighboring
pixels have values 40 and 82.
d  (40  82) / 2  47  14
n  log 2 d  3
b  1012  5
d   23  5  13
g x  (40  82) / 2  13  48
The extraction of embedding data is
d   (40  82)  48  13
b  13 mod 23  5
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Sometimes, the new value of pixel PX may fall
off the boundary of the range [0,255] in the
fol in the following cases:
n 1
(
g

g
)
/
2

2
 1 .From Eq. (4),
d

1
1.
and u
l
g x  gu  gl  / 2  d   gu  gl  / 2  (2n  b)

 gu  gl  / 2  (2n  2n  1)  gu  gl  / 2  2n1  1
n 1
 256 . From Eq. (4),
2. d  1 and ( g u  g l ) / 2  2
g x  gu  gl  / 2  d   gu  gl  / 2  (2n  b)
 gu  gl  / 2  (2n  2n  1)  gu  gl  / 2  2n1  1
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

EX 1: The gray value of the given pixel PX is
assumed to be 12. The two neighboring
pixels have values 140 and 144.
d  (140  144) / 2  12  130
n  log 2 d  7
b  10111012  93
d   27  93  221
g x  (140  144) / 2  221  79
The PX is not used for embedding.
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

EX 2: The gray value of the given pixel PX is
assumed to be 166. The two neighboring
pixels have values 30 and 42.
d  (30  42) / 2  166  130
n  log 2 d  7
b  10111012  93
d   (27  93)  221
g x  (30  42) / 2  221  256
The PX is not used for embedding.
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12



Type 1
d  ( gu  gl  g r ) / 3  g x
g x  gu  gl  g r /3  d 
Type 2
d  ( gu  gl  gb ) / 3  g x
g x  gu  gl  gb /3  d 
Type 3
d  ( glu  g rb  glb  g rb ) / 4  g x
g x  glu  g ru  glb  g rb /4  d 
(8)
(9)
(10)
(11)
(12)
(13)
13
d  ( gu  gl  g r  gb ) / 4  g x
g x  gu  gl  g r  gb /4  d 
(14)
(15)
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15
16
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

There is no need of referencing the original
image when extracting the embedded data
from a stego-image.
Our experimental results have shown that the
proposed method provides a better way for
embedding large amount of data into cover
images without making noticeable distortions.
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