1. A steganographic method for digital images using side match
Source: Pattern Recognition Letters, Volume: 25,
Issue: 12, Sep., 2004, pp
Author: Chin-Chen Chang and Hsien-Wen Tseng
Speaker: Na-I Wu (吳男益)

2. Outline Introductions The Proposed Scheme The Experimental Results
Conclusions

3. Introduction Edge areas: Hide more secret data
Smooth areas: Hide less secret data
Side Match
Two-sided
three-sided

4. The Proposed Scheme Two-sided match steganography
Pu: The pixel value say, gu
Px: The pixel value say, gx
PL: The pixel value say, gl
d = (gu +gl) / 2 – gx
If (d is -1, 0, 1)
one bit hide into Px by LSB
end
Ex:
gu=100, gx=101, gu=100,d=( )/2-101=-1
So, gx= , if secret data is “1” No Modify
if secret data is “0”  (2)=100(10)

5. Two-sided match steganography
Embedding Algorithm
d = (gu +gl) / 2 – gx
14 = (40 +82) / 2 – 47
計算要藏幾個bit
3 = log2 |14|
要藏3 bits101。
n = log2 |d|
n: 要藏的bit數。
(1)將n轉換成十進制b
(2)計算新的差值
d’=2n+b, if d > 1
d’=-(2n+b), if d<1
13=23+5, if d > 1
重新調整gx值
gx=(gu +gl)/2 – d’
48 = (40 +82) / 2 – 13

6. Two-sided match steganography
Extracting Algorithm
d= (40+82)/2-48=13 40 48 82
3 = log2 |13|
表示有藏3 bits
13 – 23 = 5
5 = 101(2)

7. Three-sided match steganography
d = (gu +gl+gr) / 3 – gx
g’x = (gu +gl+gr) / 3 – d’

8. Four-sided match steganography
d = (gu +gl+gr+gb) / 4 – gx
g’x = (gu +gl+gr+gb) / 4 – d’

9. The Experimental Results
Methods
Lenna
Baboon
Capacity
PSNR
2-sided
389,004
41.22
660,725
33.53
3-sided
267,242
45.03
483,758
34.93
4-sided
164,538
48.18
298,413
38.56

10. Conclusions
An efficient steganographic method to embed secret information into images without producing perceptible distortions.
There is no need of referencing the original image when extracting the secret data
The pixels in edge areas may hide more secret data than smooth ares.