1. Data Hiding Watermarking for Halftone Images
IEEE Transactions on Image Processing,
VOL.11,No.4,April 2002
Ming Sun Fu ,Student Member ,IEEE
Oscar C.Au ,Senior Member ,IEEE
Reporter:Liu Rui
May 20th,2008

2. Outline Introduction Data Hiding Without Original Multitone Image
Data Hiding with Original Multitone Image
Experimental Results
Conclusion

3. Introduction Data Hiding for halftone images
Data Hiding Smart Pair Toggling(DHSPT)
Modified Data Hiding Error Diffusion (MDHED)

4. Data Hiding Without Original Multitone Image
Data Hiding Self Toggling(DHST)
Data Hiding Pair Toggling(DHPT)
Data Hiding Smart Pair Toggling(DHSPT)

5. Data Hiding Self Toggling(DHST)
A pseudo-random number generator with a seed is used to identify the pseudo-random location where the data is embedded.
The pixel at the location is 0 or 1 according to the data bit to be embedded.

6. Data Hiding Self Toggling(DHST)1 1
1,3
1,8
2,5
2,9 ……
8,1 1 … ……
pseudo-random
number generator
host image
Embedded data

7. Data Hiding Pair Toggling(DHPT)
Master pixel：
A pixel at a pseudo-random location needs to self-toggle
Slave pixel：
There are M pixels of opposite color in the
neighborhood.
One of the M pixels is chosen to self-toggle also.
If M equals zero,no compelmentary toggling is performed 1 1

8. Data Hiding by Smart PairToggling
DHSPT is the same as DHPT except that the choice of the slave pixel for complementary toggling is not random.
The candidate with minimum after-toggle “connection” conafter(m,n)

9. Data Hiding by Smart PairTogglingX1
X 2 X3 X4 X0 X5 X6 X7 X8
Where w(i) = 1 for i = 1, 3, 6, 8 and w(i) = 2 for i = 2, 4, 5, 7

10. Data Hiding by Smart PairToggling
con(m,n)min=0
con(m,n)max=12
If x0 is toggled to x0 and the eight neighboring neighbors are not changed,then f(x0,xi)+f(x0,xi)=1 and 1 1

11. conafter(2,2)=1×0+2×1+1×1+2×1+2×1+1×0+2×1+1×0=91
conbefore(2,2)=1+1+1=3
conafter(2,2)=1×0+2×1+1×1+2×1+2×1+1×0+2×1+1×0=9

12. f(x0,xi)+f(x0,xi)=0 1 1
If the master and slave are horizontal or vertical neighbors
W(i)=2,conbefore(m,n)+conafter(m,n)=10
Otherwise , w(i)=1,conbefore(m,n)+conafter(m,n)=11

13. conafter(1,2)=10-(2. 1+1. 1+1. 1)=6 conafter(1,3)=11-(2. 1+2
conafter(1,2)=10-(2*1+1*1+1*1)=6 conafter(1,3)=11-(2*1+2*1)=7 conafter(2,1)=10-(1*1+1*1)=8 conafter(2,3)=10-(1*1+2*1+1*1)=5 conafter(3,2)=10-(1*1+1*1)=8 1 1 1

14. Data Hiding With Original Multitone Image
Data Hiding Error Diffusion(DHED)
Modified Data Hiding Error Diffusion(MDHED)
Both DHED and MDHED start off with DHST.
DHED and MDHED use error diffusion to diffuse the self-toggling distortion to many neighboring pixels to achieve higher visual quality.

15. Error Diffusion The algorithm is a "neighborhood" algorithm.x 7 3 5 1
Floyd and Steinberg (1975)

16. Error Diffusion Dithering by Floyd-Steinberg error diffusion
threshold = (black + white)/2
For all x and y do
if f(x,y)<threshold then
g(x,y)=black
e=f(x,y) - black
else
g(x,y)=white
e=f(x,y) – white
end if
f(x+1,y)= f(x+1,y)+7e/16
f(x-1,y+1)= f(x-1,y+1)+3e/16
f(x,y+1)= f(x,y+1)+5e/16
f(x+1,y+1)= f(x+1,y+1)+e/16
End for

17. Error Diffusion e=140-255 = -115 Threshold = 128 255 140 95 178 53 98
140 95
178 53 98
255 95
178 53 98
e= = -115

18. Error Diffusion x 7 3 5 1
255 45
156 17 91

19. Data Hiding Error Diffusion(DHED)
Step 1 25 30 90
200
150 40 75 80
110
100
160 65 85
180 60 70
190
230
120 50
170
2,3
3,6
4,2 ……
6,3
255 ……
255
pseudo-random
number generator
Host Image

20. Data Hiding Error Diffusion(DHED)
Step 2
205 70
190 80
140 95
170 50
100 x 7 3 5 1
255
140 45
148 14 92
e= = -115

21. Data Hiding Error Diffusion(DHED)x 7 3 5 1
205 70
190 80
140 95
170 50
100
e(1,1)= e(1,2)=70
e(1,3)= e(2,1)=80
a(2,2)=[(-50)+5*(70)+3*(-65)+7*(80)]/16=42
f(2,2)=140+42=182
y(2,2)=255
e(2,2)=-73
255
140 95
170 50
100 1 5 3 7 x

22. Modified Data Hiding Error Diffusion(MDHED)
In MDHED, the DHST is applied as in DHED.
The error diffusion is modified to become noncausal such that the error is fed not only to future pixels but also to past pixels
C11
C12
C13
C21

23. Modified Data Hiding Error Diffusion(MDHED)

24. Modified Data Hiding Error Diffusion(MDHED)25 30 90
200
150 40 75
110
100
160 65 85
180
255
190
230
120 50 80
170 70 60
255
200
190
230
120 50 80
160
170 70 30 60
255
255
eguess(4,2)=70-0=70
a(3,3)=【75+5×（80-0）+3×(110-0)+7×（85-0）】/16=88
f(3,3)=x(3,3)+a(3,3)+1/8×1/3×70= =191
y(3,3)=255
e(3,3)=--64
eguess(4,2)=70-0=70
a(4,1)=【5×（65-0）+3×(85-0】/16=35
f(4,1)=x(4,1)+a(4,1)+3/8×1/3×70=74
y(4,1)=0
e(4,1)=74
eguess(4,2)=70-0=70
a(3,2)=【40+5×（75-0）+7×（65-0）】/16=51
f(3,2)=x(3,2)+a(3,2)+3/8×1/3×70= =145
y(3,2)=255
e(3,2)=-110
eguess(4,2)=70-0=70
a(3,1)=【0+5×（85-0）+3×（100-0）+7×（30-0）】/16=58
f(3,1)=x(3,1)+a(3,1)+1/8×1/3×70= =126
y(3,1)=0
e(3,1)=126

25. Modified Data Hiding Error Diffusion(MDHED)
255
200
190
230
120 50 80
160
170 70 30 60
a(4,2)=63
e(4,2)=110
f(4,2)=133

26. Experimental Results

27. Experimental Results

28. Experimental Results

29. Experimental Results

30. Conclusion
When the original multitone image is not avaible,DHSPT can hide a large amount of data in halftone images.
When the original multitone image is avaible and the halftoning method is error diffusion,MDHED can hide data in the halftone images .the experimental results suggest that the resulting image quality is very high.