1. Halftone Image Data Hiding with Block-Overlapping Parity Check
Richard Y. M. Li, Oscar C. Au, Carman K. M. Yuk,
Shu-Kei Yip , Sui-Yuk Lam
Department of Electronic and Computer Engineering
The Hong Kong University of Science and Technology
Reporter: Liu Rui

2. Outline Introduction The Proposed BOPC Algorithm Experimental Results
Conclusion

3. Introduction Hiding information into the digital media
A new data hiding algorithm for halftone images named Block-Overlapping Parity Check(BOPC)
Based on Data Hiding Smart Pair Toggling(DHSPT)
Reduce the number of pair toggling required in DHSPT

4. Data Hiding Smart Pair Toggling(DHSPT)
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.

5. Master pixel： Slave pixel：
A pixel at a pseudo-random location needs to self-toggle
There are M pixels of opposite color in the
neighborhood.
Slave pixel：
One of the M pixels is chosen to self-toggle also. 1 1

6. Data Hiding Smart Pair Toggling(DHSPT)X1
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

7. Block-Overlapping Parity Check(BOPC)
Master map
Parity map
Toggle map

8. Master map M S
1,1
121,133
1,2
193,34 ……
2,1
34,351
2,2
543,68 1 … 1
……………………1………………
…………0………………………………………………………………………………1………………………1……………………0……………………………………………………………………1……………………
Master Map
Host Image
Location Mapping Table
A pseudo-random number generator is used to generate a set of (2Lx+1)*(2Ly+1) pseudo-random

9. Parity map

10. Parity map Master Map Parity Map 1 1 1 1 P11=(M11+M12+M13+M21+M22+1 1 1
P11=(M11+M12+M13+M21+M22+
M23+M31+M32+M33)mod 2
=( )mod 2 =1
P12=(M13+M14+M15+M23+M24+
M25+M33+M34+M35)mod 2
=( )mod 2 =1

11. Toggle map Tij=Pij⊕Lij
If Pij and Lij happen to be the same,Tij will be zero and no toggling is need.

12. Toggle map 1 L 1 ⊕ 1 P
Toggle Map

13. Bubble Formation 1 1 3 2 4 1 3 3 2 2
Bubble Formation 2 4 4 2 4 4

14. Watermark Insertion

15. Example M 1 1 M’ 3 1 T’ 1 P 1 ⊕ 1 P’ 1 L T

16. Experimental Results

18. Conclusion Can hide a large amount of data in halftone images.
Comparing with DHSPT,BOPC can reduce half of the pair toggling required.
Has a high MPSNR and good visual quality as shown in the experimental results.