1. A Novel Reversible Data Embedding Scheme Using Dissimilar Pairing for Palette-based Images
Chair Professor Chin-Chen Chang
Feng Chia University
Tsing Hua University
Chung Cheng University

2. Outline Introduction The proposed scheme Experimental results
Conclusions

3. Introduction Information hiding Sender Secret data: 011 Receiver
Reconstructed image
Compression code: …
Color palette image
Compression code …
Secret data: 011

4. Palette image
Color-Palette image
Color palette

5. The proposed scheme (1/14)
Luminance-sorted palette
Red pixel value
Blue pixel value
Luminance value
Green pixel value

6. The proposed scheme (2/14)
Luminance-sorted palette
Sorted palette
Palette
Luminance value
Sort

7. The proposed scheme (3/14)
Dissimilar pairing
Sorted palette
2/n
n=16
Dissimilar

8. The proposed scheme (4/14)
PU = (RU, GU, BU) = (6, 9, 7)
PL= (RL, GL, BL) = (12, 10, 13)
= (9, 9, 10)
PUL = (RUL, GUL, BUL)
= (9, 8, 10)
The Reference Vector:
X：original pixel value
predicted pixel value

9. The proposed scheme (5/14)
Predicted indices Cp and Cq
Sorted palette
PLU Cp Cq

10. The proposed scheme (6/14)
Embedding policies
Case-A
Case-B
Extracting policies
Case-A'
Case-B'

11. The proposed scheme (7/14)
Embedding procedure (Case-A)
Cb: index of best cw
Db: dissimilar index of Cb
Cp and Cq: indices of predicted cw
Case-1: If Cb ≠ Cp and Cb ≠ Cq
Sorted palette
and d(Cb,Cp ) < d(Db, Cp)
and d(Cb, Cq) < d(Db, Cq)
(6, 9, 7) PU
PLU
(9, 8, 10) PL
(12, 10, 13)
Color image
Dp= 3
Dq= 4
Dissimilar
= (9, 9, 10) Cp
=11
Pc=(7, 9, 7)
d(Cb, Cp) = 29, d(Db, Cp) = 206, d(Cb, Cq) = 73, d(Db, Cq) =218 Cq
=12
Cb= 10
Dissimilar
Db= 2

12. The proposed scheme (8/14)
Embedding procedure (Case-A)
Original color index
Predicted color index
Cb= 10
Cp= 11
Cq= 12
Dissimilar
Dissimilar
Dissimilar
Db= 2
Dp= 3
Dq= 4
Embedding policy
If S=0 Encode with Cb
If S=1 Encode with Db
Ex: S=0
Encode with index Cb= 10
Size of codebook: 16, Cb = 10 = (1010)2
Compression codes: 1010

13. The proposed scheme (9/14)
Embedding procedure (Case-B)
Cb: best cw
Db: dissimilar cw of Cb
Cp and Cq: predicted cw
Case-2: If Cb = Cp or Cb = Cq
Sorted palette
or d(Cb,Cp ) ≧ d(Db, Cp)
or d(Cb, Cq) ≧ d(Db, Cq) PU
(6, 9, 7)
PLU
(9, 8, 10) PL
(12, 10, 13)
Color image
Dp= 3
Dq= 4
Dissimilar
= (9, 9, 10) Cp
=11
Pc=(8, 11, 12) Cq
=12
Cb= 11
Dissimilar
Db= 3

14. The proposed scheme (10/14)
Embedding procedure (Case-B)
Original color index
Predicted color index
Cb= 11
Cp= 11
Cq= 12
Dissimilar
Dissimilar
Dissimilar
Db= 3
Dp= 3
Dq= 4
Embedding policy
If S=00 Encode with Cp || Cb
If S=01 Encode with Cq || Cb
If S=10 Encode with Dp || Cb
If S=11 Encode with Dq || Cb
Ex: S=01
Encode with indices Cq||Cb=
Size of codebook: 16, Cq = 12 = (1100)2
Cb=11= (1011)2
Compression codes:

15. The proposed scheme (11/14)
Extracting and restoring policies (Case-A')
Compression codes: 1010
Sorted palette
(1010)2 = 10
Eb = 10
Dp and Dq: dissimilar cw of Cp and Cq
Cp and Cq: predicted cw
10≠11 10≠12
10≠3
10≠4
Case-A' : If Eb ≠ Cp and Eb ≠ Cq
and Eb ≠ Dp and Eb ≠ Dq PU
(6, 9, 7)
Dp= 3
Dq= 4
Dissimilar
PLU Cp
=11
(9, 8, 10) Cq
=12 PL
(12, 10, 13)
Color image
= (9, 9, 10)

16. The proposed scheme (12/14)
Extracting and restoring policies (Case-A')
Extracting and restoring policy
If d(Eb, Cp) < d(Db, Cp) and d(Eb, Cq) < d(Db, Cq)
Get S = 0 and restore the pixel with Eb
else Get S=1 and restore the pixel with Db
Ex:
Get compression index
Predicted color index
Eb= 10
Cp= 11
Cq= 12
Dissimilar
Dissimilar
Dissimilar
Db= 2
Dp= 3
Dq= 4
d(Cb, Cp) = 29, d(Db, Cp) = 206, d(Cb, Cq) = 73, d(Db, Cq) =218
It satisfies d(Eb, Cp) < d(Db, Cp) and d(Eb, Cq) < d(Db, Cq)
Get S = 0 and restore the pixel with Eb

17. The proposed scheme (13/14)
Extracting and restoring policies (Case-B')
Compression codes:
Sorted palette
(1100)2 = 12
Eb = 12
Dp and Dq: dissimilar cw of Cp and Cq
Cp and Cq: predicted cw
Case-B' : If Eb = Cp or Eb = Cq
or Eb = Dp or Eb = Dq
Get next compression codes Nb = (1011)2=11 PU
(6, 9, 7)
Dp= 3
Dq= 4
Dissimilar
PLU Cp
=11
(9, 8, 10) Cq
=12 PL
(12, 10, 13)
Color image
= (9, 9, 10)

18. The proposed scheme (14/14)
Extracting and restoring policies (Case-B')
Extracting and restoring policy
If Eb = Cp S = 00 and restore the pixel with Nb
If Eb = Cq S = 01 and restore the pixel with Nb
If Eb = Dp S = 10 and restore the pixel with Nb
If Eb = Dq S = 11 and restore the pixel with Nb
Ex:
Get compression indices
Predicted color index
Eb= 12
Cp= 11
Cq= 12
Nb= 11
Dissimilar
Dissimilar
Dp= 3
Dq= 4
It satisfies Eb = Cq
(12 = 12)
Get S = 01 and restore the pixel with Eb

19. Experimental results (1/2)
The color palette images with size 512 × 512
Original color palette image
PSNR: dB
PSNR: dB
PSNR: dB
Restored color palette image
PSNR: dB
PSNR: dB
PSNR: dB

20. Experimental results (2/2)
[1] Chan, C. S. and Chang, C. C., “A color image hiding scheme based on SMVQ and modulo operator,” Proceedings of the 13th International MultiMedia Modelling Conference (MMM2007), (Cham, T. J., Cai, J., Dorai, C., Rajan, D., Chua, T. S. and Chia, L. T. Eds.), Springer-Verlag, Part II, Singapore, 2007, pp. 461–470.
[3] Chang, C. C., Lin, C. C. and Chen, Y. H., “Hiding data in color palette images with hybrid strategies,” to appear in Imaging Science Journal, 2009.
[8] Fridrich, J., “A new steganographic method for palette-based images,” Proceedings of IS&T PICS Conference, Savannah, Georgia, 1999, pp. 285–289.
[10] Tzeng, C. H., Yang, Z. F. and Tsai, W. H., “Adaptive data hiding in palette images by color ordering and mapping with security protection,” IEEE Transactions on Communications, Vol. 52, No. 5, 2004, pp. 791–800.

21. Conclusions
A hybrid method consisting of pixel prediction and dissimilar concepts is conducted in this paper.
The proposed scheme has reversibility to restore the stego palette-based image to the original palette-based image.

22. Thank you so much!