1. Hiding Data in a Color Palette Image with Hybrid Strategies
(to appear in Imaging Science Journal, 2008)
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 Compression code 1000011010…
Secret data: 011
Receiver
Reconstructed Image
Sender
Compression Code: …
Host Image
Secret data: 011

4. Palette Image
Color-Palette Image
Color Palette

5. The proposed scheme (1/11)
Luminance-sorted Palette
Red pixel value
Blue pixel value
Luminance value
Green pixel value

6. The proposed scheme (2/11)
Luminance-sorted Palette

7. The proposed scheme (3/11)
PU = (RU, GU, BU) = (6, 9, 7)
PL= (RL, GL, BL) = (12, 10, 13)
= (9, 9, 10)
The Reference Vector:
X：original pixel value
predicted pixel value

8. The proposed scheme (4/11)

9. The size of index table is 4×16
Tradition Method
Ex: X1 X2 X3 X4 X5 X6 X7 X8 X9
X10
X11
X12
X13
X14
X15
X16 11 8 10 13 2 12 7 5 9 3
Encoding
Original Pixels
Index Table
The size of index table is 4×16
4 bits to encode a pixel.
Color Palette

10. Prediction Method (1/2) 11 8 10 13 X6 X7 X8 12 X10 X11 X12 X14 X15 X16
= (9, 9, 10)
Color palette
Best codeword
Original Pixels

11. Prediction Method (2/2)
If (Distortion < 10) encode it with state palette
Else encode it with tradition method
Threshold T
X6 = (8, 10, 11)
K2 = (8, 11, 12) K
Distortion = = 2 11 8 10 13 2 3 12 1
0, 11
0, 8
0, 10
0, 13
1, 2
1, 3
0, 2
0, 12
1, 0
1, 1
Insert indicator
Use 5 bits to encode this pixel
Use 3 bits to encode this pixel
Index Table
Index Table
The size of index table is 3×8 + 5 × 8

12. The proposed scheme (5/11)

13. The Proposed Scheme (6/11)
If Distortion (K0, Original Pixel X) < threshold T
Output: 1  indicator
100  compression code
This is, output (1, 4) ≡ (1, 100) 4
Phase-1 data embedding
Assume that the
secret data is
001 K
Else if Distortion (K0, Original Pixel X)
> threshold T
Use sorted color palette to embed secret data (Phase-2 data embedding)

14. The Proposed Scheme (7/11)
Phase-2 data embedding
X = (8, 10, 11) P
Output (0, 7) ≡ (0, 0111)
If D(X', P12) < D(X', P7)
Secret data: 0
Indicator: 0
Secret data: 1
Output (0, 12) ≡ (0, 1100)
Else if D(X', P12) > D(X', P7)
Secret data: 0
Indicator: 0
Secret data: 1
Output (0, 0, 12) ≡ (0, 0000, 1100)
Output (0, 15, 12) ≡ (0, 1111, 1100)
X’s best codeword

15. The Proposed Scheme (8/11)
Extracting Procedure

16. The Proposed Scheme (9/11)
Ex: (indicator, compression code) = (1, 100)
∵4>3 ∴ Decode with K0
Phase-1 extracting policy
The retrieved secret data is 001 K

17. The Proposed Scheme (10/11)
Ex: (indicator, compression code) = (0, 0000, 1100)
Phase-2 extracting policy P
Secret data is 0
Decoded pixel with P12

18. The Proposed Scheme (11/11)
Ex: (indicator, compression code) = (0, 0111)
Phase-2 extracting policy P
If D(X', P12) < D(X', P7)
Decode the pixel with P12 and retrieve secret data 1
Else
Decode the pixel with P7
and retrieve secret data 0

19. Experimental results (1/3)
The color host images with size 512 × 512
Lena
Pepper
Baboon
Three stego-images for threshold T=20
PSNR: dB
Hiding capacity: 304 Kb
PSNR: dB
PSNR: dB
Hiding capacity: 271Kb
Hiding capacity: 257 Kb

20. Experimental results (2/3)

21. Experimental results (3/3)

22. Conclusions
A novel scheme is proposed to hide large amount of secret data into a color image.
The qualities of the reconstructed images are good.

23. Thank you so much!