High-capacity image hiding scheme based on vector quantization

1. High-capacity image hiding scheme based on vector quantization Authors: Yu-Chen Hu Source: Pattern Recognition, vol. 39, pp. 1715-1724, 2006 Speaker: Shu-Fen Chiou(邱淑芬) Date: 2006/10/19

2. Outline • Introduction • Proposed method • Experimental results • Conclusion • Comment

3. Introduction • This method is hiding multiple secret images into a host image of the same size. • The proposed scheme provides a higher hiding capacity.

4. Hiding bits sno: total number of secret images Nc: the size of VQ codebook k: the vector dimension rmax: The maximal number of modified bits

5. Training codebook Random seed rs Codebook is sorted by mean values of codewords

6. VQ Codebook 0 1 2 (20,45,…,76) 253 254 Original image Index table 255

7. AAD • Design HCT

8. Hiding s(i,j)=00 127+1 Host pixel h(i,j) HCT(i,j)=2 b(i,j)=127 mod 22=3 d(i,j)=0-3=-3 h’(i,j) d’(i,j)=-3+22=1 -22+1<=d(i,j) <-(22-1)/2=-1.5

9. Index compression Encode: ‘0’+’01’ RANG=4

10. Index compression Encode: ‘10’+’1’+’00110’

11. Index compression Encode: ‘11’+’10000000’

12. Encrypt • Compressed index table is encrypted by DES cryptosystem suing the secret key sk • W, h, sno, Nc, k, rs, pk, RANG, and ThDIST are encrypted by DES cryptosystem also using the same secret key sk

13. The secret extraction procedure • Extract w, h, sno, Nc, two random seeds key rsand pk, RANG, THDIFFanddeterminermax. • Generate the VQ codebook with Nc codeword using H' with random seed rs. • Obtain a serial of random number by pk. • To rebuild the original index table by RANGandTHDIFF.

14. Experimental results

15. Experimental results

16. Experimental results Comparative storage cost (unit: bits) of the proposed scheme (PS) and the proposed scheme without index compression (PS').

17. Experimental results Provide an average of 1.304dB image quality gain.

18. Experimental results Image qualities of the stego-images of the proposed scheme

19. Experimental results

20. Experimental results 1024 codebook

21. Conclusion • A novel image hiding scheme based on vector quantization is proposed. • The proposed scheme is secure.

22. Comments • 用VQ將secret images壓縮，所以secret images取出後會失真。 • 將index table再壓縮，隱藏數量變少。