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 http://msn.iecs.fcu.edu.tw/~ccc

Outline Introduction The proposed scheme Experimental results Conclusions

Introduction Information Hiding Compression code 1000011010… Secret data: 011 Receiver Reconstructed Image Sender Compression Code: 1000011010… Host Image Secret data: 011

Palette Image Color-Palette Image Color Palette

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

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

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

The proposed scheme (4/11)

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

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

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 = 02+12+12 = 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

The proposed scheme (5/11)

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)

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

The Proposed Scheme (8/11) Extracting Procedure

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

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

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

Experimental results (1/3) The color host images with size 512 × 512 Lena Pepper Baboon Three stego-images for threshold T=20 PSNR: 35.422 dB Hiding capacity: 304 Kb PSNR: 33.005 dB PSNR: 30.827 dB Hiding capacity: 271Kb Hiding capacity: 257 Kb

Experimental results (2/3)

Experimental results (3/3)

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.

Thank you so much!