A New Digital Watermarking Scheme Applying Locally the Wavelet Transform Author: Minoru Kuribayashi, Hatsukazu Tanaka Source: IEICE Trans. on Fundamentals of Electronics, Communications and Computer Sciences, Vol. E84-A, No. 10, Oct. 2001, pp. 2500-2507 Speaker: Henry Chou Date: 2002/12/26 Department of Computer Science, University of Regina At Regina, Canada

Outline Introduction Proposed Scheme I Proposed Scheme II Experimental Results Conclusions

Introduction Haar Wavelet Transform Attacks on Watermarking Signal processing such as filtering, lossy compression, additive noise. Geometric transformations such as rotation, scaling, clipping, shifting.

Haar Wavelet Transform(cont.) Phase 1) Horizontal: A B C D E F G H I J K L M N O P A+B C+D A-B C-D E+F G+H E-F G-H I+J K+L I-J K-L M+N O+P M-N O-P ㄅ ㄆ ㄇ ㄈ ㄉ ㄊ ㄋ ㄌ ㄍ ㄎ ㄏ ㄐ ㄑ ㄒ ㄓ ㄔ Phase 2) Vertical: ㄅ ㄆ ㄇ ㄈ ㄉ ㄊ ㄋ ㄌ ㄍ ㄎ ㄏ ㄐ ㄑ ㄒ ㄓ ㄔ ㄅ+ㄉ ㄆ+ㄊ ㄇ+ㄋ ㄈ+ㄌ ㄍ+ㄑ ㄎ+ㄒ ㄏ+ㄓ ㄐ+ㄔ ㄅ-ㄉ ㄆ-ㄊ ㄇ-ㄋ ㄈ-ㄌ ㄍ-ㄑ ㄎ-ㄒ ㄏ-ㄓ ㄐ-ㄔ

Haar Wavelet Transform(cont.) Phase 1) Horizontal: Example 20 15 30 17 16 31 22 18 25 21 19 35 50 5 10 33 53 1 9 42 -3 -8 43 37 -1 35 50 5 10 33 53 1 9 42 -3 -8 43 37 -1 Phase 2) Vertical: 35 50 5 10 33 53 1 9 42 -3 -8 43 37 -1 68 103 6 19 76 79 -4 -7 2 -3 4 1 -10 5 -2 -9 326 -38 6 19 16 -32 2 -7 -3 4 1 -10 5 -2 -9 (Level one is done) (Level two is done)

Introduction (cont.) StirMark attack Introduces local/global geometric distortions perceptually close to the original image. Make the orthogonal axes out of sync. So the correct frequency coefficients can't be correctly extracted from the attacked image. Combines other attacks such as JPEG compression, additive noise, etc.

Introduction (cont.) StirMark Example

Introduction (cont.) StirMark Example (cont.) Original image:

Introduction (cont.) StirMark Example (cont.) Distorted image.

Proposed Scheme I Assumption: Trusted center. Author registers watermarked image with the trusted center. Watermark embedded into the frequency domain, thus spread over the whole image, for better tolerance to attacks. Wavelet transform applied to sub-images consisting of local blocks.

Proposed Scheme I (cont.) Embedding: 2 watermark bits embedded in each iteration.

Proposed Scheme I (cont.) Searching Protocol:

Proposed Scheme I (cont.) Extracting: Construct a sub-image from the four blocks of the distorted image. Calculate the difference between the DCT coefficients of the original and distorted image that hides the watermark bit Watermark bit =

Proposed Scheme II Hiding watermark data in high frequency elements is less perceptible. Only blocks with variances larger than a predefined criteria are selected to hide data.

Experimental Results Degradation Trade-off between quality and robustness: 8  m  12

Experimental Results (cont.) Degradation Fig. 9 Distortions at a flat region becomes obvious. Fig. 10 Selecting only high frequency blocks for embedding.

Experimental Results (cont.) Degradation (cont.) Trade-off between quality and robustness: 8  m  12

Experimental Results (cont.) Degradation (cont.)

Experimental Results (cont.) Searching Distance “correct” means NO error occurred in extraction. d = 12 is enough for StirMark attack.

Experimental Results (cont.) StirMark Attack (carried out 104 times) Even when m = 12, the tolerance is not enough. However, number of error bits is small. Can be mended with correction codes. Errors decrease as m increases.

Experimental Results (cont.) StirMark Attack (cont.) Statistics of other images resemble those of “lenna” shows the number of errors is independent of characteristics of images.

Experimental Results (cont.) StirMark Attack (cont.) The robustness and PSNR are independent of the embedding coefficient.

Experimental Results (cont.) JPEG Compression (based on 103 experiments) For m  12, can tolerate higher compression.

Experimental Results (cont.) JPEG Compression (cont.) Even for m = 8, number of errors is almost less than 3bits for quality over 30%.

Experimental Results (cont.) JPEG Compression (cont.) For m = 20, the tolerance for JPEG compression at low quality is still good.

Conclusion A robust watermarking scheme is proposed. Hard to remove Hard to forge – needs to know the selected blocks and PN sequence. Withstands distortions of geometric transforms - recovers synchronization by searching protocol.