1. Robustness Evaluation of Perceptual Watermarks
Author: Corina Nafornita
Source: International Symposium on
Signals,Circuits and Systems 2007
ISSCS 2007
Presented by:張景程
Data:

2. Outline
Introduction
Detection method
Simulation result
Conclusion

3. Introduction In a watermarking system, robustness
evaluation should be made if invisibility criteria are satisfied.
Several watermarked images were tested for different types of attacks (JPEG compression, median filtering, resizing, cropping and gamma correction) in order to see the effect of these attacks on the detector results

4. Detection method(1/6)
DWT
4-level
DWT
1-levels
watermark

5. Detection method(2/6)
All coefficients from the subbands from level 0 by addition:
: embedded watermark in level 0
: embedding strength
:a weighing function, which is a half of the
step

6. Detection method(3/6) The step with three factors:
First factor is the sensitivity to noise depending on
the orientation and on the level of detail:

7. Detection method(4/6)
Second factor takes into account the local brightness based on the gray level values of the low pass version of the image:
too dark
original thumbnail
Brightness proportion
switch Coordinate
embed

8. Detection method(5/6)
Third factor is computed in the neighborhood of the pixel.
It including two parts :
First is the local mean square value of the DWT coefficients
in all detail subbands
Second is the local variance of the low-pass subband.

9. Level=0 K=3 K=2 K=1 K=0 average quare coefficients
Original image proportion to average
K=3
K=2
K=1
K=0
average quare coefficients

10. Variance If square coefficients is and average is Z Coordinate

11. Detection method(6/6)
Finally, detection is made using the correlation between the marked DWT coefficients and the watermarking sequence to be tested for presence:
Average of the three part

12. Simulation results AT level =0 with different embedding strengths .
For =0.2(Method 1) and =0.4 (Method 2)

13. Different types of attack(1/2)

14. Different types of attack(2/2)

15. Conclusions The two methods were comparable and they
successfully detected the watermark only in the
case of mild attacks