# A Large Capacity Histogram-Based Watermarking Algorithm for Three Consecutive Bins
## 4 Experimental Results and Analysis
### Watermark Robustness  
Some common attacks, such as cropping, crossed attack, rotation distortions, AWGN (additive white Gaussian noise) attack, and JPEG compression attack, were used to examine the robustness of the watermark with our method. We compared this with those suggested in [13; 14; 15]. The main image editing and attacking tool used in our experiments was MATLAB. For the four test images, we set the experimental parameters as the following: (1) the bin's width was set as two; (2) the threshold was set as five; (3) the capacity was set as 24 bits. Without loss of generality, we take Barbara as an example of the attacked image. Corresponding to the simulation results, we have the following observations:  
1. Cropping: The cropping ranges from 5-50% with the interval of 5%. Figure 5 shows the watermarked image with the cropping of 5%, 25%, and 50%, respectively. Figure 6a,b presents the accuracy of watermark extraction when the watermarked image suffered from different levels of cropping attack. 2. Crossed attack: The number of lines increased from 1-8. This was set as 1, 4, and 8, respectively, as shown in Figure 7. The corresponding extraction results after crossed attack are given in Figure 6c,d. 3. Rotation distortions: The rotation angles ranged from 3\({}^{\circ}\)-30\({}^{\circ}\) with the interval of 3\({}^{\circ}\). From Figure 8, one can understand the watermarked image with rotation angles of 3\({}^{\circ}\), 18\({}^{\circ}\), and 30\({}^{\circ}\), respectively. Figure 6e,f presents the results after rotation attack. 4. AWGN attack: The standard deviation of AWGN was set from 1-10. Similarly, we can see from Figure 6g,h that the watermarked image could resist AWGN attack well. 5. JPEG compression: The quality factor of JPEG compression was changed from 80-100. Figure 6i,j provides a significant indication that the proposed watermark method was equipped with the capability of resisting JPEG compression. Here, it should be emphasized that the BER (bit error rate) of our method was a little higher than the other methods; this is because approximately equal adjacent bins were considered in our method, and thus, this may have increased the error rate of watermark extraction. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Payload (bit)** & **32** & **48** & **56** & **63** \\ \hline \multirow{6}{*}{Averaged PSNR (dB)} & [PERSON] et al. [13] & 46.85 & 43.97 & - & - \\  & [PERSON] et al. [17] & 46.12 & 43.46 & - & - \\ \cline{1-1}  & Scheme 1 [18] & 46.92 & 44.07 & 38.99 & 42.37 \\ \cline{1-1}  & Scheme 2 [18] & 46.92 & 43.69 & 43.40 & 41.67 \\ \cline{1-1}  & The proposed & **56.84** & **55.04** & **53.89** & **53.51** \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of PSNRs among different algorithms. Figure 5: Examples of local cropping with different percentages for Barbara. Figure 6: _Cont._  
From the above observations, the proposed method was powerful in robustness against geometric attacks and common image processing operations. Because the histogram of the modified image incurred during the cropping and crossed attacks kept approximately the same as that of the original image without suffering from attack, the watermark algorithm had higher robustness to cropping and crossed attacks. When suffering from AWGN and JPEG compression attacks, the embedded watermark information could still be effectively extracted, indicating that the functionality of resisting  
Figure 8: Examples of different rotation angles for Barbara. Figure 6: Robustness to cropping, crossed, and rotation attack for [PERSON] and [PERSON] (\(M=2\), \(T=5\), and \(C=24\)). (**a,b**) The cropped watermarked images of [PERSON] and [PERSON]; (**c,d**) the crossed watermarked images of [PERSON] and [PERSON]; (**e,f**) the rotation watermarked images of [PERSON] and [PERSON]; (**g,h**) the AWGN watermarked images of [PERSON] and [PERSON]; (**i,j**) the JPEG watermarked images of [PERSON] and [PERSON]. Figure 7: Examples of crossed attack with different numbers of lines for Barbara.