Blind and Secured Adaptive Digital Image Watermarking Approach for High Imperceptibility and Robustness

. 2021 Dec 8;23(12):1650. doi: 10.3390/e23121650

Algorithm 2 Watermark extraction.

Require:
Watermarked image ( $C_{1}$ ), m, s, Random key ( $R_{k e y}$ ), $α$
Ensure:
Extracted Watermark $(E W)$
1:
Apply 1-IWT to $C_{1}$ , to obtain $L L^{1}$ , $L H^{1}$ , $H L^{1}$ and $H H^{1}$ sub-bands
2:
Apply SVD to $L H^{1}$ and $H L^{1}$ sub-bands to obtain $U_{L H}^{1}, S_{L H}^{1}, V_{L H}^{1}, U_{H L}^{1}, S_{H L}^{1}, V_{H L}^{1}$
3:
Divide $S_{L H}^{1}$ and $S_{H L}^{1}$ into $4 \times 4$ non-overlapping blocks.
4:
Select low entropy blocks $(B_{L H}^{1}, B_{H L}^{1})$ .
5:
Determine watermark extraction positions $(P_{1} a n d P_{2})$ using BBS Pseudo random series generated by using $m a n d s$ .
6:
Extract watermark vector from $S_{L H}^{1}$ and $S_{H L}^{1}$ using the steps below:

$V_{o d d}^{11}$ ← $(B_{L H}^{1} (P_{1}, P_{2}) - B_{L H} (P_{1}, P_{2})) / α$

$V_{e v e n}^{11}$ ← $(B_{H L}^{1} (P_{1}, P_{2}) - B_{H L} (P_{1}, P_{2})) / α$
7:
Generate a pseudo random key ( $P R_{k e y}$ ) using $R_{k e y}$ .
8:
Re-shuffle the extracted watermark vectors i.e., odd $(V_{o d d}^{11})$ and even $(V_{e v e n}^{11})$ vectors using $P R_{k e y}$ .

$E V_{o d d}$ ← $P R_{k e y}$ · $V_{o d d}^{11}$

$E V_{e v e n}$ ← $P R_{k e y}$ · $V_{e v e n}^{11}$
9:
Combine $E V_{o d d}$ and $E V_{e v e n}$ to get the extracted watermark.

$E W$ ← $E V_{o d d} + E V_{e v e n}$