A Novel Comprehensive Watermarking Scheme for Color Images

Algorithm 6

Rotation correction.

(1) Step 1: extract the feature points of the attacked image through the SIFT method, and generate collection S.
(2) Step 2: compare corresponding points in collection S and the collection of recorded feature points as T, and if the comparison is successful, record the coordinates of the feature points on the original graph and attacked image to produce the feature point pair.
(3) Step 3: take any two matching successful feature point pairs, and the two points from S and the two points from T are recorded to generate vectors and , respectively. The angle between the vector and the vector is calculated as ,
	where |a| and |b| represent the module of a and b, respectively. Traverse all the point pairs to generate collection A which consists of all angles φ [15].
(4) Step 4: use the box plot to clean collection A. Calculate the next quartile , upper quartile , and intermediate quartile extreme difference . Remove the outlier values which are greater than or less than , and generate collection B.
(5) Step 5: calculate the mean of all angles in collection B:
	where represents the number of elements in collection B. Refer to it as the rotation recovery angle.