The encryption of the watermark and the choice of embedded areas based on the perceptivity not only confer the watermark with good invisibility but also with good robustness.
Since the approximation coefficients are supposed to be relatively stable and less sensitive to slight changes of the audio signal, they are ideal embedding area.
More formally, for each embedding area g i (x, y), i = 1... M (where M is the number of feature points) of the normalized image we additively embed the DCT-domain watermark as follows D C T ( g i w ( x, y ) ) = D C T ( g i ( x, y ) ) + α ⋅ W ( u, v ) (26).
Watermarking methods Block size of original image Mohanty's method [24] Asatryan's method [27] Proposed method Selection embedding area procedure (1) Find a most perceptually significant set of blocks constituting a subimage (equal to size of watermark) with respect to human perception such as Texture, Location, Contrast, Luminance, and Edginess in original image.
where i = 1,..., M, w i (x, y) is the image with same size as f x, y) and non-zero only in the i th embedding area (where w o is located), and f 0 w ( x, y ) = f ( x, y ).
In this section, the differences and excellences of proposed method with two related methods [24, 27] are introduced in four conventional different steps of watermarking methods: (1) selecting embedding area procedure, (2) watermark creation procedure, (3) inserting procedure, (4) extracting procedure.
We can notice that some embedding areas may overlap because of the proximity of the corresponding feature points.
The next step is to extract a set of feature points that will act as centers of the watermark embedding areas.
The CNTs had the different embedded surface area and functional groups.
Hence, by successive reflection across geodesic arcs on the boundary, one obtains a family of embedded least area disks (S_{i,j} subset overline{U}_{i,j}) with boundary (partial S_{i,j} = Delta _{i,j}).
