A watermark is a signal added to digital data (audio, video and still images) that can
be detected or extracted later to make an assertion about the data. Embedding a
watermark in an image means inserting information in the image, such that the image
quality does not deteriorate significantly. In recent years, Internet system has become
popular for transmitting and receiving digital data. Hence it is essential to secure the
digital protection better. The digital watermarking is an effective method to solve
the problem (Arnold et al., 2003). Many watermarking schemes have been introduced
for digital images, spatial and transform domain techniques are the most common
(Bender et al., 1996; Banf et al., 2002; Ganic and Eskicioglu, 2004; and Guangmin,
2007). Spatial techniques adjust the lower-order bits of the image pixel to guarantee
imperceptibility. Spectral or transform techniques incorporate the watermark into the
transform coefficients of an image. Transform-based algorithms allow one to easily
place the watermark in the perceptually significant parts of an image. This leads to
a mark that is more robust to attacks, since it is harder to remove without distorting
the image (Hartung and Kutter, 1999; Kong et al., 2003; and Guangmin, 2007). Popular
transform include Discrete Cosine Transform (DCT) and the wavelet transform. There
are various schemes for embedding digital watermarks into grayscale images at present (Guangmin, 2007; and Vikas, 2007), however, just embedding watermarks into
color image is not sufficient. As in practical applications, color images have acquired
a significant position, hence it is important to research them further.
Out of the three channels (red, green and blue), red channel is the most robust
against JPEG compression attack, while blue channel is the least. Therefore, hidden
watermark information is more secured in the red channel than in blue channel.
Guangmin (2007) proposed a scheme for digital watermarking of color images based
on Discrete Wavelet Transform (DWT), which transforms original color image into YIQ
model and embeds the watermark in the Y and Q component (Hartung and Kutter,
1999). Mei et al. (2001) proposed a scheme for hiding watermark in the low frequency
coefficients of 8 8 DCT blocks of the red, green and blue channels (Kong et al.,
2003). Banf et al., (2002) proposed a scheme, in which red, green and blue channels
were transformed by full frame DCT, and selected the low frequency coefficients to
hide watermark (Kundur and Hatzinakos, 1999).
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