The real and imaginary components of a complex Gabor filter are phase sensitive, i.e., as a consequence their response to a sinusoid is another sinusoid (see Figure 1.2). By getting the magnitude of the output (square root of the sum of squared

Coefficients a and b control the low and high frequency ranges that the watermark affects. Because of the watermark invariant properties, we embed the watermark only in the Fourier descr iptor magnitude. We use the inverse Fourier transform of the Fo