Color Watermarking Algorithm Based on Modified QFFT and DCT

A new color watermarking algorithm of colored images based on modified quaternion fast Fourier transform (QFFT) and discrete cosine transform (DCT) is presented. By modifying the image vector μ, the real part and imaginary part of the carrier image after QFFT are symmetrical. Then, the DCT is applied to the colored watermark, and after multiplying a factor, the RGB components of the watermark are embedded into the corresponding part of the carrier image lossless and spread into the whole image, hence enhancing the intangibility. The experimental result shows that the presented algorithm improves peak signal-to-noise ratio (PSNR) by 10 dB compared with color watermarking algorithm based on traditional QFFT.