In this paper

an adaptive color image-watermarking algorithm based on 3D-DCT(Three Dimensional-Discrete Cosine Transform) is proposed.The algorithm demonstrates that 3D-DCT outperforms 2D-DCT in terms of energy concentration.Since the 3D-DCT coefficients of a color image have larger magnitudes than that of the 2D-DCT coefficients

the 3D-DCT coefficients have larger perceptual capacity and then allow to embed stronger watermark signal.Based on 3D-DCT

we propose to change the watermark strength adaptively by taking account of the perceptual feature of human visual system.The experimental results show that the proposed algorithm can trade-off the conflict of transparency and robustness of invisible watermark well

the thus generated watermark can with-stand under the common attacks

such as JPEG compression

additive noise

image filtering

color and luminance/contrast alteration very well.