Performance Factors Analysis of a Wavelet-based Watermarking Method

The essential performance metrics of a robust watermark include robustness, imperceptibility, watermark capacity and security. In addition, computational cost is important for practicality. Wavelet-based image watermarking methods exploit the frequency information and spatial information of the transformed data in multiple resolutions to gain robustness. Although the Human Visual System (HVS) model offers imperceptibility in wavelet-based watermarking, it suffers high computational cost. In this paper, we examine embedding strength determined by a HVS model, a constant, and a simplified technique. The proposed simplified embedding technique significantly reduces embedding time while preserving the performance of imperceptibility and robustness. The fast embedding technique exploits implicit features of discrete wavelet transform (DWT) sub-bands, i.e. the luminosity information in the low pass band, and the edge information in the high pass bands. It achieves embedding speed comparable to a constant energy embedding process. Robustness is demonstrated with a few conventional attacks, e.g. JPEG compression, Gaussian noise insertion, image cropping, contrast adjustment, median filtering, and global geometrical distortion. Experimental visual quality is measured in Weighted-Peak Signal to Noise Ratio (W-PSNR) for high accuracy. Robustness and imperceptibility of HVS-based embedding could be trade-off with computational simplicity of a fast embedding technique.