Improved spread transform dither modulation-based watermark algorithm based on step projection

Quantization Index Modulation is an important class of watermark methods, which has been widely used in blind watermark applications. And it is well known that spread transform dither modulation (STDM), as an extension of QIM, has good performance in robustness to random noise and re-quantization. However, the quantization step sizes used in STDM are random numbers not taking the feature of the image into account. In this paper, we proposed a step projection-based STDM algorithm, which applies a novel way to incorporate the modified perceptual model with STDM framework. Experimental results indicate that our proposed scheme counters the weakness of the original STDM, the excessive sensitivity to volumetric scaling, successfully. Compared with the former proposed modified schemes of STDM, our proposed scheme have considerable advantages, especially in robustness to Gauss Noise, Salt&Pepper Noise and JPEG compression.