Multiple Watermarking Algorithm Based on Spread Transform Dither Modulation.

Multiple watermarking technique, embedding several watermarks in one carrier, has enabled many interesting applications. In this study, a novel multiple watermarking algorithm is proposed based on the spirit of spread transform dither modulation (STDM). It can embed multiple watermarks into the same region and the same transform domain of one image; meanwhile, the embedded watermarks can be extracted independently and blindly in the detector without any interference. Furthermore, to improve the fidelity of the watermarked image, the properties of the dither modulation quantizer and the proposed multiple watermarks embedding strategy are investigated, and two practical optimization methods are proposed. Finally, to enhance the application flexibility, an extension of the proposed algorithm is proposed which can sequentially embeds different watermarks into one image during each stage of its circulation. Compared with the pioneering multiple watermarking algorithms, the proposed one owns more flexibility in practical application and is more robust against distortion due to basic operations such as random noise, JPEG compression and volumetric scaling.