Watermark Bit Rate in Diverse Signal Domains

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A study of the obtainable watermark data rate for information hiding algorithms is presented in this paper. As the perceptual entropy for wideband monophonic audio signals is in the range of four to five bits per sample, a significant amount of additional information can be inserted into signal without causing any perceptual distortion. Experimental results showed that transform domain watermark embedding outperforms considerably watermark embedding in time domain and that signal decompositions with a high gain of transform coding, like the wavelet transform, are the most suitable for high data rate information hiding. Keywords—Digital watermarking, information hiding, audio watermarking, watermark data rate. I. INTRODUCTION nformation hiding techniques have developed a strong basis an area with a growing number of applications like digital rights management, covert communications, annotations, etc. In all applications given above, data hiding techniques have to satisfy two basic requirements. The first requirement is perceptual transparency, i.e. cover object (object not containing any additional data) and stego object (object containing secret message) must be perceptually indiscernible. The second constraint is high data rate of the embedded data. The simplest visualization of the requirements of information hiding in digital audio is so called magic triangle, given in Figure 1. This model is convenient for a visual representation of the required trade-offs between the capacity of the watermark data and the robustness to certain watermark attacks, while keeping the perceptual quality of the watermarked audio at an acceptable level. It is not possible to attain high robustness to signal modifications and high data rate of the embedded watermark at the same time. Therefore, if a high robustness is required from the watermarking algorithm, the bit rate of the embedded watermark will be low and vice versa, high bit rate watermarks are usually very fragile in the presence of signal modifications. However, there are some applications that do not require that the embedded watermark has a high robustness against signal modifications. In these applications, the embedded data is expected to have a high data rate and to be detected and decoded using a blind