| 摘要 |
An apparatus and method for digital watermarking using nonlinear quantization are provided. The apparatus includes: an input signal processing unit which receives an original signal into which a watermark is to be embedded, performs discrete Fourier transform (DFT) of the signal, and outputs the result in predetermined number of subband units; a psychoacoustic model unit which receives the DFT coefficients and calculates a signal to mask ratio (SMR); a watermark embedder which embeds the watermark through nonlinear quantization of the DFT coefficients, which correspond to the predetermined middle frequency band, using the quantizer step size determined by the SMR; and a synthesizing unit which combines each subband except the middle frequency band and the output signal of the quantization unit, performs inverse DFT, and outputs the result. The watermarking method based on nonlinear quantization is robust against both amplitude modification and lossy compression. Using the nonlinear quantization, the embedded watermark can be extracted properly regardless of the errors in the quantizer step size, which is caused by the amplitude modification.
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