关键词: 分数阶Fourier变换, Chirp信号, 数字水印, 水印容量

Abstract: A novel chirp-typed watermarking scheme which uses the properties of index additivity and orthonormality of fractional Fourier transform to embed watermark in the different fractional Fourier domain is presented.With the help of the property of the impulse characteristic in the fractional Fourier domain for Chirp signal，the watermark can be detected conveniently.The general capacity of the Chirp-typed watermarking scheme also be derived.Experimental results show that the proposed watermarking algorithm is not only of good imperceptibility and security，but also is flexible and secure，and can provide protection to some common image processing.

Key words: fractional Fourier transform, Chirp signal, digital watermarking, watermarking capacity