Compression and rotation resistant watermark using a circular chirp structure
Christopher E. Fleming, Bijan G. Mobasseri · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2006
Digital watermarks for images can be made relatively robust to luminance and chrominance changes. More challenging problems are geometric or combined intensity/geometric attacks. In this work we use an additive watermarking model, commonly used in spread spectrum, using a new spreading function. The spreading function is a 2D circular chirp that can simultaneously resist JPEG compression and image rotation. Circular chirp is derived from a block chirp by polar mapping. The resistance to compression is achieved by the available tuning parameters of a block chirp. Tuning parameters include the chirp's initial frequency and chirp rate. These two parameters can be used to perform spectral shaping to avoid JPEG compression effects. Rotational invariance is achieved by mapping the block chirp to a ring whose inner and outer diameters are selectable. The watermark is added in spatial domain but detection is performed in polar domain where rotation translates to translation.