Data hiding in angle quantization

In this paper, we present a non-linear method of embedding a signature in colour and monochrome images and demonstrate its recovery. The embedding process can be viewed as pseudo-random perturbations to angles between vector elements. The derived angles are dithered by the addition of a watermark, and encoded as a pseudo-noise sequence of dither angle offsets. This is followed by a re-quantisation for storage or transmission. The dither angles are recovered by scaling according to the pre-determined angle quantisation intervals. These intervals may be fixed according to some pattern, or they could be obtained adaptively from the local image. Performing a complex correlation with the known sequence enables recovery of sub-degree dither angles embedded in 8-bit data. This occurs without recourse to the original image. This embedding process is additive in the angular domain and therefore multiplicative in the signal domain. Since the magnitude of the image vector is conserved, the image energy is largely unaltered by the embedding process. Colour watermarks can be treated as sets of ordered triples (RGB), as pixel pairs in spatial or YIQ/YCbCr colour domain, or in a transform domain.

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