Method of quantization-watermarking

Abstract

There is provided a method of detecting a watermark included in a signal by way of quantization index modulation (QIM). The signal with the embedded watermark may have been geometrically transformed (e.g. spatially or temporally scaled) prior to detection. In order to detect the watermark even in such case, the embedder imposes an autocorrelation structure onto the embedded watermark data, for example by tiling. Initially, the detector applies conventional QIM detection. This step yields a first symbol vector, which corresponds to the embedded data when the signal was not tampered with, but does not correspond to the embedded data when the signal was subject to scaling. For example, when one data bit is embedded in each pixel of an image, 50% upsampling of the image causes a QIM detector to retrieve 3 data bits out of 3 received pixels, that is 3 data bits out of 2 original image pixels. Surprisingly, the autocorrelation of the first symbol vector will give a peak for a particular geometric transformation (e.g. the particular scaling factor). In accordance with the invention, the detector calculates said autocorrelation iunction, and uses the result to apply the inverse of the transformation, i.e. undo the scaling. A second pass of the conventional QIM detection will subsequently receive the embedded data.

Description

field of invention [0001] The invention relates to a method for quantizing watermarked audiovisual objects. Furthermore, the invention relates to a device capable of carrying out the method and also to software executable on computing hardware for carrying out the method. Furthermore, the invention relates to audiovisual objects subjected to quantized watermarking according to the method described above. Background technique [0002] Digital watermarking involves embedding auxiliary information into audiovisual objects, eg into audiovisual data objects and audio data objects. Such watermarks are crucial when claiming copyright protection of audiovisual objects, when monitoring royalties associated with the distribution of such audiovisual objects, and when potentially providing an indication of authenticity to buyers of audiovisual objects. A conventional method of watermarking an audiovisual object comprising a signal s is to add a known noise-like signal w to generate a ...

AI Technical Summary

Problems solved by technology

Therefore, a technical problem arises: QIM-style watermarking schemes are not robust enough to deliberate practical attacks

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