A
Key-based image Watermarking system using
In this thesis, we propose a novel
watermarking system that is highly robust against attacks without perceptible
image degradation. In addition, the original image is not needed in watermark
extraction. It operates either in the DWT domain or the DCT domain. This system
integrates three important ideas to provide extellent watermarking performance.
The
first idea is to use a secret key that is generated based on the watermark logo
and the host image. Based on the polarity of the transform coefficients and the
key, the original watermark can accurately be extracted.
The
second idea is to use subblock composition to filter out frequency transform
blocks that are not suitable for watermark embedding. A Tri-state Exclusive-Or (TXOR)
operator is then applied in qualified subblock to embed the watermark. This
technique further improves the robustness.
The
third idea is the deadzone shifting with human visual system. For watermark
embedded transform blocks, if the coefficients are near the threshold, they will
be shifted toward two ends so that the embedded watermark is not noticeable but
more robust.
With
the integration of the above three state-of-art techniques, the resulting
watermarking system has excellent performance. Simulation results confirm that
the proposed system is extremely robust against cropping, JPEG, JPEG2000, and
SPIHT compression.