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Abstract:
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This dissertation deals with digital watermark for grayscale images.
Digital watermark in copyright protection needs to satisfy detectability and fidelity conditions. If watermark is embedded stronger, it will be likely detectable, but it will be noticeable too, and it will jeopardize host image quality.
Here, for a well known, AWGN watermark, optimal embedding strength (minimal which guaranties watermark detectability) is determined. Optimal strength is analyzed
- for effective embedding (watermark needs to be detectable immediately after embedding)
- for watermark to be robust against expected modification (it needs to be detectable in image which will be after embedding subjected to this modification)
For effective AWGN watermark embedding, mathematical formula for optimal strength calculating is derived. For watermark robust against expected modification, one algorithm for optimal strength is given.
Among all image modifications (valumetric and geometric), lossy compression surely has an important place. Images which nowadays we can find on Net are mostly in some lossy compressed form. In such circumstances, embedded watermark will also surely be exposed to lossy compression.
This is why in this dissertation particular attention is devoted to lossy compression. Thus, its considerable part deals with AWGN watermark optimal strength, in spatial and in transform domains. Specially, here is analyzed embedding in some image subchannels in the block DCT domain, and quantization noise impact on the embedded watermark message. |