MASTER THESIS Video Watermarking - Computer Graphics Group ...

But the description is restricted to the former values in order to be less confusing;
proposed algorithms, processes and calculations do not change.
Figure 10 illustrates content ID spreading, watermark generation and
embedding which is described below.
Figure 10: Illustration of watermark generation and embedding
Once the watermark is generated and hidden information is encoded, the
embedding process can take place.
Blocks of each macroblock could be watermarked using formula (2) in case of
frequency domain watermarks (the transform coefficients of a block are altered to
encode one watermark element) or formula (4) in case of spatial domain
watermark (corresponding sub-block of watermark block elements is forward
transformed and added to the coefficients).
However, it not as simple as it seems. The essence of the problem consists in
intra prediction. If watermarked blocks are used for intra prediction of other
blocks, distortion caused by watermark embedding spreads into the other blocks.
If there is a sequence of predictively dependent blocks, the distortion propagates
and accumulates up into the last block of the sequence which probably causes
severe, obviously not unobtrusive, fidelity distortion. Therefore, the intra
prediction error compensation is implemented to undo the distortion.
In one block of a macroblock, the embedding process proceeds as follows (the
scheme is depicted in Figure 11). The residual is obtained using inverse
frequency transform on dequantized transform coefficients. Then, the predicted
samples of both the original and the watermarked pictures are computed. Thus,
both pictures are constructed during the process. The residual is added to
predicted samples of the original picture, clipped to allowed range and stored as a
block of the original picture. The prediction error as the difference between the
watermarked picture predicted samples and the original picture predicted
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