MASTER THESIS Video Watermarking - Computer Graphics Group ...

5.4.3 Cropping
In the cropping test, the tested video sequences are cropped to the resolution
given by the cropping factor (column in Table 6 named CF) which is the same as
scaling factor in the scaling test.
The cropped raw stream is compressed at the cropping factor fragment of
the former bit-rate as well as in the scaling test.
The compressed stream is black boxed to the former resolution using
MPlayer “expand” filter, and recompressed at the former bit-rate. The expansion
is applied because of the same synchronization reason as in the scaling test.
High resistance to this attack could be expected because the hidden
information bits are duplicated and randomly spread over whole frames. Thus,
even a small part of the frames should be enough for successful detection.
Anyway, the redundancy falls down with decreasing resolution, therefore the
detection success falls down too.
Table 6: Cropping test results
The test has finished as expected. The inconsistencies in monotonicity of the
results when changing the cropping factor may be caused by non-uniform
spreading of the content ID bits. Noise method is the least robust one.
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