04-12-2012, 01:06 PM
Introduction to Watermark
Introduction to Watermark.ppt (Size: 642 KB / Downloads: 268)
Motive of watermarking
Recent advancements in computer technologies offer many facilities for duplication, distribution, creation, and manipulation of digital contents.
Encryption is useful for transmission but does not provide a way to examine the original data in its protected form.
Watermarking process
Embedding stage
Spatial domain
flipping the low-order bit of each pixels
Frequency domain
embedding the watermark in mid-frequency components
relatively robust to noise, image processing and compression
the quality of the host image will be distorted significantly if too much data is embedded
Distribution stage
Compression, transmission error, and common image processing are seen as an attack on the embedded information
Watermarking properties
Perceptual transparency
Robustness
The mark should resist to
Common signal processing like lossy compression
Geometric transformation like image rotation, scaling, and cropping
Security
How easy it is to intentionally remove a watermark
Data capacity
Amount of information that can be stored within the content
Categories of digital watermark
Perceptible
Imperceptible
Robust
ownership assertion
Fragile
indicate modifications of the content
Semi-fragile
differentiate between lossy transformation that are “info. preserving” and lossy transformation which are “info. altering”
Applications
Copyright Protection
Invisible watermark which can tolerate malicious and unintentional attacks
It does not prevent people from copying the digital data
Data Hiding
It tries to invisibly embed the maximum amount of data into a host signal => this allows communication using enciphered messages without attracting the attention of a third party
Robustness is not important while invisibility and capacity are required
Conclusion
The robust watermark WRS is used to carry the copyright information while the fragile watermark C-RS-ECC is used to verify the image integrity and capable of providing the ability to recover altered image