Cryptography Reference
In-Depth Information
10.5.1 Major Problems for Watermarking Methods
The major merit of using watermarking techniques is that it is unnecessary
to have an additional space on paper for printing an additional mark such as
with QR codes. Compared to the applications using a PC-camera or scanner,
it is not easy to use watermarking techniques for the applications of print-to-
web linking technology using mobile phone camera. This is because there are
some strict restrictions in their applications. These are as follows.
Illumination Condition:
The embedded watermark must be extracted exactly from the image captured
under the lighting conditions. When using a mobile phone camera, this include
factors such as dark light indoor, or sunshine outdoor.
Photography Conditions:
Here again the embedded watermark must be extracted exactly from the
image captured by those who have used the mobile phone camera. Therefore,
the resolution of the captured image will be widely different depending on the
photography method used.
Mobile Camera Condition:
The embedded watermark must again be extracted exactly from the image
captured by the mobile phone cameras. These have different performances,
and the resolutions can be very different.
Embedding Capability:
The images must have the capability to embed watermark with enough bits in
order to index a wide range of websites. In general, the current mobile phone
camera suffers in that the maximal image pixels and the capability of image
processing are limited.
Printed Image Quality:
In order to embed more information into an image having limited image pixels
is to enhance the watermark robustness. This is done at the cost of reducing
image quality within the tolerable range of the human eye. The ability to
reduce the image quality is very limited. This is because the precondition for
using watermarking is that it should be imperceptible in the image quality.
