Elektronika 2009-11.pdf - Instytut Systemów Elektronicznych

With Internet access, it is now possible to offer scientists
and students virtual laboratories from a distance, via the World
Wide Web. Experiment-oriented problems can be offered
without the overhead incurred when maintaining a full laboratory
or a set of independent applications, often incompatible
with each other. According to the rather general definition presented
in the literature [14], virtual laboratory is a heterogeneous,
distributed environment making possible to conduct
experiments in a similar way to the physical laboratory. The
main objective of the virtual laboratory is to introduce scientists
and students to experimentation, problem solving, data
gathering, and scientific interpretation. Experiments performed
in the laboratory may be fully interactive, making possible
to change all parameters, giving access to any
intermediate results and producing detailed reports.
Virtual laboratories can also benefit from some collaboration
techniques as tele-immersion [26]. Because of the specific
character of the tasks realized in the field of computer
science, virtual laboratories are often focused on the information
processing problems rather than access to physical
tools. The most appreciated feature of such laboratory is its
modular architecture, which allows to increase the system capabilities
(e.g. by adding new functions and modules) without
the necessity to recompile the whole application. A user of
such laboratory should have the minimal knowledge of the API
(Application Programming Interface) provided by virtual laboratory
framework to create new plugins or modules. He does
not have to create all additional input-output procedures and
visual layer, hence he can focus on the actual problem.
Architecture and communication
Proposed Open Virtual Steganographic Laboratory VSL (Application
has been released under the open-source GPL licence
at http://vsl.sourceforge.net/_). for digital images is a set
of applications which form a distributed system aimed at computations.
This idea is motivated by a observation that each
procedure involved in the steganography/steganalysis can by
represented by a determinable process realizing specific action,
e.g. message embedding, message extraction, steganographic
attack, image distortion, data transfer, etc. The main
application of VSL which provides communication between
components and a user interface gives an ability to build a processing
flow that incorporates all needed modules and to simulate
an experiment. High-level package diagram (conforming
to Universal Modeling Language) representing system’s architecture
is presented in Fig. 2. The system package contains
main sub-package which is a core of logic. Main sub-package
communicates with other major packages: steganography, steganalysis,
distortions and tools. The first three elements can
consist of zero or more proper subsystems i.e. steganography
package contains external steganographic subsystems (standalone
modules which can be used independently regardless
of whole system), steganalysis package includes separate steganalysis
subsystems and distortions package - distortions
subsystems respectively. The last major package (tools) contains
various additional laboratory instruments needed to perform
entire experiment. Since cover images can be stored in
various file formats, input package responsible for reading and
preparing image to processing is needed. Display tool allows
to show processed images in a specific, important for the user
moment of experiment flow - before, after or between arranged
operations. In fact, it is just a simple image viewer integrated
into VSL. A user can examine images processed in any given
places of flow and easily compare them, for instance an image
before and after embedding. Output functionality makes it possible
to write results to a file.
The last proposed tool is Report. It provides image features
such as spatial resolution, color depth, name, etc., message
features (size of message, maximum length of message)
and image quality measures. Today, one of the most popular
distortion measures, due to the simplicity of the metric, is Peak
Fig. 2. High-level UML diagram of Virtual Steganographic Laboratory
Rys. 2. Diagram UML wysokiego poziomu wirtualnego laboratorium steganograficznego
62 ELEKTRONIKA 11/2009