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