This module displays the input image on a window, and interactively reads the 
contours of polygons which are pointed by the operator using the mouse.
The polygons are created with a defaut gray level (field {\em gray})
set to 0 (black).

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{\bf Interactive commands~:}
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\begin{tabular}{ll}
Key 'Q'			& soft quit (save the polygons) \\
Key 'H'			& help \\
Key \verb+<SPACE>+	& list recorded polygons \\
Key 'R'			& redraw the window according to the recorded 
polygons\\
Mouse Left button 	& create a new point in the current coordinates (x,y)\\
Mouse Middle button 	& remove the last recorded point\\
Mouse Right button	& terminate the polygon and go ready for the next one\\
\end{tabular}
