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<H3><A NAME="SECTION0020921400000000000000">
COMPAR/WAVE</A>
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<DIV ALIGN="CENTER">
COMPAR/WAVE Imag_1 Imag_2 [N_Scal] [N_Sigma] [T_Cor] [T_Snr] [Disp] [Init]
</DIV>
Compares two images in the wavelet space (see section
<A HREF="node334.html#sec_comp">14.7</A>). At each scale the signal to noise ratio and the
correlation is calculated. The results are stored in tables <EM>T_Cor</EM> and <EM>Tab_Snr</EM> (the default names for the two tables are
``cmp_correl.tbl'' and ``cmp_snr.tbl''). <EM>N_Scal</EM> defines the
number of scales for the wavelet transform (default is 3). <EM>N_Sigma</EM> is a parameter which allows us to select the wavelet
coefficients which are taken into account in the comparison. Only the
wavelet coefficients <I>W</I><SUB><I>j</I></SUB> of the first image who verifies the
following relation are taken into account:
<BR><P></P>
<DIV ALIGN="CENTER">
<!-- MATH: \begin{displaymath}
W_j > \mbox{N\_Sigma}.\sigma_j
\end{displaymath} -->
<IMG
WIDTH="165" HEIGHT="41"
SRC="img885.gif"
ALT="\begin{displaymath}W_j > \mbox{N\_Sigma}.\sigma_j\end{displaymath}">
</DIV>
<BR CLEAR="ALL">
<P></P>
where <IMG
WIDTH="28" HEIGHT="39" ALIGN="MIDDLE" BORDER="0"
SRC="img886.gif"
ALT="$\sigma_j$">
is the standard deviation of the scale <I>j</I>.
The default value is 0, this means that all the wavelet coefficients are used.
If <EM>Disp</EM> equal to Y (yes), the results are plotted in two graphics
window (Y is the default value) by calling the two procedures PLOT/COR
and PLOT/SNR. If <EM>Init</EM> equal to <I>Y</I>, the tables
<EM>T_Cor</EM> and <EM>Tab_Snr</EM> are initialized, and if <EM>Init</EM> equal to N,
columns are added to the tables. That allows us to compare several images
to a reference image.
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<ADDRESS>
<I>Petra Nass</I>
<BR><I>1999-06-15</I>
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