Parent Topic: <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/M_FFROST|ALGORITHM">ALGORITHM</a><hr>
<H4>FROST FILTER</H4>
The Frost filter is an adaptive filtering algorithm. It uses an
exponentially damped convolution kernel
which adapts itself to features based on local statistics.
The Frost filter differs from the Lee and Kuan filters with 
respect that the scene reflectivity is estimated by convolving
the observed image with the impulse response of the SAR system.
The impulse response of the SAR system is obtained by minimizing
the mean square error between the observed image and the scene
reflectivity model which is assumed to be an autoregressive process.<p>
The implementation of this filter consists of defining a
circularly symmetric filter with a set of weighting values M 
for each pixel:
<P>
<PRE>
       M = exp(- A * T)
</PRE>
where:
<P>
<PRE>
       A   =   DampFactor * Ci^2
       Ci  =   S / Im
       Im  =   mean value of intensity within window
       S   =   standard deviation of intensity within window
       T   =   the absolute value of the pixel distance
               from the centre pixel to its neighbours in 
               the filter window       

       DampFactor = exponential damping factor
</PRE>
The resulting grey-level value R for the smoothed pixel is:
<P>
<PRE>
         R = (P1*M1 + P2*M2 + ... +  Pn*Mn) / (M1 + M2 + ... + Mn)
</PRE>
where:
<P>
<PRE>
       P1 .. Pn   are grey levels of each pixel in filter window

       M1 .. Mn   are weights (as defined above) for each pixel
</PRE>
<hr>
Parent Topic: <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/M_FFROST|ALGORITHM">ALGORITHM</a><br>
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