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Hello,
I was wondering whether there is a bug in the doc of the Wiener filter function:
http://software.intel.com/sites/products/documentation/hpc/ipp/ippi/ippi_ch9/functn_FilterWiener.html
THe doc says that the output is computed as:
Y = u + ( s^2 - n^2 )/ s^2 * ( x - u )
Where:
Y : filtered pixel output
u : average around that pixel
s^2 : stdDev around that pixel
n^2 : estimate of the noise stdDev
x : pixel value (src image)
What happens when s^2 < n^2 ? According to the equation, the output value would be inverted wrt to the input. Is there a sqr missing .. or am I completely lost ?
Thanks!
Gilbert
I was wondering whether there is a bug in the doc of the Wiener filter function:
http://software.intel.com/sites/products/documentation/hpc/ipp/ippi/ippi_ch9/functn_FilterWiener.html
THe doc says that the output is computed as:
Y = u + ( s^2 - n^2 )/ s^2 * ( x - u )
Where:
Y : filtered pixel output
u : average around that pixel
s^2 : stdDev around that pixel
n^2 : estimate of the noise stdDev
x : pixel value (src image)
What happens when s^2 < n^2 ? According to the equation, the output value would be inverted wrt to the input. Is there a sqr missing .. or am I completely lost ?
Thanks!
Gilbert
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Hello Gilbert,
I don't claim to understand the intricacies of the Wiener function, or its derivation. However; if you peruse the net you'll find this definition is consistent.
Paul
I don't claim to understand the intricacies of the Wiener function, or its derivation. However; if you peruse the net you'll find this definition is consistent.
Paul
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Hi Paul,
You are right, I also found the same definition on other sites. I still think that this is bad (possibility of signal inversion -- why would a filter do that?) but it has nothing with the IPP implementation. I probably need to improve my understanding on the basics of the Wiener filter.
Thanks
Gilbert
You are right, I also found the same definition on other sites. I still think that this is bad (possibility of signal inversion -- why would a filter do that?) but it has nothing with the IPP implementation. I probably need to improve my understanding on the basics of the Wiener filter.
Thanks
Gilbert
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