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FILTER/WAVE I_In I_Out [Algo] [T_Filter] [Iter_Nbr] [N_Scale] [N_Sigma] [Noise]

Filters an image in the wavelet space (see section
14.6). The used algorithm for the transform depends on the
parameter *Algo* (see TRANSF/WAVE). *T_Filter* defines the
type of filtering. It can take the values 1,2,3,4 (default value is
1):
- 1.
- Thresholding (see section 14.6.4).
- 2.
- Hierarchical Thresholding (see section 14.6.5).
- 3.
- Hierarchical Wiener Filtering (see section 14.6.3).
- 4.
- Multiresolution Wiener Filtering (see section 14.6.2).

If we threshold (*T_Filter* = 1 or 2), the reconstruction can be done
iteratively, and the parameter *Iter_Nbr* specifies the number of
iterations (by default it is 1, no iteration). *N_Scale* is the
number of scales (default value is 4). *N_Sigma* is used only if we threshold. We consider
that at a given scale *j*, the significant level *L* is:

where
is the standard deviation of the noise at the scale
*j*. *Noise* is the standard deviation of the noise in the
image. If *Noise* equal to 0 (0 is the default value), the
standard deviation is estimated automatically in the program from the
histogram of the image by a 3
clipping.

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*Petra Nass*

*1999-06-15*