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PIVMat 3.02

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PIVMat 3.02

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27 Apr 2006 (Updated )

A PIV Post-processing and data analysis toolbox

bwfilterf (PIVMat Toolbox)
bwfilterf (PIVMat Toolbox)
PIVMat Function Reference<< Prev | Next >> 
bwfilterf
Butterworth filter for a vector/scalar field

Description
FF = bwfilterf(F,FSIZE,ORDER) applies a lowpass Butterworth filter 
to the vector/scalar field F  with a cutoff size FSIZE (in grid units) 
and order ORDER. Dimensions of FSIZE and ORDER must match the dimension 
of the field F. If FSIZE and/or ORDER are scalar, the same cutoff and 
order is applied to each field of F. bwfilterf first Fourier-transforms 
the field(s), applies a low/high-pass transfer function and inverse 
Fourier transforms. Typical values for FSIZE are around 1-10, and typical 
values for ORDER are in the range 2-10 (positive for a low-pass filter, 
negative for a high-pass filter). Sharp filters (ie large values of 
FSIZE) may produce oscillations. 
 
FF = bwfilterf(F,FSIZE,ORDER,OPT), where OPT is a string that may 
contain one or several substrings: 
  'low', 'high':   specifies a lowpass (by default) or highpass filter 
  'trunc':         truncates the borders of width FSIZE, which are 
                   affected by the filtering. 
 
The X and Y dimensions of the fields must be even. If one of the 
dimension is odd, the last column/row is discarded. 
 
If no output argument, the result is displayed by showf. 
 
Note 1: A highpass filter of order ORDER is equivalent to a lowpass 
filter of order -ORDER. 
 
Note 2: If there are missing data in the field, it is better to first 
interpolate the data. See interpf. 
 
Example
 
   v = loadvec('*.vc7'); 
   showf(bwfilterf(v,3,8)); 
 
See Also
filterf, interpf, addnoisef, truncf, extractf. 
 
Published output in the Help browser 
   showdemo bwfilterf 

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