gen_bandpass ( : ImageBandpass : MinFrequency, MaxFrequency, Size : )

Generate an ideal bandpass filter.

gen_bandpass generates an ideal bandpass filter in the frequency domain. The DC term is assumed to lie in the center of the image. The parameters MinFrequency and MaxFrequency determine the cutoff frequencies of the filter (in pixels). The resulting image contains an annulus with the value 255, and the value 0 outside of this annulus.


Parameters

ImageBandpass (output_object)
image -> object : byte
Bandpass filter in the frequency domain.

MinFrequency (input_control)
real -> real
Minimum frequency.
Default value: 20
Suggested values: 10, 20, 30, 40, 50, 60, 70, 100
Range of values: 1 <= MinFrequency <= 200
Minimum increment: 1
Recommended increment: 1
Restriction: MinFrequency > 0

MaxFrequency (input_control)
real -> real
Maximum frequency.
Default value: 40
Suggested values: 10, 20, 30, 40, 50, 60, 70, 100
Range of values: 1 <= MaxFrequency <= 200
Minimum increment: 1
Recommended increment: 1
Restriction: MaxFrequency > 0

Size (input_control)
integer -> integer
Size (dimension) of the image (filter).
Default value: 512
List of values: 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192


Example
my_lowpass(ObjType Image, ObjType *Result)
{
  ObjType  FFT, Bandpass, FFTConvol;
  fft__(Image,&FFT);
  gen_bandpass(&Bandpass,20,40,512);
  convol_fft__(FFT,Bandpass,&FFTConvol); 
  clear(Bandpass); clear(FFT);
  fft_inv__(FFTConvol,Result);
  clear(FFTConvol);
}

Result

gen_bandpass returns TRUE if all parameters are correct. If necessary, an exception is raised.


Possible Successors

convol_fft__


Alternatives

circle, paint_region__


See also

gen_highpass, gen_lowpass, gen_bandfilter



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