gen_lowpass ( : ImageLowpass : Frequency, Size : )

Generate an ideal lowpass filter.

gen_lowpass generates an ideal lowpass filter in the frequency domain. The DC term is assumed to lie in the center of the image. The parameter Frequency determines the cutoff frequency of the filter (in pixels). The resulting image contains a circle of radius Frequency with the value 255, and the value 0 outside of this circle.


Parameters

ImageLowpass (output_object)
image -> object : byte
Highpass filter in the frequency domain.

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

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


Example
my_lowpass(ObjType Image, ObjType *Result, int frequency, int size)
{
  ObjType  FFT, Lowpass, FFTConvol;
  fft__(Image,&FFT);
  gen_lowpass(&Lowpass,frequency,size);
  convol_fft__(FFT,Lowpass,&FFTConvol); 
  clear(Lowpass); clear(FFT);
  fft_inv__(FFTConvol,Result);
  clear(FFTConvol);
}

Result

gen_lowpass 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_bandpass, gen_bandfilter



Copyright © 1996-1997 MVTec Software GmbH