Operator Reference

HALCON Operator Reference / Filters / FFT
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gen_lowpassgen_lowpassGenLowpassGenLowpassgen_lowpass (Operator)

gen_lowpassgen_lowpassGenLowpassGenLowpassgen_lowpass — Generate an ideal lowpass filter.

Signature

gen_lowpass( : ImageLowpass : Frequency, Norm, Mode, Width, Height : )

Herror gen_lowpass(Hobject* ImageLowpass, double Frequency, const char* Norm, const char* Mode, const Hlong Width, const Hlong Height)

Herror T_gen_lowpass(Hobject* ImageLowpass, const Htuple Frequency, const Htuple Norm, const Htuple Mode, const Htuple Width, const Htuple Height)

void GenLowpass(HObject* ImageLowpass, const HTuple& Frequency, const HTuple& Norm, const HTuple& Mode, const HTuple& Width, const HTuple& Height)

void HImage::GenLowpass(double Frequency, const HString& Norm, const HString& Mode, Hlong Width, Hlong Height)

void HImage::GenLowpass(double Frequency, const char* Norm, const char* Mode, Hlong Width, Hlong Height)

void HImage::GenLowpass(double Frequency, const wchar_t* Norm, const wchar_t* Mode, Hlong Width, Hlong Height)   ( Windows only)

static void HOperatorSet.GenLowpass(out HObject imageLowpass, HTuple frequency, HTuple norm, HTuple mode, HTuple width, HTuple height)

void HImage.GenLowpass(double frequency, string norm, string mode, int width, int height)

def gen_lowpass(frequency: float, norm: str, mode: str, width: int, height: int) -> HObject

Description

gen_lowpassgen_lowpassGenLowpassGenLowpassgen_lowpass generates an ideal lowpass filter in the frequency domain. The parameter FrequencyFrequencyFrequencyfrequencyfrequency determines the cutoff frequency of the filter as a fraction of the maximum (horizontal and vertical) frequency that can be represented in an image of size WidthWidthWidthwidthwidth x HeightHeightHeightheightheight, i.e., FrequencyFrequencyFrequencyfrequencyfrequency should lie between 0 and 1. To achieve a maximum overall efficiency of the filtering operation, the parameter NormNormNormnormnorm can be used to specify the normalization factor of the filter. If fft_genericfft_genericFftGenericFftGenericfft_generic and NormNormNormnormnorm = 'n'"n""n""n""n" is used the normalization in the FFT can be avoided. ModeModeModemodemode can be used to determine where the DC term of the filter lies or whether the filter should be used in the real-valued FFT. If fft_genericfft_genericFftGenericFftGenericfft_generic is used, 'dc_edge'"dc_edge""dc_edge""dc_edge""dc_edge" can be used to gain efficiency. If fft_imagefft_imageFftImageFftImagefft_image and fft_image_invfft_image_invFftImageInvFftImageInvfft_image_inv are used for filtering, NormNormNormnormnorm = 'none'"none""none""none""none" and ModeModeModemodemode = 'dc_center'"dc_center""dc_center""dc_center""dc_center" must be used. If rft_genericrft_genericRftGenericRftGenericrft_generic is used, ModeModeModemodemode = 'rft'"rft""rft""rft""rft" must be used. The resulting image has an inner part with the value set to the normalization factor, and an outer part with the value 0.

Execution Information

  • Multithreading type: reentrant (runs in parallel with non-exclusive operators).
  • Multithreading scope: global (may be called from any thread).
  • Processed without parallelization.

Parameters

ImageLowpassImageLowpassImageLowpassimageLowpassimage_lowpass (output_object)  image → objectHImageHObjectHObjectHobject * (real)

Lowpass filter in the frequency domain.

FrequencyFrequencyFrequencyfrequencyfrequency (input_control)  real → HTuplefloatHTupleHtuple (real) (double) (double) (double)

Cutoff frequency.

Default: 0.1

Suggested values: 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0

Restriction: Frequency >= 0

NormNormNormnormnorm (input_control)  string → HTuplestrHTupleHtuple (string) (string) (HString) (char*)

Normalizing factor of the filter.

Default: 'none' "none" "none" "none" "none"

List of values: 'n'"n""n""n""n", 'none'"none""none""none""none"

ModeModeModemodemode (input_control)  string → HTuplestrHTupleHtuple (string) (string) (HString) (char*)

Location of the DC term in the frequency domain.

Default: 'dc_center' "dc_center" "dc_center" "dc_center" "dc_center"

List of values: 'dc_center'"dc_center""dc_center""dc_center""dc_center", 'dc_edge'"dc_edge""dc_edge""dc_edge""dc_edge", 'rft'"rft""rft""rft""rft"

WidthWidthWidthwidthwidth (input_control)  integer → HTupleintHTupleHtuple (integer) (int / long) (Hlong) (Hlong)

Width of the image (filter).

Default: 512

Suggested values: 128, 160, 192, 256, 320, 384, 512, 640, 768, 1024, 2048, 4096, 8192

HeightHeightHeightheightheight (input_control)  integer → HTupleintHTupleHtuple (integer) (int / long) (Hlong) (Hlong)

Height of the image (filter).

Default: 512

Suggested values: 120, 128, 144, 240, 256, 288, 480, 512, 576, 1024, 2048, 4096, 8192

Example (HDevelop)

* Filtering with maximum efficiency with fft_generic.
gen_lowpass(Lowpass,0.2,'n','dc_edge',Width,Height)
fft_generic(Image,ImageFFT,'to_freq',-1,'none','dc_edge','complex')
convol_fft(ImageFFT,Lowpass,ImageConvol)
fft_generic(ImageConvol,ImageResult,'from_freq',1,'none','dc_edge','byte')

Result

gen_lowpassgen_lowpassGenLowpassGenLowpassgen_lowpass returns 2 ( H_MSG_TRUE) if all parameters are correct. If necessary, an exception is raised.

Possible Successors

convol_fftconvol_fftConvolFftConvolFftconvol_fft

See also

gen_highpassgen_highpassGenHighpassGenHighpassgen_highpass, gen_bandpassgen_bandpassGenBandpassGenBandpassgen_bandpass, gen_bandfiltergen_bandfilterGenBandfilterGenBandfiltergen_bandfilter, gen_gauss_filtergen_gauss_filterGenGaussFilterGenGaussFiltergen_gauss_filter, gen_mean_filtergen_mean_filterGenMeanFilterGenMeanFiltergen_mean_filter, gen_derivative_filtergen_derivative_filterGenDerivativeFilterGenDerivativeFiltergen_derivative_filter

Module

Foundation

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