gen_lowpassgen_lowpassGenLowpassGenLowpass (Operator)

Name

gen_lowpassgen_lowpassGenLowpassGenLowpass — 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)

Description

gen_lowpassgen_lowpassGenLowpassGenLowpassGenLowpass 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_genericFftGenericFftGenericFftGeneric 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_genericFftGenericFftGenericFftGeneric is used, 'dc_edge'"dc_edge""dc_edge""dc_edge""dc_edge" can be used to gain efficiency. If fft_imagefft_imageFftImageFftImageFftImage and fft_image_invfft_image_invFftImageInvFftImageInvFftImageInv 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_genericRftGenericRftGenericRftGeneric 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

Parameters

ImageLowpassImageLowpassImageLowpassImageLowpassimageLowpass (output_object)  image objectHImageHImageHobject * (real)

Lowpass filter in the frequency domain.

FrequencyFrequencyFrequencyFrequencyfrequency (input_control)  real HTupleHTupleHtuple (real) (double) (double) (double)

Cutoff frequency.

Default value: 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 HTupleHTupleHtuple (string) (string) (HString) (char*)

Normalizing factor of the filter.

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

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

ModeModeModeModemode (input_control)  string HTupleHTupleHtuple (string) (string) (HString) (char*)

Location of the DC term in the frequency domain.

Default value: '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 HTupleHTupleHtuple (integer) (int / long) (Hlong) (Hlong)

Width of the image (filter).

Default value: 512

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

HeightHeightHeightHeightheight (input_control)  integer HTupleHTupleHtuple (integer) (int / long) (Hlong) (Hlong)

Height of the image (filter).

Default value: 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_lowpassGenLowpassGenLowpassGenLowpass returns 2 (H_MSG_TRUE) if all parameters are correct. If necessary, an exception is raised.

Possible Successors

convol_fftconvol_fftConvolFftConvolFftConvolFft

See also

gen_highpassgen_highpassGenHighpassGenHighpassGenHighpass, gen_bandpassgen_bandpassGenBandpassGenBandpassGenBandpass, gen_bandfiltergen_bandfilterGenBandfilterGenBandfilterGenBandfilter, gen_gauss_filtergen_gauss_filterGenGaussFilterGenGaussFilterGenGaussFilter, gen_mean_filtergen_mean_filterGenMeanFilterGenMeanFilterGenMeanFilter, gen_derivative_filtergen_derivative_filterGenDerivativeFilterGenDerivativeFilterGenDerivativeFilter

Module

Foundation