gen_lowpassgen_lowpassGenLowpassGenLowpassgen_lowpass (Operator)
Name
gen_lowpassgen_lowpassGenLowpassGenLowpassgen_lowpass — Generate an ideal lowpass filter.
Signature
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)
Description
gen_lowpassgen_lowpassGenLowpassGenLowpassGenLowpassgen_lowpass generates an ideal lowpass filter in the
frequency domain. The parameter FrequencyFrequencyFrequencyFrequencyfrequencyfrequency 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 WidthWidthWidthWidthwidthwidth x HeightHeightHeightHeightheightheight, i.e.,
FrequencyFrequencyFrequencyFrequencyfrequencyfrequency should lie between 0 and 1. To achieve a maximum
overall efficiency of the filtering operation, the parameter
NormNormNormNormnormnorm can be used to specify the normalization factor of the
filter. If fft_genericfft_genericFftGenericFftGenericFftGenericfft_generic and NormNormNormNormnormnorm = 'n'"n""n""n""n""n"
is used the normalization in the FFT can be avoided. ModeModeModeModemodemode
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_genericFftGenericFftGenericFftGenericfft_generic is used, 'dc_edge'"dc_edge""dc_edge""dc_edge""dc_edge""dc_edge" can be used to gain
efficiency. If fft_imagefft_imageFftImageFftImageFftImagefft_image and fft_image_invfft_image_invFftImageInvFftImageInvFftImageInvfft_image_inv are used
for filtering, NormNormNormNormnormnorm = 'none'"none""none""none""none""none" and ModeModeModeModemodemode
= 'dc_center'"dc_center""dc_center""dc_center""dc_center""dc_center" must be used. If rft_genericrft_genericRftGenericRftGenericRftGenericrft_generic is
used, ModeModeModeModemodemode = 'rft'"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
ImageLowpassImageLowpassImageLowpassImageLowpassimageLowpassimage_lowpass (output_object) image → objectHImageHObjectHImageHobject * (real)
Lowpass filter in the frequency domain.
FrequencyFrequencyFrequencyFrequencyfrequencyfrequency (input_control) real → HTuplefloatHTupleHtuple (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
NormNormNormNormnormnorm (input_control) string → HTuplestrHTupleHtuple (string) (string) (HString) (char*)
Normalizing factor of the filter.
Default value:
'none'
"none"
"none"
"none"
"none"
"none"
List of values: 'n'"n""n""n""n""n", 'none'"none""none""none""none""none"
ModeModeModeModemodemode (input_control) string → HTuplestrHTupleHtuple (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"
"dc_center"
List of values: 'dc_center'"dc_center""dc_center""dc_center""dc_center""dc_center", 'dc_edge'"dc_edge""dc_edge""dc_edge""dc_edge""dc_edge", 'rft'"rft""rft""rft""rft""rft"
WidthWidthWidthWidthwidthwidth (input_control) integer → HTupleintHTupleHtuple (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
HeightHeightHeightHeightheightheight (input_control) integer → HTupleintHTupleHtuple (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_lowpassGenLowpassGenLowpassGenLowpassgen_lowpass returns 2 (H_MSG_TRUE) if all parameters are correct.
If necessary, an exception is raised.
Possible Successors
convol_fftconvol_fftConvolFftConvolFftConvolFftconvol_fft
See also
gen_highpassgen_highpassGenHighpassGenHighpassGenHighpassgen_highpass,
gen_bandpassgen_bandpassGenBandpassGenBandpassGenBandpassgen_bandpass,
gen_bandfiltergen_bandfilterGenBandfilterGenBandfilterGenBandfiltergen_bandfilter,
gen_gauss_filtergen_gauss_filterGenGaussFilterGenGaussFilterGenGaussFiltergen_gauss_filter,
gen_mean_filtergen_mean_filterGenMeanFilterGenMeanFilterGenMeanFiltergen_mean_filter,
gen_derivative_filtergen_derivative_filterGenDerivativeFilterGenDerivativeFilterGenDerivativeFiltergen_derivative_filter
Module
Foundation