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_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