gen_lowpassgen_lowpassGenLowpassGenLowpassgen_lowpass（算子）
名称
gen_lowpassgen_lowpassGenLowpassGenLowpassgen_lowpass — 生成一个理想的低通滤波器。
签名
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)
描述
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.
执行信息
- 多线程类型：可重入（与非独占算子并行运行）。
- 多线程作用域：全局（可从任何线程调用）。
- 未采用并行化处理。
参数
ImageLowpassImageLowpassImageLowpassImageLowpassimageLowpassimage_lowpass (输出对象) image → objectHImageHObjectHImageHobject * (real)
Lowpass filter in the frequency domain.
FrequencyFrequencyFrequencyFrequencyfrequencyfrequency (输入控制) real → HTuplefloatHTupleHtuple (real) (double) (double) (double)
Cutoff frequency.
默认值：
0.1
建议值：
0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0
限制：
Frequency >= 0
NormNormNormNormnormnorm (输入控制) string → HTuplestrHTupleHtuple (string) (string) (HString) (char*)
Normalizing factor of the filter.
默认值：
'none'
"none"
"none"
"none"
"none"
"none"
值列表：
'n'"n""n""n""n""n", 'none'"none""none""none""none""none"
ModeModeModeModemodemode (输入控制) string → HTuplestrHTupleHtuple (string) (string) (HString) (char*)
Location of the DC term in the frequency domain.
默认值：
'dc_center'
"dc_center"
"dc_center"
"dc_center"
"dc_center"
"dc_center"
值列表：
'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 (输入控制) integer → HTupleintHTupleHtuple (integer) (int / long) (Hlong) (Hlong)
Width of the image (filter).
默认值：
512
建议值：
128, 160, 192, 256, 320, 384, 512, 640, 768, 1024, 2048, 4096, 8192
HeightHeightHeightHeightheightheight (输入控制) integer → HTupleintHTupleHtuple (integer) (int / long) (Hlong) (Hlong)
Height of the image (filter).
默认值：
512
建议值：
120, 128, 144, 240, 256, 288, 480, 512, 576, 1024, 2048, 4096, 8192
示例（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')
结果
gen_lowpassgen_lowpassGenLowpassGenLowpassGenLowpassgen_lowpass 在所有参数正确时返回 2 ( H_MSG_TRUE )。如有必要，则抛出异常。
可能的后继
convol_fftconvol_fftConvolFftConvolFftConvolFftconvol_fft
另见
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
模块
基础