gen_bandfiltergen_bandfiltergen_bandfilterGenBandfilterGenBandfilter (Operator)

Name

gen_bandfiltergen_bandfiltergen_bandfilterGenBandfilterGenBandfilter — Generate an ideal band filter.

Signature

Description

gen_bandfiltergen_bandfiltergen_bandfilterGenBandfilterGenBandfilter generates an ideal band filter in the frequency domain. The parameters MinFrequencyMinFrequencyMinFrequencyMinFrequencyminFrequency and MaxFrequencyMaxFrequencyMaxFrequencyMaxFrequencymaxFrequency determine the cutoff frequencies 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., MinFrequencyMinFrequencyMinFrequencyMinFrequencyminFrequency and MaxFrequencyMaxFrequencyMaxFrequencyMaxFrequencymaxFrequency 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_genericfft_genericFftGenericFftGeneric 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_genericfft_genericFftGenericFftGeneric is used, 'dc_edge'"dc_edge""dc_edge""dc_edge""dc_edge" can be used to gain efficiency. If fft_imagefft_imagefft_imageFftImageFftImage and fft_image_invfft_image_invfft_image_invFftImageInvFftImageInv 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_genericrft_genericRftGenericRftGeneric is used, ModeModeModeModemode = 'rft'"rft""rft""rft""rft" must be used. The resulting image contains an annulus with the value 0, and a value determined by the normalization outside of this annulus.

Parallelization

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

Parameters

Example (HDevelop)

* Filtering with maximum efficiency with fft_generic.
gen_bandpass(Bandfilter,0.2,0.4,'n','dc_edge',Width,Height)
fft_generic(Image,ImageFFT,'to_freq',-1,'none','dc_edge','complex')
convol_fft(ImageFFT,Bandfilter,ImageConvol)
fft_generic(ImageConvol,ImageResult,'from_freq',1,'none','dc_edge','byte')

Result

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

Possible Successors

convol_fftconvol_fftconvol_fftConvolFftConvolFft

Alternatives

gen_circlegen_circlegen_circleGenCircleGenCircle, paint_regionpaint_regionpaint_regionPaintRegionPaintRegion

See also

gen_highpassgen_highpassgen_highpassGenHighpassGenHighpass, gen_lowpassgen_lowpassgen_lowpassGenLowpassGenLowpass, gen_bandpassgen_bandpassgen_bandpassGenBandpassGenBandpass, gen_gauss_filtergen_gauss_filtergen_gauss_filterGenGaussFilterGenGaussFilter, gen_mean_filtergen_mean_filtergen_mean_filterGenMeanFilterGenMeanFilter, gen_derivative_filtergen_derivative_filtergen_derivative_filterGenDerivativeFilterGenDerivativeFilter

Module

Foundation