gen_highpassgen_highpassGenHighpassGenHighpass (Operator)

Name

gen_highpassgen_highpassGenHighpassGenHighpass — Generate an ideal highpass filter.

Signature

gen_highpass( : ImageHighpass : Frequency, Norm, Mode, Width, Height : )

gen_highpassgen_highpassGenHighpassGenHighpassGenHighpass generates an ideal highpass 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 0, and an outer part with the value determined by the normalization factor.

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

ImageHighpassImageHighpassImageHighpassImageHighpassimageHighpass (output_object) image → object (real)

Highpass filter in the frequency domain.

FrequencyFrequencyFrequencyFrequencyfrequency (input_control) real → (real)

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 → (string)

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 → (string)

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 → (integer)

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 → (integer)

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_highpass(Highpass,0.2,'n','dc_edge',Width,Height)
fft_generic(Image,ImageFFT,'to_freq',-1,'none','dc_edge','complex')
convol_fft(ImageFFT,Highpass,ImageConvol)
fft_generic(ImageConvol,ImageResult,'from_freq',1,'none','dc_edge','byte')

Result

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

Possible Successors

convol_fftconvol_fftConvolFftConvolFftConvolFft

Module

Foundation

Operators