gen_gaborgen_gaborGenGaborGenGabor (Operator)

Name

gen_gaborgen_gaborGenGaborGenGabor — Generate a Gabor filter.

Signature

gen_gabor( : ImageFilter : Angle, Frequency, Bandwidth, Orientation, Norm, Mode, Width, Height : )

Description

gen_gaborgen_gaborGenGaborGenGaborGenGabor generates a Gabor filter with a user-definable bandpass frequency range and sign for the Hilbert transform. This is done by calculating a symmetrical filter in the frequency domain, which can be adapted by the parameters AngleAngleAngleAngleangle, FrequencyFrequencyFrequencyFrequencyfrequency, BandwidthBandwidthBandwidthBandwidthbandwidth and OrientationOrientationOrientationOrientationorientation such that a certain frequency band and a certain direction range in the spatial domain is filtered out in the frequency domain.

The parameters FrequencyFrequencyFrequencyFrequencyfrequency (central frequency = distance from the DC term) and OrientationOrientationOrientationOrientationorientation (direction) determine the center of the filter. Larger values of FrequencyFrequencyFrequencyFrequencyfrequency result in higher frequencies being passed. A value of 0 for OrientationOrientationOrientationOrientationorientation generates a horizontally oriented “crescent” (the bulge of the crescent points upward). Higher values of OrientationOrientationOrientationOrientationorientation result in the counterclockwise rotation of the crescent.

The parameters AngleAngleAngleAngleangle and BandwidthBandwidthBandwidthBandwidthbandwidth are used to determine the range of frequencies and angles being passed by the filter. The larger AngleAngleAngleAngleangle is, the smaller the range of angles passed by the filter gets (because the “crescent” gets narrower). The larger BandwidthBandwidthBandwidthBandwidthbandwidth is, the smaller the frequency band being passed gets (because the “crescent” gets thinner).

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. 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. Note that gen_gaborgen_gaborGenGaborGenGaborGenGabor cannot create a filter that can be used with rft_genericrft_genericRftGenericRftGenericRftGeneric.

The resulting image is a two-channel real-image, containing the Gabor filter in the first channel and the corresponding Hilbert filter in the second channel.

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

ImageFilterImageFilterImageFilterImageFilterimageFilter (output_object) multichannel-image → object (real)

Gabor and Hilbert filter.

AngleAngleAngleAngleangle (input_control) real → (real)

Angle range, inversely proportional to the range of orientations.

Default value: 1.4

Suggested values: 1.0, 1.2, 1.4, 1.6, 2.0, 2.5, 3.0, 5.0, 6.0, 10.0, 20.0, 30.0, 50.0, 70.0, 100.0

Typical range of values: 1.0 ≤ Angle Angle Angle Angle angle ≤ 500.0

Minimum increment: 0.001

Recommended increment: 0.1

FrequencyFrequencyFrequencyFrequencyfrequency (input_control) real → (real)

Distance of the center of the filter to the DC term.

Default value: 0.4

Suggested values: 0.0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.60, 0.65, 0.699

Typical range of values: 0.0 ≤ Frequency Frequency Frequency Frequency frequency ≤ 0.7

Minimum increment: 0.00001

Recommended increment: 0.005

BandwidthBandwidthBandwidthBandwidthbandwidth (input_control) real → (real)

Bandwidth range, inversely proportional to the range of frequencies being passed.

Default value: 1.0

Suggested values: 0.1, 0.3, 0.7, 1.0, 1.5, 2.0, 3.0, 5.0, 7.0, 10.0, 15.0, 20.0, 30.0, 50.0

Typical range of values: 0.05 ≤ Bandwidth Bandwidth Bandwidth Bandwidth bandwidth ≤ 100.0

Minimum increment: 0.001

Recommended increment: 0.1

OrientationOrientationOrientationOrientationorientation (input_control) real → (real)

Angle of the principal orientation.

Default value: 1.5

Suggested values: 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.14

Typical range of values: 0.0 ≤ Orientation Orientation Orientation Orientation orientation ≤ 3.1416

Minimum increment: 0.0001

Recommended increment: 0.05

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"

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)

gen_gabor(Filter,1.4,0.4,1.0,1.5,'n','dc_edge',512,512)
fft_generic(Image,ImageFFT,'to_freq',-1,'none','dc_edge','complex')
convol_gabor(ImageFFT,Filter,Gabor,Hilbert)
fft_generic(Gabor,GaborInv,'from_freq',1,'none','dc_edge','byte')
fft_generic(Hilbert,HilbertInv,'from_freq',1,'none','dc_edge','byte')
energy_gabor(GaborInv,HilbertInv,Energy)