imgaborfilt

Apply Gabor filter or filter bank to 2-D image

Syntax

[mag,phase] = imgaborfilt(A,wavelength,orientation)

[mag,phase] = imgaborfilt(A,wavelength,orientation,Name=Value)

[mag,phase] = imgaborfilt(A,gaborbank)

Description

[mag,phase] = imgaborfilt(A,wavelength,orientation) computes the magnitude and phase response of a Gabor filter for the input grayscale image A. wavelength describes the wavelength in pixels/cycle of the sinusoidal carrier. orientation is the orientation of the filter in degrees.

[mag,phase] = imgaborfilt(A,wavelength,orientation,Name=Value) applies a single Gabor filter using name-value arguments to control various aspects of filtering.

[mag,phase] = imgaborfilt(A,gaborbank) applies the Gabor filter bank, gaborbank, to the input image A.

Examples

Apply Single Gabor Filter to Input Image

Read an image into the workspace and convert the image to grayscale.

I = imread('board.tif');
I = im2gray(I);

Apply a Gabor filter to the image.

wavelength = 4;
orientation = 90;
[mag,phase] = imgaborfilt(I,wavelength,orientation);

Display the original image with plots of the magnitude and phase response calculated by the Gabor filter.

tiledlayout(1,3)
nexttile
imshow(I)
title('Original Image')
nexttile
imshow(mag,[])
title('Gabor Magnitude')
nexttile
imshow(phase,[])
title('Gabor Phase')

Apply Array of Gabor Filters to Input Image

Read image into the workspace.

I = imread('cameraman.tif');

Create array of Gabor filters, called a filter bank. This filter bank contains two orientations and two wavelengths.

gaborArray = gabor([4 8],[0 90]);

Apply filters to input image.

gaborMag = imgaborfilt(I,gaborArray);

Display results. The figure shows the magnitude response for each filter.

figure
subplot(2,2,1);
for p = 1:4
    subplot(2,2,p)
    imshow(gaborMag(:,:,p),[]);
    theta = gaborArray(p).Orientation;
    lambda = gaborArray(p).Wavelength;
    title(sprintf('Orientation=%d, Wavelength=%d',theta,lambda));
end

Input Arguments

A — 2-D grayscale image

numeric matrix

2-D grayscale image, specified as a numeric matrix.

wavelength — Wavelength of sinusoidal carrier

number

Wavelength of the sinusoidal carrier, specified as a number greater than or equal to 2, in pixels/cycle. Typical values of wavelength range from 2 up to the hypotenuse length of the input image [1].

orientation — Orientation of filter

number

Orientation of the filter in degrees, specified as a numeric scalar in the range [0, 360]. The orientation is defined as the normal direction to the sinusoidal plane wave.

gaborbank — Gabor filter bank

gabor object | array of gabor object

Gabor filter bank, specified as a gabor object or an array of gabor objects.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: [mag,phase] = imgaborfilt(A,wavelength,orientation,SpatialFrequencyBandwidth=2) specifies a spatial frequency bandwidth of two octaves.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: [mag,phase] = imgaborfilt(A,wavelength,orientation,"SpatialFrequencyBandwidth",2);

SpatialFrequencyBandwidth — Spatial-frequency bandwidth

1 (default) | numeric scalar

Spatial-frequency bandwidth, specified as a numeric scalar in units of octaves. The spatial-frequency bandwidth determines the cutoff of the filter response as frequency content in the input image varies from the preferred frequency, 1/lambda. Typical values for spatial-frequency bandwidth are in the range [0.5, 2.5].

SpatialAspectRatio — Ratio of semimajor and semiminor axes of Gaussian envelope

0.5 (default) | positive number

Ratio of the semimajor and semiminor axes of Gaussian envelope (semiminor/semimajor), specified as a positive number. This argument controls the ellipticity of the Gaussian envelope. Typical values for spatial aspect ratio are in the range [0.23, 0.92].

Output Arguments

mag — Magnitude response

numeric matrix | numeric array

Magnitude response for the Gabor filter or filter bank, returned as a numeric matrix for a single filter or a numeric array for a filter bank. The p-th plane of mag is the magnitude response for the Gabor filter of the same index, gaborbank(p).

Data Types: double

phase — Phase response

numeric matrix | numeric array

Phase response for the Gabor filter or filter bank, returned as a numeric matrix for a single filter or a numeric array for a filter bank. The p-th plane of phase is the phase response for the Gabor filter of the same index, gaborbank(p).

Data Types: double

Tips

• If the image contains Infs or NaNs, then the behavior of imgaborfilt is undefined because Gabor filtering is performed in the frequency domain.

• For all input data types other than single, imgaborfilt performs the computation in double. Input images of type single are filtered in type single. Performance optimizations may result from casting the input image to single prior to calling imgaborfilt.

References

[1] Jain, Anil K., and Farshid Farrokhnia. "Unsupervised Texture Segmentation Using Gabor Filters." Pattern Recognition 24, no. 12 (January 1991): 1167–86. https://doi.org/10.1016/0031-3203(91)90143-S.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• imgaborfilt supports the generation of C and C++ code (requires MATLAB^® Coder™). For more information, see Code Generation for Image Processing.

• The wavelength, orientation, SpatialFrequencyBandwidth, and SpatialAspectRatio must be compile-time constants.

• The filter bank syntax is not supported.

Version History

Introduced in R2015b